文档 AWS SDK 示例 GitHub 存储库中还有更多 [S AWS DK 示例](https://github.com/awsdocs/aws-doc-sdk-examples)。

本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

# 使用适用于 (v3) 的 SDK JavaScript 的 DynamoDB 示例
<a name="javascript_3_dynamodb_code_examples"></a>

以下代码示例向您展示了如何使用带有 DynamoDB 的 适用于 JavaScript 的 AWS SDK (v3) 来执行操作和实现常见场景。

*基本功能*是向您展示如何在服务中执行基本操作的代码示例。

*操作*是大型程序的代码摘录，必须在上下文中运行。您可以通过操作了解如何调用单个服务函数，还可以通过函数相关场景的上下文查看操作。

*场景*是向您演示如何通过在一个服务中调用多个函数或与其他 AWS 服务结合来完成特定任务的代码示例。

每个示例都包含一个指向完整源代码的链接，您可以从中找到有关如何在上下文中设置和运行代码的说明。

**Topics**
+ [开始使用](#get_started)
+ [基本功能](#basics)
+ [操作](#actions)
+ [场景](#scenarios)
+ [无服务器示例](#serverless_examples)

## 开始使用
<a name="get_started"></a>

### 开始使用 DynamoDB
<a name="dynamodb_Hello_javascript_3_topic"></a>

以下代码示例显示如何开始使用 DynamoDB。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
有关在中使用 DynamoDB 的更多详细信息，请参阅使用[编程](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/programming-with-javascript.html) DynamoDB 适用于 JavaScript 的 AWS SDK。 JavaScript  

```
import { ListTablesCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

export const main = async () => {
  const command = new ListTablesCommand({});

  const response = await client.send(command);
  console.log(response.TableNames.join("\n"));
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[ListTables](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ListTablesCommand)*中的。

## 基本功能
<a name="basics"></a>

### 了解基本功能
<a name="dynamodb_Scenario_GettingStartedMovies_javascript_3_topic"></a>

以下代码示例展示了如何：
+ 创建可保存电影数据的表。
+ 在表中加入单一电影，获取并更新此电影。
+ 向 JSON 示例文件的表中写入电影数据。
+ 查询在给定年份发行的电影。
+ 扫描在年份范围内发行的电影。
+ 删除表中的电影后再删除表。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples) 中查找完整示例，了解如何进行设置和运行。

```
import { readFileSync } from "node:fs";
import {
  BillingMode,
  CreateTableCommand,
  DeleteTableCommand,
  DynamoDBClient,
  waitUntilTableExists,
} from "@aws-sdk/client-dynamodb";

/**
 * This module is a convenience library. It abstracts Amazon DynamoDB's data type
 * descriptors (such as S, N, B, and BOOL) by marshalling JavaScript objects into
 * AttributeValue shapes.
 */
import {
  BatchWriteCommand,
  DeleteCommand,
  DynamoDBDocumentClient,
  GetCommand,
  PutCommand,
  UpdateCommand,
  paginateQuery,
  paginateScan,
} from "@aws-sdk/lib-dynamodb";

// These modules are local to our GitHub repository. We recommend cloning
// the project from GitHub if you want to run this example.
// For more information, see https://github.com/awsdocs/aws-doc-sdk-examples.
import { getUniqueName } from "@aws-doc-sdk-examples/lib/utils/util-string.js";
import { dirnameFromMetaUrl } from "@aws-doc-sdk-examples/lib/utils/util-fs.js";
import { chunkArray } from "@aws-doc-sdk-examples/lib/utils/util-array.js";

const dirname = dirnameFromMetaUrl(import.meta.url);
const tableName = getUniqueName("Movies");
const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

const log = (msg) => console.log(`[SCENARIO] ${msg}`);

export const main = async () => {
  /**
   * Create a table.
   */

  const createTableCommand = new CreateTableCommand({
    TableName: tableName,
    // This example performs a large write to the database.
    // Set the billing mode to PAY_PER_REQUEST to
    // avoid throttling the large write.
    BillingMode: BillingMode.PAY_PER_REQUEST,
    // Define the attributes that are necessary for the key schema.
    AttributeDefinitions: [
      {
        AttributeName: "year",
        // 'N' is a data type descriptor that represents a number type.
        // For a list of all data type descriptors, see the following link.
        // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Programming.LowLevelAPI.html#Programming.LowLevelAPI.DataTypeDescriptors
        AttributeType: "N",
      },
      { AttributeName: "title", AttributeType: "S" },
    ],
    // The KeySchema defines the primary key. The primary key can be
    // a partition key, or a combination of a partition key and a sort key.
    // Key schema design is important. For more info, see
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/best-practices.html
    KeySchema: [
      // The way your data is accessed determines how you structure your keys.
      // The movies table will be queried for movies by year. It makes sense
      // to make year our partition (HASH) key.
      { AttributeName: "year", KeyType: "HASH" },
      { AttributeName: "title", KeyType: "RANGE" },
    ],
  });

  log("Creating a table.");
  const createTableResponse = await client.send(createTableCommand);
  log(`Table created: ${JSON.stringify(createTableResponse.TableDescription)}`);

  // This polls with DescribeTableCommand until the requested table is 'ACTIVE'.
  // You can't write to a table before it's active.
  log("Waiting for the table to be active.");
  await waitUntilTableExists({ client }, { TableName: tableName });
  log("Table active.");

  /**
   * Add a movie to the table.
   */

  log("Adding a single movie to the table.");
  // PutCommand is the first example usage of 'lib-dynamodb'.
  const putCommand = new PutCommand({
    TableName: tableName,
    Item: {
      // In 'client-dynamodb', the AttributeValue would be required (`year: { N: 1981 }`)
      // 'lib-dynamodb' simplifies the usage ( `year: 1981` )
      year: 1981,
      // The preceding KeySchema defines 'title' as our sort (RANGE) key, so 'title'
      // is required.
      title: "The Evil Dead",
      // Every other attribute is optional.
      info: {
        genres: ["Horror"],
      },
    },
  });
  await docClient.send(putCommand);
  log("The movie was added.");

  /**
   * Get a movie from the table.
   */

  log("Getting a single movie from the table.");
  const getCommand = new GetCommand({
    TableName: tableName,
    // Requires the complete primary key. For the movies table, the primary key
    // is only the id (partition key).
    Key: {
      year: 1981,
      title: "The Evil Dead",
    },
    // Set this to make sure that recent writes are reflected.
    // For more information, see https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.ReadConsistency.html.
    ConsistentRead: true,
  });
  const getResponse = await docClient.send(getCommand);
  log(`Got the movie: ${JSON.stringify(getResponse.Item)}`);

  /**
   * Update a movie in the table.
   */

  log("Updating a single movie in the table.");
  const updateCommand = new UpdateCommand({
    TableName: tableName,
    Key: { year: 1981, title: "The Evil Dead" },
    // This update expression appends "Comedy" to the list of genres.
    // For more information on update expressions, see
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html
    UpdateExpression: "set #i.#g = list_append(#i.#g, :vals)",
    ExpressionAttributeNames: { "#i": "info", "#g": "genres" },
    ExpressionAttributeValues: {
      ":vals": ["Comedy"],
    },
    ReturnValues: "ALL_NEW",
  });
  const updateResponse = await docClient.send(updateCommand);
  log(`Movie updated: ${JSON.stringify(updateResponse.Attributes)}`);

  /**
   * Delete a movie from the table.
   */

  log("Deleting a single movie from the table.");
  const deleteCommand = new DeleteCommand({
    TableName: tableName,
    Key: { year: 1981, title: "The Evil Dead" },
  });
  await docClient.send(deleteCommand);
  log("Movie deleted.");

  /**
   * Upload a batch of movies.
   */

  log("Adding movies from local JSON file.");
  const file = readFileSync(
    `${dirname}../../../../resources/sample_files/movies.json`,
  );
  const movies = JSON.parse(file.toString());
  // chunkArray is a local convenience function. It takes an array and returns
  // a generator function. The generator function yields every N items.
  const movieChunks = chunkArray(movies, 25);
  // For every chunk of 25 movies, make one BatchWrite request.
  for (const chunk of movieChunks) {
    const putRequests = chunk.map((movie) => ({
      PutRequest: {
        Item: movie,
      },
    }));

    const command = new BatchWriteCommand({
      RequestItems: {
        [tableName]: putRequests,
      },
    });

    await docClient.send(command);
  }
  log("Movies added.");

  /**
   * Query for movies by year.
   */

  log("Querying for all movies from 1981.");
  const paginatedQuery = paginateQuery(
    { client: docClient },
    {
      TableName: tableName,
      //For more information about query expressions, see
      // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Query.html#Query.KeyConditionExpressions
      KeyConditionExpression: "#y = :y",
      // 'year' is a reserved word in DynamoDB. Indicate that it's an attribute
      // name by using an expression attribute name.
      ExpressionAttributeNames: { "#y": "year" },
      ExpressionAttributeValues: { ":y": 1981 },
      ConsistentRead: true,
    },
  );
  /**
   * @type { Record<string, any>[] };
   */
  const movies1981 = [];
  for await (const page of paginatedQuery) {
    movies1981.push(...page.Items);
  }
  log(`Movies: ${movies1981.map((m) => m.title).join(", ")}`);

  /**
   * Scan the table for movies between 1980 and 1990.
   */

  log("Scan for movies released between 1980 and 1990");
  // A 'Scan' operation always reads every item in the table. If your design requires
  // the use of 'Scan', consider indexing your table or changing your design.
  // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-query-scan.html
  const paginatedScan = paginateScan(
    { client: docClient },
    {
      TableName: tableName,
      // Scan uses a filter expression instead of a key condition expression. Scan will
      // read the entire table and then apply the filter.
      FilterExpression: "#y between :y1 and :y2",
      ExpressionAttributeNames: { "#y": "year" },
      ExpressionAttributeValues: { ":y1": 1980, ":y2": 1990 },
      ConsistentRead: true,
    },
  );
  /**
   * @type { Record<string, any>[] };
   */
  const movies1980to1990 = [];
  for await (const page of paginatedScan) {
    movies1980to1990.push(...page.Items);
  }
  log(
    `Movies: ${movies1980to1990
      .map((m) => `${m.title} (${m.year})`)
      .join(", ")}`,
  );

  /**
   * Delete the table.
   */

  const deleteTableCommand = new DeleteTableCommand({ TableName: tableName });
  log(`Deleting table ${tableName}.`);
  await client.send(deleteTableCommand);
  log("Table deleted.");
};
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [BatchWriteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchWriteItemCommand)
  + [CreateTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/CreateTableCommand)
  + [DeleteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteItemCommand)
  + [DeleteTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteTableCommand)
  + [DescribeTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DescribeTableCommand)
  + [GetItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/GetItemCommand)
  + [PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)
  + [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)
  + [Scan](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ScanCommand)
  + [UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)

## 操作
<a name="actions"></a>

### `BatchExecuteStatement`
<a name="dynamodb_BatchExecuteStatement_javascript_3_topic"></a>

以下代码示例演示了如何使用 `BatchExecuteStatement`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
使用 PartiQL 创建一批项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  DynamoDBDocumentClient,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const breakfastFoods = ["Eggs", "Bacon", "Sausage"];
  const command = new BatchExecuteStatementCommand({
    Statements: breakfastFoods.map((food) => ({
      Statement: `INSERT INTO BreakfastFoods value {'Name':?}`,
      Parameters: [food],
    })),
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 获取一批项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  DynamoDBDocumentClient,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new BatchExecuteStatementCommand({
    Statements: [
      {
        Statement: "SELECT * FROM PepperMeasurements WHERE Unit=?",
        Parameters: ["Teaspoons"],
        ConsistentRead: true,
      },
      {
        Statement: "SELECT * FROM PepperMeasurements WHERE Unit=?",
        Parameters: ["Grams"],
        ConsistentRead: true,
      },
    ],
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 更新一批项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  DynamoDBDocumentClient,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const eggUpdates = [
    ["duck", "fried"],
    ["chicken", "omelette"],
  ];
  const command = new BatchExecuteStatementCommand({
    Statements: eggUpdates.map((change) => ({
      Statement: "UPDATE Eggs SET Style=? where Variety=?",
      Parameters: [change[1], change[0]],
    })),
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 删除一批项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  DynamoDBDocumentClient,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new BatchExecuteStatementCommand({
    Statements: [
      {
        Statement: "DELETE FROM Flavors where Name=?",
        Parameters: ["Grape"],
      },
      {
        Statement: "DELETE FROM Flavors where Name=?",
        Parameters: ["Strawberry"],
      },
    ],
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)*中的。

### `BatchGetItem`
<a name="dynamodb_BatchGetItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `BatchGetItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[BatchGet](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/BatchGetCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { BatchGetCommand, DynamoDBDocumentClient } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new BatchGetCommand({
    // Each key in this object is the name of a table. This example refers
    // to a Books table.
    RequestItems: {
      Books: {
        // Each entry in Keys is an object that specifies a primary key.
        Keys: [
          {
            Title: "How to AWS",
          },
          {
            Title: "DynamoDB for DBAs",
          },
        ],
        // Only return the "Title" and "PageCount" attributes.
        ProjectionExpression: "Title, PageCount",
      },
    },
  });

  const response = await docClient.send(command);
  console.log(response.Responses.Books);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-table-read-write-batch.html#dynamodb-example-table-read-write-batch-reading](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-table-read-write-batch.html#dynamodb-example-table-read-write-batch-reading)。
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[BatchGetItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchGetItemCommand)*中的。

### `BatchWriteItem`
<a name="dynamodb_BatchWriteItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `BatchWriteItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[BatchWrite](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/BatchWriteCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  BatchWriteCommand,
  DynamoDBDocumentClient,
} from "@aws-sdk/lib-dynamodb";
import { readFileSync } from "node:fs";

// These modules are local to our GitHub repository. We recommend cloning
// the project from GitHub if you want to run this example.
// For more information, see https://github.com/awsdocs/aws-doc-sdk-examples.
import { dirnameFromMetaUrl } from "@aws-doc-sdk-examples/lib/utils/util-fs.js";
import { chunkArray } from "@aws-doc-sdk-examples/lib/utils/util-array.js";

const dirname = dirnameFromMetaUrl(import.meta.url);

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const file = readFileSync(
    `${dirname}../../../../../resources/sample_files/movies.json`,
  );

  const movies = JSON.parse(file.toString());

  // chunkArray is a local convenience function. It takes an array and returns
  // a generator function. The generator function yields every N items.
  const movieChunks = chunkArray(movies, 25);

  // For every chunk of 25 movies, make one BatchWrite request.
  for (const chunk of movieChunks) {
    const putRequests = chunk.map((movie) => ({
      PutRequest: {
        Item: movie,
      },
    }));

    const command = new BatchWriteCommand({
      RequestItems: {
        // An existing table is required. A composite key of 'title' and 'year' is recommended
        // to account for duplicate titles.
        BatchWriteMoviesTable: putRequests,
      },
    });

    await docClient.send(command);
  }
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[BatchWriteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchWriteItemCommand)*中的。

### `CreateTable`
<a name="dynamodb_CreateTable_javascript_3_topic"></a>

以下代码示例演示了如何使用 `CreateTable`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。

```
import { CreateTableCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

export const main = async () => {
  const command = new CreateTableCommand({
    TableName: "EspressoDrinks",
    // For more information about data types,
    // see https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html#HowItWorks.DataTypes and
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Programming.LowLevelAPI.html#Programming.LowLevelAPI.DataTypeDescriptors
    AttributeDefinitions: [
      {
        AttributeName: "DrinkName",
        AttributeType: "S",
      },
    ],
    KeySchema: [
      {
        AttributeName: "DrinkName",
        KeyType: "HASH",
      },
    ],
    BillingMode: "PAY_PER_REQUEST",
  });

  const response = await client.send(command);
  console.log(response);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-creating-a-table](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-creating-a-table)。
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[CreateTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/CreateTableCommand)*中的。

### `DeleteItem`
<a name="dynamodb_DeleteItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `DeleteItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[DeleteCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/DeleteCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, DeleteCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new DeleteCommand({
    TableName: "Sodas",
    Key: {
      Flavor: "Cola",
    },
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-table-read-write.html#dynamodb-example-table-read-write-deleting-an-item](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-table-read-write.html#dynamodb-example-table-read-write-deleting-an-item)。
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[DeleteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteItemCommand)*中的。

### `DeleteTable`
<a name="dynamodb_DeleteTable_javascript_3_topic"></a>

以下代码示例演示了如何使用 `DeleteTable`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。

```
import { DeleteTableCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

export const main = async () => {
  const command = new DeleteTableCommand({
    TableName: "DecafCoffees",
  });

  const response = await client.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[DeleteTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteTableCommand)*中的。

### `DescribeTable`
<a name="dynamodb_DescribeTable_javascript_3_topic"></a>

以下代码示例演示了如何使用 `DescribeTable`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。

```
import { DescribeTableCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

export const main = async () => {
  const command = new DescribeTableCommand({
    TableName: "Pastries",
  });

  const response = await client.send(command);
  console.log(`TABLE NAME: ${response.Table.TableName}`);
  console.log(`TABLE ITEM COUNT: ${response.Table.ItemCount}`);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-describing-a-table](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-describing-a-table)。
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[DescribeTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DescribeTableCommand)*中的。

### `DescribeTimeToLive`
<a name="dynamodb_DescribeTimeToLive_javascript_3_topic"></a>

以下代码示例演示了如何使用 `DescribeTimeToLive`。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 适用于 JavaScript 的 AWS SDK描述现有 DynamoDB 表上的 TTL 配置。  

```
import { DynamoDBClient, DescribeTimeToLiveCommand } from "@aws-sdk/client-dynamodb";

export const describeTTL = async (tableName, region) => {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    try {
        const ttlDescription = await client.send(new DescribeTimeToLiveCommand({ TableName: tableName }));

        if (ttlDescription.TimeToLiveDescription.TimeToLiveStatus === 'ENABLED') {
            console.log("TTL is enabled for table %s.", tableName);
        } else {
            console.log("TTL is not enabled for table %s.", tableName);
        }

        return ttlDescription;
    } catch (e) {
        console.error(`Error describing table: ${e}`);
        throw e;
    }
}

// Example usage (commented out for testing)
// describeTTL('your-table-name', 'us-east-1');
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[DescribeTimeToLive](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DescribeTimeToLiveCommand)*中的。

### `ExecuteStatement`
<a name="dynamodb_ExecuteStatement_javascript_3_topic"></a>

以下代码示例演示了如何使用 `ExecuteStatement`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
使用 PartiQL 创建项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  ExecuteStatementCommand,
  DynamoDBDocumentClient,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new ExecuteStatementCommand({
    Statement: `INSERT INTO Flowers value {'Name':?}`,
    Parameters: ["Rose"],
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 获取项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  ExecuteStatementCommand,
  DynamoDBDocumentClient,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new ExecuteStatementCommand({
    Statement: "SELECT * FROM CloudTypes WHERE IsStorm=?",
    Parameters: [false],
    ConsistentRead: true,
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 更新项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  ExecuteStatementCommand,
  DynamoDBDocumentClient,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new ExecuteStatementCommand({
    Statement: "UPDATE EyeColors SET IsRecessive=? where Color=?",
    Parameters: [true, "blue"],
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
使用 PartiQL 删除项目。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

import {
  ExecuteStatementCommand,
  DynamoDBDocumentClient,
} from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new ExecuteStatementCommand({
    Statement: "DELETE FROM PaintColors where Name=?",
    Parameters: ["Purple"],
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)*中的。

### `GetItem`
<a name="dynamodb_GetItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `GetItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[GetCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/GetCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, GetCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new GetCommand({
    TableName: "AngryAnimals",
    Key: {
      CommonName: "Shoebill",
    },
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[GetItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/GetItemCommand)*中的。

### `ListTables`
<a name="dynamodb_ListTables_javascript_3_topic"></a>

以下代码示例演示了如何使用 `ListTables`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。

```
import { ListTablesCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

export const main = async () => {
  const command = new ListTablesCommand({});

  const response = await client.send(command);
  console.log(response);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-listing-tables](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-examples-using-tables.html#dynamodb-examples-using-tables-listing-tables)。
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[ListTables](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ListTablesCommand)*中的。

### `PutItem`
<a name="dynamodb_PutItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `PutItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[PutCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/PutCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { PutCommand, DynamoDBDocumentClient } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new PutCommand({
    TableName: "HappyAnimals",
    Item: {
      CommonName: "Shiba Inu",
    },
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)*中的。

### `Query`
<a name="dynamodb_Query_javascript_3_topic"></a>

以下代码示例演示了如何使用 `Query`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[QueryCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/QueryCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { QueryCommand, DynamoDBDocumentClient } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new QueryCommand({
    TableName: "CoffeeCrop",
    KeyConditionExpression:
      "OriginCountry = :originCountry AND RoastDate > :roastDate",
    ExpressionAttributeValues: {
      ":originCountry": "Ethiopia",
      ":roastDate": "2023-05-01",
    },
    ConsistentRead: true,
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关更多信息，请参阅《适用于 JavaScript 的 AWS SDK 开发人员指南》[https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-query-scan.html#dynamodb-example-table-query-scan-querying](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-query-scan.html#dynamodb-example-table-query-scan-querying)。
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### `Scan`
<a name="dynamodb_Scan_javascript_3_topic"></a>

以下代码示例演示了如何使用 `Scan`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[ScanCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/ScanCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, ScanCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new ScanCommand({
    ProjectionExpression: "#Name, Color, AvgLifeSpan",
    ExpressionAttributeNames: { "#Name": "Name" },
    TableName: "Birds",
  });

  const response = await docClient.send(command);
  for (const bird of response.Items) {
    console.log(`${bird.Name} - (${bird.Color}, ${bird.AvgLifeSpan})`);
  }
  return response;
};
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Scan](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ScanCommand)。

### `UpdateItem`
<a name="dynamodb_UpdateItem_javascript_3_topic"></a>

以下代码示例演示了如何使用 `UpdateItem`。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
此示例使用文档客户端来简化在 DynamoDB 中处理项目的过程。有关 API 的详细信息，请参阅[UpdateCommand](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-aws-sdk-lib-dynamodb/Class/UpdateCommand/)。  

```
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, UpdateCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

export const main = async () => {
  const command = new UpdateCommand({
    TableName: "Dogs",
    Key: {
      Breed: "Labrador",
    },
    UpdateExpression: "set Color = :color",
    ExpressionAttributeValues: {
      ":color": "black",
    },
    ReturnValues: "ALL_NEW",
  });

  const response = await docClient.send(command);
  console.log(response);
  return response;
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### `UpdateTimeToLive`
<a name="dynamodb_UpdateTimeToLive_javascript_3_topic"></a>

以下代码示例演示了如何使用 `UpdateTimeToLive`。

**适用于 JavaScript (v3) 的软件开发工具包**  
在现有 DynamoDB 表上启用 TTL。  

```
import { DynamoDBClient, UpdateTimeToLiveCommand } from "@aws-sdk/client-dynamodb";

export const enableTTL = async (tableName, ttlAttribute, region = 'us-east-1') => {

    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const params = {
        TableName: tableName,
        TimeToLiveSpecification: {
            Enabled: true,
            AttributeName: ttlAttribute
        }
    };

    try {
        const response = await client.send(new UpdateTimeToLiveCommand(params));
        if (response.$metadata.httpStatusCode === 200) {
            console.log(`TTL enabled successfully for table ${tableName}, using attribute name ${ttlAttribute}.`);
        } else {
            console.log(`Failed to enable TTL for table ${tableName}, response object: ${response}`);
        }
        return response;
    } catch (e) {
        console.error(`Error enabling TTL: ${e}`);
        throw e;
    }
};

// Example usage (commented out for testing)
// enableTTL('ExampleTable', 'exampleTtlAttribute');
```
在现有 DynamoDB 表上禁用 TTL。  

```
import { DynamoDBClient, UpdateTimeToLiveCommand } from "@aws-sdk/client-dynamodb";

export const disableTTL = async (tableName, ttlAttribute, region = 'us-east-1') => {

    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const params = {
        TableName: tableName,
        TimeToLiveSpecification: {
            Enabled: false,
            AttributeName: ttlAttribute
        }
    };

    try {
        const response = await client.send(new UpdateTimeToLiveCommand(params));
        if (response.$metadata.httpStatusCode === 200) {
            console.log(`TTL disabled successfully for table ${tableName}, using attribute name ${ttlAttribute}.`);
        } else {
            console.log(`Failed to disable TTL for table ${tableName}, response object: ${response}`);
        }
        return response;
    } catch (e) {
        console.error(`Error disabling TTL: ${e}`);
        throw e;
    }
};

// Example usage (commented out for testing)
// disableTTL('ExampleTable', 'exampleTtlAttribute');
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateTimeToLive](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateTimeToLiveCommand)*中的。

## 场景
<a name="scenarios"></a>

### 构建应用程序以将数据提交到 DynamoDB 表
<a name="cross_SubmitDataApp_javascript_3_topic"></a>

以下代码示例演示如何构建将数据提交到 Amazon DynamoDB 表并在用户更新该表时通知您的应用程序。

**适用于 JavaScript (v3) 的软件开发工具包**  
 此示例展示了如何构建一个应用程序，使用户能够向 Amazon DynamoDB 表提交数据，并使用 Amazon Simple Notification Service (Amazon SNS) 向管理员发送文本消息。  
 有关如何设置和运行的完整源代码和说明，请参阅上的完整示例[GitHub](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/submit-data-app)。  
该示例也可在 [适用于 JavaScript 的 AWS SDK v3 开发人员指南](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/cross-service-example-submitting-data.html)中找到。  

**本示例中使用的服务**
+ DynamoDB
+ Amazon SNS

### 将多个值与单个属性进行比较
<a name="dynamodb_Scenario_CompareMultipleValues_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中将多个值与单个属性进行比较。
+ 使用 IN 运算符将多个值与单个属性进行比较。
+ 将 IN 运算符与多个 OR 条件进行比较。
+ 了解使用 IN 对性能和表达式复杂性的好处。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用将多个值与单个属性进行比较 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  ScanCommand, 
  QueryCommand 
} = require("@aws-sdk/lib-dynamodb");

/**
 * Query or scan a DynamoDB table to find items where an attribute matches any value from a list.
 * 
 * This function demonstrates the use of the IN operator to compare a single attribute
 * against multiple possible values, which is more efficient than using multiple OR conditions.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} attributeName - The name of the attribute to compare against the values list
 * @param {Array} valuesList - List of values to compare the attribute against
 * @param {string} [partitionKeyName] - Optional name of the partition key attribute for query operations
 * @param {string} [partitionKeyValue] - Optional value of the partition key to query
 * @returns {Promise<Object>} - The response from DynamoDB containing the matching items
 */
async function compareMultipleValues(
  config,
  tableName,
  attributeName,
  valuesList,
  partitionKeyName,
  partitionKeyValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create the filter expression using the IN operator
  const filterExpression = `${attributeName} IN (${valuesList.map((_, index) => `:val${index}`).join(', ')})`;
  
  // Create expression attribute values for the values list
  const expressionAttributeValues = valuesList.reduce((acc, val, index) => {
    acc[`:val${index}`] = val;
    return acc;
  }, {});
  
  // If partition key is provided, perform a query operation
  if (partitionKeyName && partitionKeyValue) {
    const keyCondition = `${partitionKeyName} = :partitionKey`;
    expressionAttributeValues[':partitionKey'] = partitionKeyValue;
    
    // Initialize array to collect all items
    let allItems = [];
    let lastEvaluatedKey;
    
    // Use pagination to get all results
    do {
      const params = {
        TableName: tableName,
        KeyConditionExpression: keyCondition,
        FilterExpression: filterExpression,
        ExpressionAttributeValues: expressionAttributeValues
      };
      
      // Add ExclusiveStartKey if we have a lastEvaluatedKey from a previous query
      if (lastEvaluatedKey) {
        params.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      const response = await docClient.send(new QueryCommand(params));
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems = [...allItems, ...response.Items];
      }
      
      // Get the key for the next page of results
      lastEvaluatedKey = response.LastEvaluatedKey;
    } while (lastEvaluatedKey);
    
    // Return the complete result
    return {
      Items: allItems,
      Count: allItems.length
    };
  } else {
    // Otherwise, perform a scan operation
    // Initialize array to collect all items
    let allItems = [];
    let lastEvaluatedKey;
    
    // Use pagination to get all results
    do {
      const params = {
        TableName: tableName,
        FilterExpression: filterExpression,
        ExpressionAttributeValues: expressionAttributeValues
      };
      
      // Add ExclusiveStartKey if we have a lastEvaluatedKey from a previous scan
      if (lastEvaluatedKey) {
        params.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      const response = await docClient.send(new ScanCommand(params));
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems = [...allItems, ...response.Items];
      }
      
      // Get the key for the next page of results
      lastEvaluatedKey = response.LastEvaluatedKey;
    } while (lastEvaluatedKey);
    
    // Return the complete result
    return {
      Items: allItems,
      Count: allItems.length
    };
  }
}

/**
 * Alternative implementation using multiple OR conditions instead of the IN operator.
 * 
 * This function is provided for comparison to show why using the IN operator is preferable.
 * With many values, this approach becomes verbose and less efficient.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} attributeName - The name of the attribute to compare against the values list
 * @param {Array} valuesList - List of values to compare the attribute against
 * @param {string} [partitionKeyName] - Optional name of the partition key attribute for query operations
 * @param {string} [partitionKeyValue] - Optional value of the partition key to query
 * @returns {Promise<Object>} - The response from DynamoDB containing the matching items
 */
async function compareWithOrConditions(
  config,
  tableName,
  attributeName,
  valuesList,
  partitionKeyName,
  partitionKeyValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // If no values provided, return empty result
  if (!valuesList || valuesList.length === 0) {
    return {
      Items: [],
      Count: 0
    };
  }
  
  // Create the filter expression using multiple OR conditions
  const filterConditions = valuesList.map((_, index) => `${attributeName} = :val${index}`);
  const filterExpression = filterConditions.join(' OR ');
  
  // Create expression attribute values for the values list
  const expressionAttributeValues = valuesList.reduce((acc, val, index) => {
    acc[`:val${index}`] = val;
    return acc;
  }, {});
  
  // If partition key is provided, perform a query operation
  if (partitionKeyName && partitionKeyValue) {
    const keyCondition = `${partitionKeyName} = :partitionKey`;
    expressionAttributeValues[':partitionKey'] = partitionKeyValue;
    
    // Initialize array to collect all items
    let allItems = [];
    let lastEvaluatedKey;
    
    // Use pagination to get all results
    do {
      const params = {
        TableName: tableName,
        KeyConditionExpression: keyCondition,
        FilterExpression: filterExpression,
        ExpressionAttributeValues: expressionAttributeValues
      };
      
      // Add ExclusiveStartKey if we have a lastEvaluatedKey from a previous query
      if (lastEvaluatedKey) {
        params.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      const response = await docClient.send(new QueryCommand(params));
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems = [...allItems, ...response.Items];
      }
      
      // Get the key for the next page of results
      lastEvaluatedKey = response.LastEvaluatedKey;
    } while (lastEvaluatedKey);
    
    // Return the complete result
    return {
      Items: allItems,
      Count: allItems.length
    };
  } else {
    // Otherwise, perform a scan operation
    // Initialize array to collect all items
    let allItems = [];
    let lastEvaluatedKey;
    
    // Use pagination to get all results
    do {
      const params = {
        TableName: tableName,
        FilterExpression: filterExpression,
        ExpressionAttributeValues: expressionAttributeValues
      };
      
      // Add ExclusiveStartKey if we have a lastEvaluatedKey from a previous scan
      if (lastEvaluatedKey) {
        params.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      const response = await docClient.send(new ScanCommand(params));
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems = [...allItems, ...response.Items];
      }
      
      // Get the key for the next page of results
      lastEvaluatedKey = response.LastEvaluatedKey;
    } while (lastEvaluatedKey);
    
    // Return the complete result
    return {
      Items: allItems,
      Count: allItems.length
    };
  }
}
```
将多个值与进行比较的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to use the compareMultipleValues function.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const attributeName = "Category";
  const valuesList = ["Electronics", "Computers", "Accessories"];
  
  console.log(`Searching for products in any of these categories: ${valuesList.join(', ')}`);
  
  try {
    // Using the IN operator (recommended approach)
    console.log("\nApproach 1: Using the IN operator");
    const response = await compareMultipleValues(
      config,
      tableName,
      attributeName,
      valuesList
    );
    
    console.log(`Found ${response.Count} products in the specified categories`);
    
    // Using multiple OR conditions (alternative approach)
    console.log("\nApproach 2: Using multiple OR conditions");
    const response2 = await compareWithOrConditions(
      config,
      tableName,
      attributeName,
      valuesList
    );
    
    console.log(`Found ${response2.Count} products in the specified categories`);
    
    // Example with a query operation
    console.log("\nQuerying a specific manufacturer's products in multiple categories");
    const partitionKeyName = "Manufacturer";
    const partitionKeyValue = "Acme";
    
    const response3 = await compareMultipleValues(
      config,
      tableName,
      attributeName,
      valuesList,
      partitionKeyName,
      partitionKeyValue
    );
    
    console.log(`Found ${response3.Count} Acme products in the specified categories`);
    
    // Explain the benefits of using the IN operator
    console.log("\nBenefits of using the IN operator:");
    console.log("1. More concise expression compared to multiple OR conditions");
    console.log("2. Better readability and maintainability");
    console.log("3. Potentially better performance with large value lists");
    console.log("4. Simpler code that's less prone to errors");
    console.log("5. Easier to modify when adding or removing values");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)
  + [Scan](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ScanCommand)

### 有条件地更新项目的 TTL
<a name="dynamodb_UpdateItemConditionalTTL_javascript_3_topic"></a>

以下代码示例演示如何有条件地更新项目的 TTL。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用条件更新表中现有 DynamoDB 项目的 TTL。  

```
import { DynamoDBClient, UpdateItemCommand } from "@aws-sdk/client-dynamodb";
import { marshall, unmarshall } from "@aws-sdk/util-dynamodb";

export const updateItemConditional = async (tableName, partitionKey, sortKey, region = 'us-east-1', newAttribute = 'default-value') => {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const currentTime = Math.floor(Date.now() / 1000);

    const params = {
        TableName: tableName,
        Key: marshall({
            artist: partitionKey,
            album: sortKey
        }),
        UpdateExpression: "SET newAttribute = :newAttribute",
        ConditionExpression: "expireAt > :expiration",
        ExpressionAttributeValues: marshall({
            ':newAttribute': newAttribute,
            ':expiration': currentTime
        }),
        ReturnValues: "ALL_NEW"
    };

    try {
        const response = await client.send(new UpdateItemCommand(params));
        const responseData = unmarshall(response.Attributes);
        console.log("Item updated successfully: ", responseData);
        return responseData;
    } catch (error) {
        if (error.name === "ConditionalCheckFailedException") {
            console.log("Condition check failed: Item's 'expireAt' is expired.");
        } else {
            console.error("Error updating item: ", error);
        }
        throw error;
    }
};

// Example usage (commented out for testing)
// updateItemConditional('your-table-name', 'your-partition-key-value', 'your-sort-key-value');
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 对表达式运算符进行计数
<a name="dynamodb_Scenario_ExpressionOperatorCounting_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中对表达式运算符进行计数。
+ 了解 DynamoDB 的 300 个运算符限制。
+ 对复杂表达式中的运算符进行计数。
+ 优化表达式以保持在限制范围内。

**适用于 JavaScript (v3) 的软件开发工具包**  
演示使用 适用于 JavaScript 的 AWS SDK对表达式运算符进行计数。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  QueryCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Create a complex filter expression with a specified number of conditions.
 * 
 * This function demonstrates how to generate a complex expression with
 * a specific number of operators to test the 300 operator limit.
 * 
 * @param {number} conditionsCount - Number of conditions to include
 * @param {boolean} useAnd - Whether to use AND (true) or OR (false) between conditions
 * @returns {Object} - Object containing the filter expression and attribute values
 */
function createComplexFilterExpression(conditionsCount, useAnd = true) {
  // Initialize the expression parts and attribute values
  const conditions = [];
  const expressionAttributeValues = {};
  
  // Generate the specified number of conditions
  for (let i = 0; i < conditionsCount; i++) {
    // Alternate between different comparison operators for variety
    let condition;
    const valueKey = `:val${i}`;
    
    switch (i % 5) {
      case 0:
        condition = `attribute${i} = ${valueKey}`;
        expressionAttributeValues[valueKey] = `value${i}`;
        break;
      case 1:
        condition = `attribute${i} > ${valueKey}`;
        expressionAttributeValues[valueKey] = i;
        break;
      case 2:
        condition = `attribute${i} < ${valueKey}`;
        expressionAttributeValues[valueKey] = i * 10;
        break;
      case 3:
        condition = `contains(attribute${i}, ${valueKey})`;
        expressionAttributeValues[valueKey] = `substring${i}`;
        break;
      case 4:
        condition = `attribute_exists(attribute${i})`;
        break;
    }
    
    conditions.push(condition);
  }
  
  // Join the conditions with AND or OR
  const operator = useAnd ? " AND " : " OR ";
  const filterExpression = conditions.join(operator);
  
  // Calculate the operator count
  // Each condition has 1 operator (=, >, <, contains, attribute_exists)
  // Each AND or OR between conditions is 1 operator
  const operatorCount = conditionsCount + (conditionsCount > 0 ? conditionsCount - 1 : 0);
  
  return {
    filterExpression,
    expressionAttributeValues,
    operatorCount
  };
}

/**
 * Create a complex update expression with a specified number of operations.
 * 
 * This function demonstrates how to generate a complex update expression with
 * a specific number of operators to test the 300 operator limit.
 * 
 * @param {number} operationsCount - Number of operations to include
 * @returns {Object} - Object containing the update expression and attribute values
 */
function createComplexUpdateExpression(operationsCount) {
  // Initialize the expression parts and attribute values
  const setOperations = [];
  const expressionAttributeValues = {};
  
  // Generate the specified number of SET operations
  for (let i = 0; i < operationsCount; i++) {
    // Alternate between different types of SET operations
    let operation;
    const valueKey = `:val${i}`;
    
    switch (i % 3) {
      case 0:
        // Simple assignment (1 operator: =)
        operation = `attribute${i} = ${valueKey}`;
        expressionAttributeValues[valueKey] = `value${i}`;
        break;
      case 1:
        // Addition (2 operators: = and +)
        operation = `attribute${i} = attribute${i} + ${valueKey}`;
        expressionAttributeValues[valueKey] = i;
        break;
      case 2:
        // Conditional assignment with if_not_exists (2 operators: = and if_not_exists)
        operation = `attribute${i} = if_not_exists(attribute${i}, ${valueKey})`;
        expressionAttributeValues[valueKey] = i * 10;
        break;
    }
    
    setOperations.push(operation);
  }
  
  // Create the update expression
  const updateExpression = `SET ${setOperations.join(", ")}`;
  
  // Calculate the operator count
  // Each operation has 1-2 operators as noted above
  let operatorCount = 0;
  for (let i = 0; i < operationsCount; i++) {
    operatorCount += (i % 3 === 0) ? 1 : 2;
  }
  
  return {
    updateExpression,
    expressionAttributeValues,
    operatorCount
  };
}

/**
 * Test the operator limit by attempting an operation with a complex expression.
 * 
 * This function demonstrates what happens when an expression approaches or
 * exceeds the 300 operator limit.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {number} operatorCount - Target number of operators to include
 * @returns {Promise<Object>} - Result of the operation attempt
 */
async function testOperatorLimit(
  config,
  tableName,
  key,
  operatorCount
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create a complex update expression with the specified operator count
  const { updateExpression, expressionAttributeValues, operatorCount: actualCount } = 
    createComplexUpdateExpression(Math.ceil(operatorCount / 1.5)); // Adjust to get close to target count
  
  console.log(`Generated update expression with approximately ${actualCount} operators`);
  
  // Define the update parameters
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Attempt the update operation
    const response = await docClient.send(new UpdateCommand(params));
    return {
      success: true,
      message: `Operation succeeded with ${actualCount} operators`,
      data: response
    };
  } catch (error) {
    // Check if the error is due to exceeding the operator limit
    if (error.name === "ValidationException" && 
        error.message.includes("too many operators")) {
      return {
        success: false,
        message: `Operation failed: ${error.message}`,
        operatorCount: actualCount
      };
    }
    
    // Return other errors
    return {
      success: false,
      message: `Operation failed: ${error.message}`,
      error
    };
  }
}

/**
 * Break down a complex expression into multiple simpler operations.
 * 
 * This function demonstrates how to handle expressions that would exceed
 * the 300 operator limit by breaking them into multiple operations.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {number} totalOperations - Total number of operations to perform
 * @returns {Promise<Object>} - Result of the operations
 */
async function breakDownComplexExpression(
  config,
  tableName,
  key,
  totalOperations
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Calculate how many operations we can safely include in each batch
  // Using 150 as a conservative limit (well below 300)
  const operationsPerBatch = 100;
  const batchCount = Math.ceil(totalOperations / operationsPerBatch);
  
  console.log(`Breaking down ${totalOperations} operations into ${batchCount} batches`);
  
  const results = [];
  
  // Process each batch
  for (let batch = 0; batch < batchCount; batch++) {
    // Calculate the operations for this batch
    const batchStart = batch * operationsPerBatch;
    const batchEnd = Math.min(batchStart + operationsPerBatch, totalOperations);
    const batchSize = batchEnd - batchStart;
    
    console.log(`Processing batch ${batch + 1}/${batchCount} with ${batchSize} operations`);
    
    // Create an update expression for this batch
    const { updateExpression, expressionAttributeValues, operatorCount } = 
      createComplexUpdateExpression(batchSize);
    
    // Define the update parameters
    const params = {
      TableName: tableName,
      Key: key,
      UpdateExpression: updateExpression,
      ExpressionAttributeValues: expressionAttributeValues,
      ReturnValues: "UPDATED_NEW"
    };
    
    try {
      // Perform the update operation for this batch
      const response = await docClient.send(new UpdateCommand(params));
      
      results.push({
        batch: batch + 1,
        success: true,
        operatorCount,
        attributes: response.Attributes
      });
    } catch (error) {
      results.push({
        batch: batch + 1,
        success: false,
        operatorCount,
        error: error.message
      });
      
      // Stop processing if an error occurs
      break;
    }
  }
  
  return {
    totalBatches: batchCount,
    results
  };
}

/**
 * Count operators in a DynamoDB expression based on the rules in the documentation.
 * 
 * This function demonstrates how operators are counted according to the
 * DynamoDB documentation.
 * 
 * @param {string} expression - The DynamoDB expression to analyze
 * @returns {Object} - Breakdown of operator counts
 */
function countOperatorsInExpression(expression) {
  // Initialize counters for different operator types
  const counts = {
    comparisonOperators: 0,
    logicalOperators: 0,
    functions: 0,
    arithmeticOperators: 0,
    specialOperators: 0,
    total: 0
  };
  
  // Count comparison operators (=, <>, <, <=, >, >=)
  const comparisonRegex = /[^<>]=[^=]|<>|<=|>=|[^<]>[^=]|[^>]<[^=]/g;
  const comparisonMatches = expression.match(comparisonRegex) || [];
  counts.comparisonOperators = comparisonMatches.length;
  
  // Count logical operators (AND, OR, NOT)
  const andMatches = expression.match(/\bAND\b/g) || [];
  const orMatches = expression.match(/\bOR\b/g) || [];
  const notMatches = expression.match(/\bNOT\b/g) || [];
  counts.logicalOperators = andMatches.length + orMatches.length + notMatches.length;
  
  // Count functions (attribute_exists, attribute_not_exists, attribute_type, begins_with, contains, size)
  const functionRegex = /\b(attribute_exists|attribute_not_exists|attribute_type|begins_with|contains|size|if_not_exists)\(/g;
  const functionMatches = expression.match(functionRegex) || [];
  counts.functions = functionMatches.length;
  
  // Count arithmetic operators (+ and -)
  const arithmeticMatches = expression.match(/[a-zA-Z0-9_)\]]\s*[\+\-]\s*[a-zA-Z0-9_(:]/g) || [];
  counts.arithmeticOperators = arithmeticMatches.length;
  
  // Count special operators (BETWEEN, IN)
  const betweenMatches = expression.match(/\bBETWEEN\b/g) || [];
  const inMatches = expression.match(/\bIN\b/g) || [];
  counts.specialOperators = betweenMatches.length + inMatches.length;
  
  // Add extra operators for BETWEEN (each BETWEEN includes an AND)
  counts.logicalOperators += betweenMatches.length;
  
  // Calculate total
  counts.total = counts.comparisonOperators + 
                 counts.logicalOperators + 
                 counts.functions + 
                 counts.arithmeticOperators + 
                 counts.specialOperators;
  
  return counts;
}
```
使用表达式运算符计数的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to work with expression operator counting.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const key = { ProductId: "P12345" };
  
  console.log("Demonstrating DynamoDB expression operator counting and the 300 operator limit");
  
  try {
    // Example 1: Analyze a simple expression
    console.log("\nExample 1: Analyzing a simple expression");
    const simpleExpression = "Price = :price AND Rating > :rating AND Category IN (:cat1, :cat2, :cat3)";
    const simpleCount = countOperatorsInExpression(simpleExpression);
    
    console.log(`Expression: ${simpleExpression}`);
    console.log("Operator count breakdown:");
    console.log(`- Comparison operators: ${simpleCount.comparisonOperators}`);
    console.log(`- Logical operators: ${simpleCount.logicalOperators}`);
    console.log(`- Functions: ${simpleCount.functions}`);
    console.log(`- Arithmetic operators: ${simpleCount.arithmeticOperators}`);
    console.log(`- Special operators: ${simpleCount.specialOperators}`);
    console.log(`- Total operators: ${simpleCount.total}`);
    
    // Example 2: Analyze a complex expression
    console.log("\nExample 2: Analyzing a complex expression");
    const complexExpression = 
      "(attribute_exists(Category) AND Size BETWEEN :min AND :max) OR " +
      "(Price > :price AND contains(Description, :keyword) AND " +
      "(Rating >= :minRating OR Reviews > :minReviews))";
    const complexCount = countOperatorsInExpression(complexExpression);
    
    console.log(`Expression: ${complexExpression}`);
    console.log("Operator count breakdown:");
    console.log(`- Comparison operators: ${complexCount.comparisonOperators}`);
    console.log(`- Logical operators: ${complexCount.logicalOperators}`);
    console.log(`- Functions: ${complexCount.functions}`);
    console.log(`- Arithmetic operators: ${complexCount.arithmeticOperators}`);
    console.log(`- Special operators: ${complexCount.specialOperators}`);
    console.log(`- Total operators: ${complexCount.total}`);
    
    // Example 3: Test approaching the operator limit
    console.log("\nExample 3: Testing an expression approaching the operator limit");
    const approachingLimit = await testOperatorLimit(config, tableName, key, 290);
    console.log(approachingLimit.message);
    
    // Example 4: Test exceeding the operator limit
    console.log("\nExample 4: Testing an expression exceeding the operator limit");
    const exceedingLimit = await testOperatorLimit(config, tableName, key, 310);
    console.log(exceedingLimit.message);
    
    // Example 5: Breaking down a complex expression
    console.log("\nExample 5: Breaking down a complex expression into multiple operations");
    const breakdownResult = await breakDownComplexExpression(config, tableName, key, 500);
    console.log(`Processed ${breakdownResult.results.length} of ${breakdownResult.totalBatches} batches`);
    
    // Explain the operator counting rules
    console.log("\nKey points about DynamoDB expression operator counting:");
    console.log("1. The maximum number of operators in any expression is 300");
    console.log("2. Each comparison operator (=, <>, <, <=, >, >=) counts as 1 operator");
    console.log("3. Each logical operator (AND, OR, NOT) counts as 1 operator");
    console.log("4. Each function call (attribute_exists, contains, etc.) counts as 1 operator");
    console.log("5. Each arithmetic operator (+ or -) counts as 1 operator");
    console.log("6. BETWEEN counts as 2 operators (BETWEEN itself and the AND within it)");
    console.log("7. IN counts as 1 operator regardless of the number of values");
    console.log("8. Parentheses for grouping and attribute paths don't count as operators");
    console.log("9. When you exceed the limit, the error always reports '301 operators'");
    console.log("10. For complex operations, break them into multiple smaller operations");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 创建无服务器应用程序来管理照片
<a name="cross_PAM_javascript_3_topic"></a>

以下代码示例演示如何创建无服务器应用程序，让用户能够使用标签管理照片。

**适用于 JavaScript (v3) 的软件开发工具包**  
 演示如何开发照片资产管理应用程序，该应用程序使用 Amazon Rekognition 检测图像中的标签并将其存储以供日后检索。  
有关如何设置和运行的完整源代码和说明，请参阅上的完整示例[ GitHub](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/photo-asset-manager)。  
要深入了解这个例子的起源，请参阅 [AWS 社区](https://community.aws/posts/cloud-journeys/01-serverless-image-recognition-app)上的博文。  

**本示例中使用的服务**
+ API Gateway
+ DynamoDB
+ Lambda
+ Amazon Rekognition
+ Amazon S3
+ Amazon SNS

### 创建启用了热吞吐量的表
<a name="dynamodb_CreateTableWarmThroughput_javascript_3_topic"></a>

以下代码示例演示如何创建一个启用了热吞吐量的表。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 适用于 JavaScript 的 AWS SDK通过热吞吐量设置创建 DynamoDB 表。  

```
import { DynamoDBClient, CreateTableCommand } from "@aws-sdk/client-dynamodb";

export async function createDynamoDBTableWithWarmThroughput(
  tableName,
  partitionKey,
  sortKey,
  miscKeyAttr,
  nonKeyAttr,
  tableProvisionedReadUnits,
  tableProvisionedWriteUnits,
  tableWarmReads,
  tableWarmWrites,
  indexName,
  indexProvisionedReadUnits,
  indexProvisionedWriteUnits,
  indexWarmReads,
  indexWarmWrites,
  region = "us-east-1"
) {
  try {
    const ddbClient = new DynamoDBClient({ region: region });
    const command = new CreateTableCommand({
      TableName: tableName,
      AttributeDefinitions: [
          { AttributeName: partitionKey, AttributeType: "S" },
          { AttributeName: sortKey, AttributeType: "S" },
          { AttributeName: miscKeyAttr, AttributeType: "N" },
      ],
      KeySchema: [
          { AttributeName: partitionKey, KeyType: "HASH" },
          { AttributeName: sortKey, KeyType: "RANGE" },
      ],
      ProvisionedThroughput: {
          ReadCapacityUnits: tableProvisionedReadUnits,
          WriteCapacityUnits: tableProvisionedWriteUnits,
      },
      WarmThroughput: {
          ReadUnitsPerSecond: tableWarmReads,
          WriteUnitsPerSecond: tableWarmWrites,
      },
      GlobalSecondaryIndexes: [
          {
            IndexName: indexName,
            KeySchema: [
                { AttributeName: sortKey, KeyType: "HASH" },
                { AttributeName: miscKeyAttr, KeyType: "RANGE" },
            ],
            Projection: {
                ProjectionType: "INCLUDE",
                NonKeyAttributes: [nonKeyAttr],
            },
            ProvisionedThroughput: {
                ReadCapacityUnits: indexProvisionedReadUnits,
                WriteCapacityUnits: indexProvisionedWriteUnits,
            },
            WarmThroughput: {
                ReadUnitsPerSecond: indexWarmReads,
                WriteUnitsPerSecond: indexWarmWrites,
            },
          },
      ],
    });
    const response = await ddbClient.send(command);
    console.log(response);
    return response;
  } catch (error) {
    console.error(`Error creating table: ${error}`);
    throw error;
  }
}

// Example usage (commented out for testing)
/*
createDynamoDBTableWithWarmThroughput(
  'example-table',
  'pk',
  'sk',
  'gsiKey',
  'data',
  10, 10, 5, 5,
  'example-index',
  5, 5, 2, 2
);
*/
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[CreateTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/CreateTableCommand)*中的。

### 创建设置了 TTL 的项目
<a name="dynamodb_PutItemTTL_javascript_3_topic"></a>

以下代码示例演示如何创建具有 TTL 的项目。

**适用于 JavaScript (v3) 的软件开发工具包**  

```
import { DynamoDBClient, PutItemCommand } from "@aws-sdk/client-dynamodb";

export function createDynamoDBItem(table_name, region, partition_key, sort_key) {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    // Get the current time in epoch second format
    const current_time = Math.floor(new Date().getTime() / 1000);

    // Calculate the expireAt time (90 days from now) in epoch second format
    const expire_at = Math.floor((new Date().getTime() + 90 * 24 * 60 * 60 * 1000) / 1000);

    // Create DynamoDB item
    const item = {
        'partitionKey': {'S': partition_key},
        'sortKey': {'S': sort_key},
        'createdAt': {'N': current_time.toString()},
        'expireAt': {'N': expire_at.toString()}
    };

    const putItemCommand = new PutItemCommand({
        TableName: table_name,
        Item: item,
        ProvisionedThroughput: {
            ReadCapacityUnits: 1,
            WriteCapacityUnits: 1,
        },
    });

    client.send(putItemCommand, function(err, data) {
        if (err) {
            console.log("Exception encountered when creating item %s, here's what happened: ", data, err);
            throw err;
        } else {
            console.log("Item created successfully: %s.", data);
            return data;
        }
    });
}

// Example usage (commented out for testing)
// createDynamoDBItem('your-table-name', 'us-east-1', 'your-partition-key-value', 'your-sort-key-value');
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)*中的。

### 使用 PartiQL DELETE 删除数据
<a name="dynamodb_PartiQLDelete_javascript_3_topic"></a>

以下代码示例演示如何使用 PartiQL DELETE 语句删除数据。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 partiQL DELETE 语句从 DynamoDB 表中删除项目。 适用于 JavaScript 的 AWS SDK  

```
/**
 * This example demonstrates how to delete items from a DynamoDB table using PartiQL.
 * It shows different ways to delete documents with various index types.
 */
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  ExecuteStatementCommand,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

/**
 * Delete a single item by its partition key using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @returns The response from the ExecuteStatementCommand
 */
export const deleteItemByPartitionKey = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `DELETE FROM "${tableName}" WHERE ${partitionKeyName} = ?`,
    Parameters: [partitionKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item deleted successfully");
    return data;
  } catch (err) {
    console.error("Error deleting item:", err);
    throw err;
  }
};

/**
 * Delete an item by its composite key (partition key + sort key) using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param sortKeyName - The name of the sort key attribute
 * @param sortKeyValue - The value of the sort key
 * @returns The response from the ExecuteStatementCommand
 */
export const deleteItemByCompositeKey = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  sortKeyName: string,
  sortKeyValue: string | number
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `DELETE FROM "${tableName}" WHERE ${partitionKeyName} = ? AND ${sortKeyName} = ?`,
    Parameters: [partitionKeyValue, sortKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item deleted successfully");
    return data;
  } catch (err) {
    console.error("Error deleting item:", err);
    throw err;
  }
};

/**
 * Delete an item with a condition to ensure the delete only happens if a condition is met.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param conditionAttribute - The attribute to check in the condition
 * @param conditionValue - The value to compare against in the condition
 * @returns The response from the ExecuteStatementCommand
 */
export const deleteItemWithCondition = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  conditionAttribute: string,
  conditionValue: any
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `DELETE FROM "${tableName}" WHERE ${partitionKeyName} = ? AND ${conditionAttribute} = ?`,
    Parameters: [partitionKeyValue, conditionValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item deleted with condition successfully");
    return data;
  } catch (err) {
    console.error("Error deleting item with condition:", err);
    throw err;
  }
};

/**
 * Batch delete multiple items using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param keys - Array of objects containing key information
 * @returns The response from the BatchExecuteStatementCommand
 */
export const batchDeleteItems = async (
  tableName: string,
  keys: Array<{
    partitionKeyName: string;
    partitionKeyValue: string | number;
    sortKeyName?: string;
    sortKeyValue?: string | number;
  }>
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  // Create statements for each delete
  const statements = keys.map((key) => {
    if (key.sortKeyName && key.sortKeyValue !== undefined) {
      return {
        Statement: `DELETE FROM "${tableName}" WHERE ${key.partitionKeyName} = ? AND ${key.sortKeyName} = ?`,
        Parameters: [key.partitionKeyValue, key.sortKeyValue],
      };
    } else {
      return {
        Statement: `DELETE FROM "${tableName}" WHERE ${key.partitionKeyName} = ?`,
        Parameters: [key.partitionKeyValue],
      };
    }
  });

  const params = {
    Statements: statements,
  };

  try {
    const data = await docClient.send(new BatchExecuteStatementCommand(params));
    console.log("Items batch deleted successfully");
    return data;
  } catch (err) {
    console.error("Error batch deleting items:", err);
    throw err;
  }
};

/**
 * Delete multiple items that match a filter condition.
 * Note: This performs a scan operation which can be expensive on large tables.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param filterAttribute - The attribute to filter on
 * @param filterValue - The value to filter by
 * @returns The response from the ExecuteStatementCommand
 */
export const deleteItemsByFilter = async (
  tableName: string,
  filterAttribute: string,
  filterValue: any
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `DELETE FROM "${tableName}" WHERE ${filterAttribute} = ?`,
    Parameters: [filterValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Items deleted by filter successfully");
    return data;
  } catch (err) {
    console.error("Error deleting items by filter:", err);
    throw err;
  }
};

/**
 * Example usage showing how to delete items with different index types
 */
export const deleteExamples = async () => {
  // Delete an item by partition key (simple primary key)
  await deleteItemByPartitionKey("UsersTable", "userId", "user123");

  // Delete an item by composite key (partition key + sort key)
  await deleteItemByCompositeKey(
    "OrdersTable",
    "orderId",
    "order456",
    "productId",
    "prod789"
  );

  // Delete with a condition
  await deleteItemWithCondition(
    "UsersTable",
    "userId",
    "user789",
    "userStatus",
    "inactive"
  );

  // Batch delete multiple items
  await batchDeleteItems("UsersTable", [
    { partitionKeyName: "userId", partitionKeyValue: "user234" },
    { partitionKeyName: "userId", partitionKeyValue: "user345" },
  ]);

  // Batch delete items with composite keys
  await batchDeleteItems("OrdersTable", [
    {
      partitionKeyName: "orderId",
      partitionKeyValue: "order567",
      sortKeyName: "productId",
      sortKeyValue: "prod123",
    },
    {
      partitionKeyName: "orderId",
      partitionKeyValue: "order678",
      sortKeyName: "productId",
      sortKeyValue: "prod456",
    },
  ]);

  // Delete items by filter (use with caution)
  await deleteItemsByFilter("UsersTable", "userStatus", "deleted");
};
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)
  + [ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)

### 使用 PartiQL INSERT 插入数据
<a name="dynamodb_PartiQLInsert_javascript_3_topic"></a>

以下代码示例演示如何使用 PartiQL INSERT 语句插入数据。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 PartiQL INSERT 语句将项目插入到 DynamoDB 表中。 适用于 JavaScript 的 AWS SDK  

```
/**
 * This example demonstrates how to insert items into a DynamoDB table using PartiQL.
 * It shows different ways to insert documents with various index types.
 */
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  ExecuteStatementCommand,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

/**
 * Insert a single item into a DynamoDB table using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param item - The item to insert
 * @returns The response from the ExecuteStatementCommand
 */
export const insertItem = async (tableName: string, item: Record<string, any>) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  // Convert the item to a string representation for PartiQL
  const itemString = JSON.stringify(item).replace(/"([^"]+)":/g, '$1:');

  const params = {
    Statement: `INSERT INTO "${tableName}" VALUE ${itemString}`,
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item inserted successfully");
    return data;
  } catch (err) {
    console.error("Error inserting item:", err);
    throw err;
  }
};

/**
 * Insert multiple items into a DynamoDB table using PartiQL batch operation.
 * This is more efficient than inserting items one by one.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param items - Array of items to insert
 * @returns The response from the BatchExecuteStatementCommand
 */
export const batchInsertItems = async (tableName: string, items: Record<string, any>[]) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  // Create statements for each item
  const statements = items.map((item) => {
    const itemString = JSON.stringify(item).replace(/"([^"]+)":/g, '$1:');
    return {
      Statement: `INSERT INTO "${tableName}" VALUE ${itemString}`,
    };
  });

  const params = {
    Statements: statements,
  };

  try {
    const data = await docClient.send(new BatchExecuteStatementCommand(params));
    console.log("Items inserted successfully");
    return data;
  } catch (err) {
    console.error("Error batch inserting items:", err);
    throw err;
  }
};

/**
 * Insert an item with a condition to prevent overwriting existing items.
 * This is useful for ensuring you don't accidentally overwrite data.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param item - The item to insert
 * @param partitionKeyName - The name of the partition key attribute
 * @returns The response from the ExecuteStatementCommand
 */
export const insertItemWithCondition = async (
  tableName: string,
  item: Record<string, any>,
  partitionKeyName: string
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const itemString = JSON.stringify(item).replace(/"([^"]+)":/g, '$1:');
  const partitionKeyValue = JSON.stringify(item[partitionKeyName]);

  const params = {
    Statement: `INSERT INTO "${tableName}" VALUE ${itemString} WHERE attribute_not_exists(${partitionKeyName})`,
    Parameters: [{ S: partitionKeyValue }],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item inserted with condition successfully");
    return data;
  } catch (err) {
    console.error("Error inserting item with condition:", err);
    throw err;
  }
};

/**
 * Example usage showing how to insert items with different index types
 */
export const insertExamples = async () => {
  // Example table with a simple primary key (just partition key)
  const simpleKeyItem = {
    userId: "user123",
    name: "John Doe",
    email: "john@example.com",
  };
  await insertItem("UsersTable", simpleKeyItem);

  // Example table with composite key (partition key + sort key)
  const compositeKeyItem = {
    orderId: "order456",
    productId: "prod789",
    quantity: 2,
    price: 29.99,
  };
  await insertItem("OrdersTable", compositeKeyItem);

  // Example with Global Secondary Index (GSI)
  // The GSI might be on the email attribute
  const gsiItem = {
    userId: "user789",
    email: "jane@example.com",
    name: "Jane Smith",
    userType: "premium",  // This could be part of a GSI
  };
  await insertItem("UsersTable", gsiItem);

  // Example with Local Secondary Index (LSI)
  // LSI uses the same partition key but different sort key
  const lsiItem = {
    orderId: "order567",  // Partition key
    productId: "prod123", // Sort key for the table
    orderDate: "2023-11-15", // Potential sort key for an LSI
    quantity: 1,
    price: 19.99,
  };
  await insertItem("OrdersTable", lsiItem);

  // Batch insert example with multiple items
  const batchItems = [
    {
      userId: "user234",
      name: "Alice Johnson",
      email: "alice@example.com",
    },
    {
      userId: "user345",
      name: "Bob Williams",
      email: "bob@example.com",
    },
  ];
  await batchInsertItems("UsersTable", batchItems);
};
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)
  + [ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)

### 从浏览器调用 Lambda 函数
<a name="cross_LambdaForBrowser_javascript_3_topic"></a>

以下代码示例显示了如何从浏览器调用 AWS Lambda 函数。

**适用于 JavaScript (v3) 的软件开发工具包**  
 您可以创建一个基于浏览器的应用程序，该应用程序使用 AWS Lambda 函数更新包含用户选择的 Amazon DynamoDB 表。此应用程序使用 适用于 JavaScript 的 AWS SDK v3。  
 有关如何设置和运行的完整源代码和说明，请参阅上的完整示例[GitHub](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/lambda-for-browser)。  

**本示例中使用的服务**
+ DynamoDB
+ Lambda

### 执行高级查询操作
<a name="dynamodb_Scenario_AdvancedQueryTechniques_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中执行高级查询操作。
+ 使用各种筛选和条件技术查询表。
+ 对大型结果集实现分页。
+ 使用全局二级索引实现备选访问模式。
+ 根据应用程序要求应用一致性控制。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用强一致性读取进行查询 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with configurable read consistency
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {boolean} useConsistentRead - Whether to use strongly consistent reads
 * @returns {Promise<Object>} - The query response
 */
async function queryWithConsistentRead(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  useConsistentRead = false
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue",
      ExpressionAttributeNames: {
        "#pk": partitionKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue }
      },
      ConsistentRead: useConsistentRead
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with consistent read: ${error}`);
    throw error;
  }
}
```
使用带的全局二级索引进行查询 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table using the primary key
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} userId - The user ID to query by (partition key)
 * @returns {Promise<Object>} - The query response
 */
async function queryTable(
  config,
  tableName,
  userId
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input for the base table
    const input = {
      TableName: tableName,
      KeyConditionExpression: "user_id = :userId",
      ExpressionAttributeValues: {
        ":userId": { S: userId }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying table: ${error}`);
    throw error;
  }
}

/**
 * Queries a DynamoDB Global Secondary Index (GSI)
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} indexName - The name of the GSI to query
 * @param {string} gameId - The game ID to query by (GSI partition key)
 * @returns {Promise<Object>} - The query response
 */
async function queryGSI(
  config,
  tableName,
  indexName,
  gameId
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input for the GSI
    const input = {
      TableName: tableName,
      IndexName: indexName,
      KeyConditionExpression: "game_id = :gameId",
      ExpressionAttributeValues: {
        ":gameId": { S: gameId }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying GSI: ${error}`);
    throw error;
  }
}
```
使用 适用于 JavaScript 的 AWS SDK分页查询。  

```
/**
 * Example demonstrating how to handle large query result sets in DynamoDB using pagination
 * 
 * This example shows:
 * - How to use pagination to handle large result sets
 * - How to use LastEvaluatedKey to retrieve the next page of results
 * - How to construct subsequent query requests using ExclusiveStartKey
 */
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with pagination to handle large result sets
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {number} pageSize - Number of items per page
 * @returns {Promise<Array>} - All items from the query
 */
async function queryWithPagination(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  pageSize = 25
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);
    
    // Initialize variables for pagination
    let lastEvaluatedKey = undefined;
    const allItems = [];
    let pageCount = 0;
    
    // Loop until all pages are retrieved
    do {
      // Construct the query input
      const input = {
        TableName: tableName,
        KeyConditionExpression: "#pk = :pkValue",
        Limit: pageSize,
        ExpressionAttributeNames: {
          "#pk": partitionKeyName
        },
        ExpressionAttributeValues: {
          ":pkValue": { S: partitionKeyValue }
        }
      };
      
      // Add ExclusiveStartKey if we have a LastEvaluatedKey from a previous query
      if (lastEvaluatedKey) {
        input.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      // Execute the query
      const command = new QueryCommand(input);
      const response = await client.send(command);
      
      // Process the current page of results
      pageCount++;
      console.log(`Processing page ${pageCount} with ${response.Items.length} items`);
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems.push(...response.Items);
      }
      
      // Get the LastEvaluatedKey for the next page
      lastEvaluatedKey = response.LastEvaluatedKey;
      
    } while (lastEvaluatedKey); // Continue until there are no more pages
    
    console.log(`Query complete. Retrieved ${allItems.length} items in ${pageCount} pages.`);
    return allItems;
  } catch (error) {
    console.error(`Error querying with pagination: ${error}`);
    throw error;
  }
}

/**
 * Example usage:
 * 
 * // Query all items in the "AWS DynamoDB" forum with pagination
 * const allItems = await queryWithPagination(
 *   { region: "us-west-2" },
 *   "ForumThreads",
 *   "ForumName",
 *   "AWS DynamoDB",
 *   25 // 25 items per page
 * );
 * 
 * console.log(`Total items retrieved: ${allItems.length}`);
 * 
 * // Notes on pagination:
 * // - LastEvaluatedKey contains the primary key of the last evaluated item
 * // - When LastEvaluatedKey is undefined/null, there are no more items to retrieve
 * // - ExclusiveStartKey tells DynamoDB where to start the next page
 * // - Pagination helps manage memory usage for large result sets
 * // - Each page requires a separate network request to DynamoDB
 */

module.exports = { queryWithPagination };
```
使用复杂的过滤器进行查询 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with a complex filter expression
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {number|string} minViews - Minimum number of views for filtering
 * @param {number|string} minReplies - Minimum number of replies for filtering
 * @param {string} requiredTag - Tag that must be present in the item's tags set
 * @returns {Promise<Object>} - The query response
 */
async function queryWithComplexFilter(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  minViews,
  minReplies,
  requiredTag
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue",
      FilterExpression: "views >= :minViews AND replies >= :minReplies AND contains(tags, :tag)",
      ExpressionAttributeNames: {
        "#pk": partitionKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":minViews": { N: minViews.toString() },
        ":minReplies": { N: minReplies.toString() },
        ":tag": { S: requiredTag }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with complex filter: ${error}`);
    throw error;
  }
}
```
使用动态构造的过滤器表达式进行查询 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

async function queryWithDynamicFilter(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  sortKeyName,
  sortKeyValue,
  filterParams = {}
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Initialize filter expression components
    let filterExpressions = [];
    const expressionAttributeValues = {
      ":pkValue": { S: partitionKeyValue },
      ":skValue": { S: sortKeyValue }
    };
    const expressionAttributeNames = {
      "#pk": partitionKeyName,
      "#sk": sortKeyName
    };

    // Add status filter if provided
    if (filterParams.status) {
      filterExpressions.push("status = :status");
      expressionAttributeValues[":status"] = { S: filterParams.status };
    }

    // Add minimum views filter if provided
    if (filterParams.minViews !== undefined) {
      filterExpressions.push("views >= :minViews");
      expressionAttributeValues[":minViews"] = { N: filterParams.minViews.toString() };
    }

    // Add author filter if provided
    if (filterParams.author) {
      filterExpressions.push("author = :author");
      expressionAttributeValues[":author"] = { S: filterParams.author };
    }

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue AND #sk = :skValue"
    };

    // Add filter expression if any filters were provided
    if (filterExpressions.length > 0) {
      input.FilterExpression = filterExpressions.join(" AND ");
    }

    // Add expression attribute names and values
    input.ExpressionAttributeNames = expressionAttributeNames;
    input.ExpressionAttributeValues = expressionAttributeValues;

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with dynamic filter: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 执行列表操作
<a name="dynamodb_Scenario_ListOperations_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中执行列表操作。
+ 向列表属性添加元素。
+ 从列表属性中移除元素。
+ 按索引更新列表中的特定元素。
+ 使用列表追加和列表索引函数。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示列表操作 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand,
  PutCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Append elements to a list attribute.
 * 
 * This function demonstrates how to use the list_append function to add elements
 * to the end of a list.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {Array} values - The values to append to the list
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function appendToList(
  config,
  tableName,
  key,
  listName,
  values
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using list_append
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${listName} = list_append(if_not_exists(${listName}, :empty_list), :values)`,
    ExpressionAttributeValues: {
      ":empty_list": [],
      ":values": values
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Prepend elements to a list attribute.
 * 
 * This function demonstrates how to use the list_append function to add elements
 * to the beginning of a list.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {Array} values - The values to prepend to the list
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function prependToList(
  config,
  tableName,
  key,
  listName,
  values
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using list_append
  // Note: To prepend, we put the new values first in the list_append function
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${listName} = list_append(:values, if_not_exists(${listName}, :empty_list))`,
    ExpressionAttributeValues: {
      ":empty_list": [],
      ":values": values
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Update a specific element in a list by index.
 * 
 * This function demonstrates how to update a specific element in a list
 * using the index notation.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {number} index - The index of the element to update
 * @param {any} value - The new value for the element
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateListElement(
  config,
  tableName,
  key,
  listName,
  index,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using index notation
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${listName}[${index}] = :value`,
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Remove an element from a list by index.
 * 
 * This function demonstrates how to remove a specific element from a list
 * using the REMOVE action with index notation.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {number} index - The index of the element to remove
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function removeListElement(
  config,
  tableName,
  key,
  listName,
  index
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using REMOVE with index notation
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `REMOVE ${listName}[${index}]`,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Concatenate two lists.
 * 
 * This function demonstrates how to concatenate two lists using the list_append function.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName1 - The name of the first list attribute
 * @param {string} listName2 - The name of the second list attribute
 * @param {string} resultListName - The name of the attribute to store the concatenated list
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function concatenateLists(
  config,
  tableName,
  key,
  listName1,
  listName2,
  resultListName
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using list_append
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${resultListName} = list_append(if_not_exists(${listName1}, :empty_list), if_not_exists(${listName2}, :empty_list))`,
    ExpressionAttributeValues: {
      ":empty_list": []
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Create a nested list structure.
 * 
 * This function demonstrates how to create and work with nested lists.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {Array} nestedLists - An array of arrays to create a nested list structure
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function createNestedList(
  config,
  tableName,
  key,
  listName,
  nestedLists
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters to create a nested list
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${listName} = :nested_lists`,
    ExpressionAttributeValues: {
      ":nested_lists": nestedLists
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Update an element in a nested list.
 * 
 * This function demonstrates how to update an element in a nested list
 * using multiple index notations.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} listName - The name of the list attribute
 * @param {number} outerIndex - The index in the outer list
 * @param {number} innerIndex - The index in the inner list
 * @param {any} value - The new value for the element
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateNestedListElement(
  config,
  tableName,
  key,
  listName,
  outerIndex,
  innerIndex,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using multiple index notations
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${listName}[${outerIndex}][${innerIndex}] = :value`,
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}
```
列表操作的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to work with lists in DynamoDB.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "UserProfiles";
  const key = { UserId: "U12345" };
  
  console.log("Demonstrating list operations in DynamoDB");
  
  try {
    // Example 1: Append elements to a list
    console.log("\nExample 1: Appending elements to a list");
    const response1 = await appendToList(
      config,
      tableName,
      key,
      "RecentSearches",
      ["laptop", "headphones", "monitor"]
    );
    
    console.log("Appended to list:", response1.Attributes);
    
    // Example 2: Prepend elements to a list
    console.log("\nExample 2: Prepending elements to a list");
    const response2 = await prependToList(
      config,
      tableName,
      key,
      "RecentSearches",
      ["keyboard", "mouse"]
    );
    
    console.log("Prepended to list:", response2.Attributes);
    
    // Get the current state of the item
    let currentItem = await getItem(config, tableName, key);
    console.log("\nCurrent state of RecentSearches:", currentItem?.RecentSearches);
    
    // Example 3: Update a specific element in a list
    console.log("\nExample 3: Updating a specific element in a list");
    const response3 = await updateListElement(
      config,
      tableName,
      key,
      "RecentSearches",
      0, // Update the first element
      "mechanical keyboard" // New value
    );
    
    console.log("Updated list element:", response3.Attributes);
    
    // Example 4: Remove an element from a list
    console.log("\nExample 4: Removing an element from a list");
    const response4 = await removeListElement(
      config,
      tableName,
      key,
      "RecentSearches",
      2 // Remove the third element
    );
    
    console.log("List after removing element:", response4.Attributes);
    
    // Example 5: Create and concatenate lists
    console.log("\nExample 5: Creating and concatenating lists");
    
    // First, create two separate lists
    await updateWithMultipleActions(
      config,
      tableName,
      key,
      "SET WishList = :wishlist, SavedItems = :saveditems",
      null,
      {
        ":wishlist": ["gaming laptop", "wireless earbuds"],
        ":saveditems": ["smartphone", "tablet"]
      }
    );
    
    // Then, concatenate them
    const response5 = await concatenateLists(
      config,
      tableName,
      key,
      "WishList",
      "SavedItems",
      "AllItems"
    );
    
    console.log("Concatenated lists:", response5.Attributes);
    
    // Example 6: Create a nested list structure
    console.log("\nExample 6: Creating a nested list structure");
    const response6 = await createNestedList(
      config,
      tableName,
      key,
      "Categories",
      [
        ["Electronics", "Computers", "Accessories"],
        ["Books", "Magazines", "E-books"],
        ["Clothing", "Shoes", "Watches"]
      ]
    );
    
    console.log("Created nested list:", response6.Attributes);
    
    // Example 7: Update an element in a nested list
    console.log("\nExample 7: Updating an element in a nested list");
    const response7 = await updateNestedListElement(
      config,
      tableName,
      key,
      "Categories",
      0, // First inner list
      1, // Second element in that list
      "Laptops" // New value
    );
    
    console.log("Updated nested list element:", response7.Attributes);
    
    // Get the final state of the item
    currentItem = await getItem(config, tableName, key);
    console.log("\nFinal state of the item:", JSON.stringify(currentItem, null, 2));
    
    // Explain list operations
    console.log("\nKey points about list operations in DynamoDB:");
    console.log("1. Use list_append to add elements to a list");
    console.log("2. To append elements, use list_append(existingList, newElements)");
    console.log("3. To prepend elements, use list_append(newElements, existingList)");
    console.log("4. Use if_not_exists to handle cases where the list might not exist yet");
    console.log("5. Use index notation (list[0]) to access or update specific elements");
    console.log("6. Use REMOVE with index notation to remove elements from a list");
    console.log("7. Lists can contain elements of different types");
    console.log("8. Lists can be nested (lists of lists)");
    console.log("9. Use multiple index notations (list[0][1]) to access nested list elements");
    
  } catch (error) {
    console.error("Error:", error);
  }
}

/**
 * Helper function for the examples.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} updateExpression - The update expression
 * @param {Object} expressionAttributeNames - Expression attribute name placeholders
 * @param {Object} expressionAttributeValues - Expression attribute value placeholders
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithMultipleActions(
  config,
  tableName,
  key,
  updateExpression,
  expressionAttributeNames,
  expressionAttributeValues
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Prepare the update parameters
  const updateParams = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Add expression attribute names if provided
  if (expressionAttributeNames) {
    updateParams.ExpressionAttributeNames = expressionAttributeNames;
  }
  
  // Add expression attribute values if provided
  if (expressionAttributeValues) {
    updateParams.ExpressionAttributeValues = expressionAttributeValues;
  }
  
  // Execute the update
  const response = await docClient.send(new UpdateCommand(updateParams));
  
  return response;
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 执行映射操作
<a name="dynamodb_Scenario_MapOperations_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中执行映射操作。
+ 在映射结构中添加和更新嵌套属性。
+ 从映射中移除特定字段。
+ 使用深度嵌套的映射属性。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示地图操作 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of updating map attributes in DynamoDB.
 * 
 * This module demonstrates how to update map attributes that may not exist,
 * how to update nested attributes, and how to handle various map update scenarios.
 */

const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Update a map attribute safely, handling the case where the map might not exist.
 * 
 * This function demonstrates using the if_not_exists function to safely update
 * a map attribute that might not exist yet.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} mapName - The name of the map attribute
 * @param {string} mapKey - The key within the map to update
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateMapAttributeSafe(
  config,
  tableName,
  key,
  mapName,
  mapKey,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using SET with if_not_exists
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${mapName}.${mapKey} = :value`,
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    return response;
  } catch (error) {
    // If the error is because the map doesn't exist, create it
    if (error.name === "ValidationException" && 
        error.message.includes("The document path provided in the update expression is invalid")) {
      
      // Create the map with the specified key-value pair
      const createParams = {
        TableName: tableName,
        Key: key,
        UpdateExpression: `SET ${mapName} = :map`,
        ExpressionAttributeValues: {
          ":map": { [mapKey]: value }
        },
        ReturnValues: "UPDATED_NEW"
      };
      
      return await docClient.send(new UpdateCommand(createParams));
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Update a map attribute using the if_not_exists function.
 * 
 * This function demonstrates a more elegant approach using if_not_exists
 * to handle the case where the map doesn't exist yet.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} mapName - The name of the map attribute
 * @param {string} mapKey - The key within the map to update
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateMapAttributeWithIfNotExists(
  config,
  tableName,
  key,
  mapName,
  mapKey,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using SET with if_not_exists
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${mapName} = if_not_exists(${mapName}, :emptyMap), ${mapName}.${mapKey} = :value`,
    ExpressionAttributeValues: {
      ":emptyMap": {},
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Add a value to a deeply nested map, creating parent maps if they don't exist.
 * 
 * This function demonstrates how to update a deeply nested attribute,
 * creating any parent maps that don't exist along the way.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string[]} path - The path to the nested attribute as an array of keys
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function addToNestedMap(
  config,
  tableName,
  key,
  path,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression and expression attribute values
  let updateExpression = "SET";
  const expressionAttributeValues = {};
  
  // For each level in the path, create a map if it doesn't exist
  for (let i = 0; i < path.length; i++) {
    const currentPath = path.slice(0, i + 1).join(".");
    const parentPath = i > 0 ? path.slice(0, i).join(".") : null;
    
    if (parentPath) {
      updateExpression += ` ${parentPath} = if_not_exists(${parentPath}, :emptyMap${i}),`;
      expressionAttributeValues[`:emptyMap${i}`] = {};
    }
  }
  
  // Set the final value
  const fullPath = path.join(".");
  updateExpression += ` ${fullPath} = :value`;
  expressionAttributeValues[":value"] = value;
  
  // Define the update parameters
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Update multiple fields in a map attribute in a single operation.
 * 
 * This function demonstrates how to update multiple fields in a map
 * in a single DynamoDB operation.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} mapName - The name of the map attribute
 * @param {Object} updates - Object containing key-value pairs to update
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateMultipleMapFields(
  config,
  tableName,
  key,
  mapName,
  updates
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression and expression attribute values
  let updateExpression = `SET ${mapName} = if_not_exists(${mapName}, :emptyMap)`;
  const expressionAttributeValues = {
    ":emptyMap": {}
  };
  
  // Add each update to the expression
  Object.entries(updates).forEach(([field, value], index) => {
    updateExpression += `, ${mapName}.${field} = :val${index}`;
    expressionAttributeValues[`:val${index}`] = value;
  });
  
  // Define the update parameters
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}

/**
 * Example of how to use the map attribute update functions.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Users";
  const key = { UserId: "U12345" };
  
  console.log("Demonstrating different approaches to update map attributes in DynamoDB");
  
  try {
    // Example 1: Update a map attribute that might not exist (two-step approach)
    console.log("\nExample 1: Updating a map attribute that might not exist (two-step approach)");
    const response1 = await updateMapAttributeSafe(
      config,
      tableName,
      key,
      "Preferences",
      "Theme",
      "Dark"
    );
    
    console.log("Updated preferences:", response1.Attributes);
    
    // Example 2: Update a map attribute using if_not_exists (elegant approach)
    console.log("\nExample 2: Updating a map attribute using if_not_exists (elegant approach)");
    const response2 = await updateMapAttributeWithIfNotExists(
      config,
      tableName,
      key,
      "Settings",
      "NotificationsEnabled",
      true
    );
    
    console.log("Updated settings:", response2.Attributes);
    
    // Example 3: Update a deeply nested attribute
    console.log("\nExample 3: Updating a deeply nested attribute");
    const response3 = await addToNestedMap(
      config,
      tableName,
      key,
      ["Profile", "Address", "City"],
      "Seattle"
    );
    
    console.log("Updated nested attribute:", response3.Attributes);
    
    // Example 4: Update multiple fields in a map
    console.log("\nExample 4: Updating multiple fields in a map");
    const response4 = await updateMultipleMapFields(
      config,
      tableName,
      key,
      "ContactInfo",
      {
        Email: "user@example.com",
        Phone: "555-123-4567",
        PreferredContact: "Email"
      }
    );
    
    console.log("Updated multiple fields:", response4.Attributes);
    
    // Get the final state of the item
    console.log("\nFinal state of the item:");
    const item = await getItem(config, tableName, key);
    console.log(JSON.stringify(item, null, 2));
    
    // Explain the benefits of different approaches
    console.log("\nKey points about updating map attributes:");
    console.log("1. Use if_not_exists to handle maps that might not exist");
    console.log("2. Multiple updates can be combined in a single operation");
    console.log("3. Deeply nested attributes require creating parent maps");
    console.log("4. DynamoDB expressions are atomic - the entire update succeeds or fails");
    console.log("5. Using a single operation is more efficient than multiple separate updates");
    
  } catch (error) {
    console.error("Error:", error);
  }
}

// Export the functions
module.exports = {
  updateMapAttributeSafe,
  updateMapAttributeWithIfNotExists,
  addToNestedMap,
  updateMultipleMapFields,
  getItem,
  exampleUsage
};

// Run the example if this file is executed directly
if (require.main === module) {
  exampleUsage();
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 执行设置操作
<a name="dynamodb_Scenario_SetOperations_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中执行设置操作。
+ 向设置属性添加元素。
+ 从设置属性中移除元素。
+ 将 ADD 和 DELETE 操作用于设置。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示集合操作 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Add elements to a set attribute.
 * 
 * This function demonstrates using the ADD operation to add elements to a set.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} setName - The name of the set attribute
 * @param {Array} values - The values to add to the set
 * @param {string} setType - The type of set ('string', 'number', or 'binary')
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function addToSet(
  config,
  tableName,
  key,
  setName,
  values,
  setType = 'string'
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create the appropriate set type
  let setValues;
  if (setType === 'string') {
    setValues = new Set(values.map(String));
  } else if (setType === 'number') {
    setValues = new Set(values.map(Number));
  } else if (setType === 'binary') {
    setValues = new Set(values);
  } else {
    throw new Error(`Unsupported set type: ${setType}`);
  }
  
  // Define the update parameters using ADD
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `ADD ${setName} :values`,
    ExpressionAttributeValues: {
      ":values": setValues
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Remove elements from a set attribute.
 * 
 * This function demonstrates using the DELETE operation to remove elements from a set.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} setName - The name of the set attribute
 * @param {Array} values - The values to remove from the set
 * @param {string} setType - The type of set ('string', 'number', or 'binary')
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function removeFromSet(
  config,
  tableName,
  key,
  setName,
  values,
  setType = 'string'
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create the appropriate set type
  let setValues;
  if (setType === 'string') {
    setValues = new Set(values.map(String));
  } else if (setType === 'number') {
    setValues = new Set(values.map(Number));
  } else if (setType === 'binary') {
    setValues = new Set(values);
  } else {
    throw new Error(`Unsupported set type: ${setType}`);
  }
  
  // Define the update parameters using DELETE
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `DELETE ${setName} :values`,
    ExpressionAttributeValues: {
      ":values": setValues
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Create a new set attribute with initial values.
 * 
 * This function demonstrates using the SET operation to create a new set attribute.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} setName - The name of the set attribute
 * @param {Array} values - The initial values for the set
 * @param {string} setType - The type of set ('string', 'number', or 'binary')
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function createSet(
  config,
  tableName,
  key,
  setName,
  values,
  setType = 'string'
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create the appropriate set type
  let setValues;
  if (setType === 'string') {
    setValues = new Set(values.map(String));
  } else if (setType === 'number') {
    setValues = new Set(values.map(Number));
  } else if (setType === 'binary') {
    setValues = new Set(values);
  } else {
    throw new Error(`Unsupported set type: ${setType}`);
  }
  
  // Define the update parameters using SET
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${setName} = :values`,
    ExpressionAttributeValues: {
      ":values": setValues
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Replace an entire set attribute with a new set of values.
 * 
 * This function demonstrates using the SET operation to replace an entire set.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} setName - The name of the set attribute
 * @param {Array} values - The new values for the set
 * @param {string} setType - The type of set ('string', 'number', or 'binary')
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function replaceSet(
  config,
  tableName,
  key,
  setName,
  values,
  setType = 'string'
) {
  // This is the same as createSet, but included for clarity of intent
  return await createSet(config, tableName, key, setName, values, setType);
}

/**
 * Remove the last element from a set and handle the empty set case.
 * 
 * This function demonstrates what happens when you delete the last element of a set.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} setName - The name of the set attribute
 * @returns {Promise<Object>} - The result of the operation
 */
async function removeLastElementFromSet(
  config,
  tableName,
  key,
  setName
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // First, get the current item to check the set
  const currentItem = await getItem(config, tableName, key);
  
  // Check if the set exists and has elements
  if (!currentItem || !currentItem[setName] || currentItem[setName].size === 0) {
    return {
      success: false,
      message: "Set doesn't exist or is already empty",
      item: currentItem
    };
  }
  
  // Get the set values
  const setValues = Array.from(currentItem[setName]);
  
  // If there's only one element left, remove the attribute entirely
  if (setValues.length === 1) {
    // Define the update parameters to remove the attribute
    const params = {
      TableName: tableName,
      Key: key,
      UpdateExpression: `REMOVE ${setName}`,
      ReturnValues: "UPDATED_NEW"
    };
    
    // Perform the update operation
    await docClient.send(new UpdateCommand(params));
    
    return {
      success: true,
      message: "Last element removed, attribute has been deleted",
      removedValue: setValues[0]
    };
  } else {
    // Otherwise, remove just the last element
    // Create a set with just the last element
    const lastElement = setValues[setValues.length - 1];
    const setType = typeof lastElement === 'number' ? 'number' : 'string';
    
    // Remove the last element
    const response = await removeFromSet(
      config,
      tableName,
      key,
      setName,
      [lastElement],
      setType
    );
    
    return {
      success: true,
      message: "Last element removed, set still contains elements",
      removedValue: lastElement,
      remainingSet: response.Attributes[setName]
    };
  }
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}
```
使用集合操作的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to work with sets in DynamoDB.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Users";
  const key = { UserId: "U12345" };
  
  console.log("Demonstrating set operations in DynamoDB");
  
  try {
    // Example 1: Create a string set
    console.log("\nExample 1: Creating a string set");
    const response1 = await createSet(
      config,
      tableName,
      key,
      "Interests",
      ["Reading", "Hiking", "Cooking"],
      "string"
    );
    
    console.log("Created set:", response1.Attributes);
    
    // Example 2: Add elements to a set
    console.log("\nExample 2: Adding elements to a set");
    const response2 = await addToSet(
      config,
      tableName,
      key,
      "Interests",
      ["Photography", "Travel"],
      "string"
    );
    
    console.log("Updated set after adding elements:", response2.Attributes);
    
    // Example 3: Remove elements from a set
    console.log("\nExample 3: Removing elements from a set");
    const response3 = await removeFromSet(
      config,
      tableName,
      key,
      "Interests",
      ["Cooking"],
      "string"
    );
    
    console.log("Updated set after removing elements:", response3.Attributes);
    
    // Example 4: Create a number set
    console.log("\nExample 4: Creating a number set");
    const response4 = await createSet(
      config,
      tableName,
      key,
      "FavoriteNumbers",
      [7, 42, 99],
      "number"
    );
    
    console.log("Created number set:", response4.Attributes);
    
    // Example 5: Replace an entire set
    console.log("\nExample 5: Replacing an entire set");
    const response5 = await replaceSet(
      config,
      tableName,
      key,
      "Interests",
      ["Gaming", "Movies", "Music"],
      "string"
    );
    
    console.log("Replaced set:", response5.Attributes);
    
    // Example 6: Remove the last element from a set
    console.log("\nExample 6: Removing the last element from a set");
    
    // First, create a set with just one element
    await createSet(
      config,
      tableName,
      { UserId: "U67890" },
      "Tags",
      ["LastTag"],
      "string"
    );
    
    // Then, remove the last element
    const response6 = await removeLastElementFromSet(
      config,
      tableName,
      { UserId: "U67890" },
      "Tags"
    );
    
    console.log(response6.message);
    console.log("Removed value:", response6.removedValue);
    
    // Get the final state of the items
    console.log("\nFinal state of the items:");
    const item1 = await getItem(config, tableName, key);
    console.log("User U12345:", JSON.stringify(item1, null, 2));
    
    const item2 = await getItem(config, tableName, { UserId: "U67890" });
    console.log("User U67890:", JSON.stringify(item2, null, 2));
    
    // Explain set operations
    console.log("\nKey points about set operations in DynamoDB:");
    console.log("1. Use ADD to add elements to a set (duplicates are automatically removed)");
    console.log("2. Use DELETE to remove elements from a set");
    console.log("3. Use SET to create a new set or replace an existing one");
    console.log("4. DynamoDB supports three types of sets: string sets, number sets, and binary sets");
    console.log("5. When you delete the last element from a set, the attribute remains as an empty set");
    console.log("6. To remove an empty set, use the REMOVE operation");
    console.log("7. Sets automatically maintain unique values (no duplicates)");
    console.log("8. You cannot mix data types within a set");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 使用批量 PartiQL 语句查询表
<a name="dynamodb_Scenario_PartiQLBatch_javascript_3_topic"></a>

以下代码示例展示了如何：
+ 通过运行多个 SELECT 语句来获取一批项目。
+ 通过运行多个 INSERT 语句来添加一批项目。
+ 通过运行多个 UPDATE 语句来更新一批项目。
+ 通过运行多个 DELETE 语句来删除一批项目。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
执行批处理 PartiQL 语句。  

```
import {
  BillingMode,
  CreateTableCommand,
  DeleteTableCommand,
  DescribeTableCommand,
  DynamoDBClient,
  waitUntilTableExists,
} from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";
import { ScenarioInput } from "@aws-doc-sdk-examples/lib/scenario";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

const log = (msg) => console.log(`[SCENARIO] ${msg}`);
const tableName = "Cities";

export const main = async (confirmAll = false) => {
  /**
   * Delete table if it exists.
   */
  try {
    await client.send(new DescribeTableCommand({ TableName: tableName }));
    // If no error was thrown, the table exists.
    const input = new ScenarioInput(
      "deleteTable",
      `A table named ${tableName} already exists. If you choose not to delete
this table, the scenario cannot continue. Delete it?`,
      { type: "confirm", confirmAll },
    );
    const deleteTable = await input.handle({}, { confirmAll });
    if (deleteTable) {
      await client.send(new DeleteTableCommand({ tableName }));
    } else {
      console.warn(
        "Scenario could not run. Either delete ${tableName} or provide a unique table name.",
      );
      return;
    }
  } catch (caught) {
    if (
      caught instanceof Error &&
      caught.name === "ResourceNotFoundException"
    ) {
      // Do nothing. This means the table is not there.
    } else {
      throw caught;
    }
  }

  /**
   * Create a table.
   */

  log("Creating a table.");
  const createTableCommand = new CreateTableCommand({
    TableName: tableName,
    // This example performs a large write to the database.
    // Set the billing mode to PAY_PER_REQUEST to
    // avoid throttling the large write.
    BillingMode: BillingMode.PAY_PER_REQUEST,
    // Define the attributes that are necessary for the key schema.
    AttributeDefinitions: [
      {
        AttributeName: "name",
        // 'S' is a data type descriptor that represents a number type.
        // For a list of all data type descriptors, see the following link.
        // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Programming.LowLevelAPI.html#Programming.LowLevelAPI.DataTypeDescriptors
        AttributeType: "S",
      },
    ],
    // The KeySchema defines the primary key. The primary key can be
    // a partition key, or a combination of a partition key and a sort key.
    // Key schema design is important. For more info, see
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/best-practices.html
    KeySchema: [{ AttributeName: "name", KeyType: "HASH" }],
  });
  await client.send(createTableCommand);
  log(`Table created: ${tableName}.`);

  /**
   * Wait until the table is active.
   */

  // This polls with DescribeTableCommand until the requested table is 'ACTIVE'.
  // You can't write to a table before it's active.
  log("Waiting for the table to be active.");
  await waitUntilTableExists({ client }, { TableName: tableName });
  log("Table active.");

  /**
   * Insert items.
   */

  log("Inserting cities into the table.");
  const addItemsStatementCommand = new BatchExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.insert.html
    Statements: [
      {
        Statement: `INSERT INTO ${tableName} value {'name':?, 'population':?}`,
        Parameters: ["Alachua", 10712],
      },
      {
        Statement: `INSERT INTO ${tableName} value {'name':?, 'population':?}`,
        Parameters: ["High Springs", 6415],
      },
    ],
  });
  await docClient.send(addItemsStatementCommand);
  log("Cities inserted.");

  /**
   * Select items.
   */

  log("Selecting cities from the table.");
  const selectItemsStatementCommand = new BatchExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.select.html
    Statements: [
      {
        Statement: `SELECT * FROM ${tableName} WHERE name=?`,
        Parameters: ["Alachua"],
      },
      {
        Statement: `SELECT * FROM ${tableName} WHERE name=?`,
        Parameters: ["High Springs"],
      },
    ],
  });
  const selectItemResponse = await docClient.send(selectItemsStatementCommand);
  log(
    `Got cities: ${selectItemResponse.Responses.map(
      (r) => `${r.Item.name} (${r.Item.population})`,
    ).join(", ")}`,
  );

  /**
   * Update items.
   */

  log("Modifying the populations.");
  const updateItemStatementCommand = new BatchExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.update.html
    Statements: [
      {
        Statement: `UPDATE ${tableName} SET population=? WHERE name=?`,
        Parameters: [10, "Alachua"],
      },
      {
        Statement: `UPDATE ${tableName} SET population=? WHERE name=?`,
        Parameters: [5, "High Springs"],
      },
    ],
  });
  await docClient.send(updateItemStatementCommand);
  log("Updated cities.");

  /**
   * Delete the items.
   */

  log("Deleting the cities.");
  const deleteItemStatementCommand = new BatchExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.delete.html
    Statements: [
      {
        Statement: `DELETE FROM ${tableName} WHERE name=?`,
        Parameters: ["Alachua"],
      },
      {
        Statement: `DELETE FROM ${tableName} WHERE name=?`,
        Parameters: ["High Springs"],
      },
    ],
  });
  await docClient.send(deleteItemStatementCommand);
  log("Cities deleted.");

  /**
   * Delete the table.
   */

  log("Deleting the table.");
  const deleteTableCommand = new DeleteTableCommand({ TableName: tableName });
  await client.send(deleteTableCommand);
  log("Table deleted.");
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)*中的。

### 使用 PartiQL 来查询表
<a name="dynamodb_Scenario_PartiQLSingle_javascript_3_topic"></a>

以下代码示例展示了如何：
+ 通过运行 SELECT 语句来获取项目。
+ 通过运行 INSERT 语句来添加项目。
+ 通过运行 UPDATE 语句来更新项目。
+ 通过运行 DELETE 语句来删除项目。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在 [AWS 代码示例存储库](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/dynamodb#code-examples)中查找完整示例，了解如何进行设置和运行。
执行单个 PartiQL 语句。  

```
import {
  BillingMode,
  CreateTableCommand,
  DeleteTableCommand,
  DescribeTableCommand,
  DynamoDBClient,
  waitUntilTableExists,
} from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  ExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";
import { ScenarioInput } from "@aws-doc-sdk-examples/lib/scenario";

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

const log = (msg) => console.log(`[SCENARIO] ${msg}`);
const tableName = "SingleOriginCoffees";

export const main = async (confirmAll = false) => {
  /**
   * Delete table if it exists.
   */
  try {
    await client.send(new DescribeTableCommand({ TableName: tableName }));
    // If no error was thrown, the table exists.
    const input = new ScenarioInput(
      "deleteTable",
      `A table named ${tableName} already exists. If you choose not to delete
this table, the scenario cannot continue. Delete it?`,
      { type: "confirm", confirmAll },
    );
    const deleteTable = await input.handle({});
    if (deleteTable) {
      await client.send(new DeleteTableCommand({ tableName }));
    } else {
      console.warn(
        "Scenario could not run. Either delete ${tableName} or provide a unique table name.",
      );
      return;
    }
  } catch (caught) {
    if (
      caught instanceof Error &&
      caught.name === "ResourceNotFoundException"
    ) {
      // Do nothing. This means the table is not there.
    } else {
      throw caught;
    }
  }

  /**
   * Create a table.
   */

  log("Creating a table.");
  const createTableCommand = new CreateTableCommand({
    TableName: tableName,
    // This example performs a large write to the database.
    // Set the billing mode to PAY_PER_REQUEST to
    // avoid throttling the large write.
    BillingMode: BillingMode.PAY_PER_REQUEST,
    // Define the attributes that are necessary for the key schema.
    AttributeDefinitions: [
      {
        AttributeName: "varietal",
        // 'S' is a data type descriptor that represents a number type.
        // For a list of all data type descriptors, see the following link.
        // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Programming.LowLevelAPI.html#Programming.LowLevelAPI.DataTypeDescriptors
        AttributeType: "S",
      },
    ],
    // The KeySchema defines the primary key. The primary key can be
    // a partition key, or a combination of a partition key and a sort key.
    // Key schema design is important. For more info, see
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/best-practices.html
    KeySchema: [{ AttributeName: "varietal", KeyType: "HASH" }],
  });
  await client.send(createTableCommand);
  log(`Table created: ${tableName}.`);

  /**
   * Wait until the table is active.
   */

  // This polls with DescribeTableCommand until the requested table is 'ACTIVE'.
  // You can't write to a table before it's active.
  log("Waiting for the table to be active.");
  await waitUntilTableExists({ client }, { TableName: tableName });
  log("Table active.");

  /**
   * Insert an item.
   */

  log("Inserting a coffee into the table.");
  const addItemStatementCommand = new ExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.insert.html
    Statement: `INSERT INTO ${tableName} value {'varietal':?, 'profile':?}`,
    Parameters: ["arabica", ["chocolate", "floral"]],
  });
  await client.send(addItemStatementCommand);
  log("Coffee inserted.");

  /**
   * Select an item.
   */

  log("Selecting the coffee from the table.");
  const selectItemStatementCommand = new ExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.select.html
    Statement: `SELECT * FROM ${tableName} WHERE varietal=?`,
    Parameters: ["arabica"],
  });
  const selectItemResponse = await docClient.send(selectItemStatementCommand);
  log(`Got coffee: ${JSON.stringify(selectItemResponse.Items[0])}`);

  /**
   * Update the item.
   */

  log("Add a flavor profile to the coffee.");
  const updateItemStatementCommand = new ExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.update.html
    Statement: `UPDATE ${tableName} SET profile=list_append(profile, ?) WHERE varietal=?`,
    Parameters: [["fruity"], "arabica"],
  });
  await client.send(updateItemStatementCommand);
  log("Updated coffee");

  /**
   * Delete the item.
   */

  log("Deleting the coffee.");
  const deleteItemStatementCommand = new ExecuteStatementCommand({
    // https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.delete.html
    Statement: `DELETE FROM ${tableName} WHERE varietal=?`,
    Parameters: ["arabica"],
  });
  await docClient.send(deleteItemStatementCommand);
  log("Coffee deleted.");

  /**
   * Delete the table.
   */

  log("Deleting the table.");
  const deleteTableCommand = new DeleteTableCommand({ TableName: tableName });
  await client.send(deleteTableCommand);
  log("Table deleted.");
};
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)*中的。

### 使用全局二级索引查询表
<a name="dynamodb_Scenarios_QueryWithGlobalSecondaryIndex_javascript_3_topic"></a>

以下代码示例演示如何使用全局二级索引来查询表。
+ 使用 DynamoDB 表的主键查询该表。
+ 查询全局二级索引（GSI）以获取其它访问模式。
+ 比较表查询和 GSI 查询。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用主键查询 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table using the primary key
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} userId - The user ID to query by (partition key)
 * @returns {Promise<Object>} - The query response
 */
async function queryTable(
  config,
  tableName,
  userId
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input for the base table
    const input = {
      TableName: tableName,
      KeyConditionExpression: "user_id = :userId",
      ExpressionAttributeValues: {
        ":userId": { S: userId }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying table: ${error}`);
    throw error;
  }
}
```
使用查询 DynamoDB 全球二级索引 (GSI)。 适用于 JavaScript 的 AWS SDK  

```
/**
 * Queries a DynamoDB Global Secondary Index (GSI)
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} indexName - The name of the GSI to query
 * @param {string} gameId - The game ID to query by (GSI partition key)
 * @returns {Promise<Object>} - The query response
 */
async function queryGSI(
  config,
  tableName,
  indexName,
  gameId
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input for the GSI
    const input = {
      TableName: tableName,
      IndexName: indexName,
      KeyConditionExpression: "game_id = :gameId",
      ExpressionAttributeValues: {
        ":gameId": { S: gameId }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying GSI: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用 begins\$1with 条件查询表
<a name="dynamodb_Scenarios_QueryWithBeginsWithCondition_javascript_3_topic"></a>

以下代码示例演示如何使用 begins\$1with 条件来查询表。
+ 在键条件表达式中使用 begins\$1with 函数。
+ 根据排序键中的前缀模式筛选项目。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 适用于 JavaScript 的 AWS SDK通过排序键上的 begins\$1with 条件查询 DynamoDB 表。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table for items where the sort key begins with a specific prefix
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {string} sortKeyName - The name of the sort key
 * @param {string} prefix - The prefix to match at the beginning of the sort key
 * @returns {Promise<Object>} - The query response
 */
async function queryWithBeginsWith(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  sortKeyName,
  prefix
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue AND begins_with(#sk, :prefix)",
      ExpressionAttributeNames: {
        "#pk": partitionKeyName,
        "#sk": sortKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":prefix": { S: prefix }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with begins_with: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用日期范围查询表
<a name="dynamodb_Scenarios_QueryWithDateRange_javascript_3_topic"></a>

以下代码示例演示如何使用排序键中的日期范围来查询表。
+ 查询特定日期范围内的项目。
+ 对日期格式的排序键使用比较运算符。

**适用于 JavaScript (v3) 的软件开发工具包**  
在 DynamoDB 表中查询 DynamoDB 表中是否有某个日期范围内的项目。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table for items within a specific date range on the sort key
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {string} sortKeyName - The name of the sort key (must be a date/time attribute)
 * @param {Date} startDate - The start date for the range query
 * @param {Date} endDate - The end date for the range query
 * @returns {Promise<Object>} - The query response
 */
async function queryByDateRangeOnSortKey(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  sortKeyName,
  startDate,
  endDate
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Format dates as ISO strings for DynamoDB
    const formattedStartDate = startDate.toISOString();
    const formattedEndDate = endDate.toISOString();

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: '#pk = :pkValue AND #sk BETWEEN :startDate AND :endDate',
      ExpressionAttributeNames: {
        "#pk": partitionKeyName,
        "#sk": sortKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":startDate": { S: formattedStartDate },
        ":endDate": { S: formattedEndDate }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying by date range on sort key: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用复杂的筛选表达式查询表
<a name="dynamodb_Scenarios_QueryWithComplexFilter_javascript_3_topic"></a>

以下代码示例演示如何使用复杂的筛选表达式来查询表。
+ 将复杂的筛选表达式应用于查询结果。
+ 使用逻辑运算符组合条件。
+ 根据非键属性筛选项目。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用复杂筛选表达式查询 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with a complex filter expression
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {number|string} minViews - Minimum number of views for filtering
 * @param {number|string} minReplies - Minimum number of replies for filtering
 * @param {string} requiredTag - Tag that must be present in the item's tags set
 * @returns {Promise<Object>} - The query response
 */
async function queryWithComplexFilter(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  minViews,
  minReplies,
  requiredTag
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue",
      FilterExpression: "views >= :minViews AND replies >= :minReplies AND contains(tags, :tag)",
      ExpressionAttributeNames: {
        "#pk": partitionKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":minViews": { N: minViews.toString() },
        ":minReplies": { N: minReplies.toString() },
        ":tag": { S: requiredTag }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with complex filter: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用动态筛选表达式查询表
<a name="dynamodb_Scenarios_QueryWithDynamicFilter_javascript_3_topic"></a>

以下代码示例演示如何使用动态筛选表达式来查询表。
+ 在运行时动态构建筛选表达式。
+ 根据用户输入或应用程序状态构造筛选条件。
+ 有条件地添加或移除筛选条件。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用动态构造的筛选表达式查询 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

async function queryWithDynamicFilter(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  sortKeyName,
  sortKeyValue,
  filterParams = {}
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Initialize filter expression components
    let filterExpressions = [];
    const expressionAttributeValues = {
      ":pkValue": { S: partitionKeyValue },
      ":skValue": { S: sortKeyValue }
    };
    const expressionAttributeNames = {
      "#pk": partitionKeyName,
      "#sk": sortKeyName
    };

    // Add status filter if provided
    if (filterParams.status) {
      filterExpressions.push("status = :status");
      expressionAttributeValues[":status"] = { S: filterParams.status };
    }

    // Add minimum views filter if provided
    if (filterParams.minViews !== undefined) {
      filterExpressions.push("views >= :minViews");
      expressionAttributeValues[":minViews"] = { N: filterParams.minViews.toString() };
    }

    // Add author filter if provided
    if (filterParams.author) {
      filterExpressions.push("author = :author");
      expressionAttributeValues[":author"] = { S: filterParams.author };
    }

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue AND #sk = :skValue"
    };

    // Add filter expression if any filters were provided
    if (filterExpressions.length > 0) {
      input.FilterExpression = filterExpressions.join(" AND ");
    }

    // Add expression attribute names and values
    input.ExpressionAttributeNames = expressionAttributeNames;
    input.ExpressionAttributeValues = expressionAttributeValues;

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with dynamic filter: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用嵌套属性查询表
<a name="dynamodb_Scenarios_QueryWithNestedAttributes_javascript_3_topic"></a>

以下代码示例演示如何使用嵌套属性来查询表。
+ 按 DynamoDB 项目中的嵌套属性进行访问和筛选。
+ 使用文档路径表达式来引用嵌套元素。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用查询带有嵌套属性的 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table filtering on a nested attribute
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} productId - The product ID to query by (partition key)
 * @param {string} category - The category to filter by (nested attribute)
 * @returns {Promise<Object>} - The query response
 */
async function queryWithNestedAttribute(
  config,
  tableName,
  productId,
  category
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "product_id = :productId",
      FilterExpression: "details.category = :category",
      ExpressionAttributeValues: {
        ":productId": { S: productId },
        ":category": { S: category }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with nested attribute: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 通过分区查询表
<a name="dynamodb_Scenarios_QueryWithPagination_javascript_3_topic"></a>

以下代码示例演示如何使用分区来查询表。
+ 为 DynamoDB 查询结果实现分页。
+ 使用检 LastEvaluatedKey 索后续页面。
+ 使用 Limit 参数控制每页项目数。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用分页查询 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
/**
 * Example demonstrating how to handle large query result sets in DynamoDB using pagination
 * 
 * This example shows:
 * - How to use pagination to handle large result sets
 * - How to use LastEvaluatedKey to retrieve the next page of results
 * - How to construct subsequent query requests using ExclusiveStartKey
 */
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with pagination to handle large result sets
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {number} pageSize - Number of items per page
 * @returns {Promise<Array>} - All items from the query
 */
async function queryWithPagination(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  pageSize = 25
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);
    
    // Initialize variables for pagination
    let lastEvaluatedKey = undefined;
    const allItems = [];
    let pageCount = 0;
    
    // Loop until all pages are retrieved
    do {
      // Construct the query input
      const input = {
        TableName: tableName,
        KeyConditionExpression: "#pk = :pkValue",
        Limit: pageSize,
        ExpressionAttributeNames: {
          "#pk": partitionKeyName
        },
        ExpressionAttributeValues: {
          ":pkValue": { S: partitionKeyValue }
        }
      };
      
      // Add ExclusiveStartKey if we have a LastEvaluatedKey from a previous query
      if (lastEvaluatedKey) {
        input.ExclusiveStartKey = lastEvaluatedKey;
      }
      
      // Execute the query
      const command = new QueryCommand(input);
      const response = await client.send(command);
      
      // Process the current page of results
      pageCount++;
      console.log(`Processing page ${pageCount} with ${response.Items.length} items`);
      
      // Add the items from this page to our collection
      if (response.Items && response.Items.length > 0) {
        allItems.push(...response.Items);
      }
      
      // Get the LastEvaluatedKey for the next page
      lastEvaluatedKey = response.LastEvaluatedKey;
      
    } while (lastEvaluatedKey); // Continue until there are no more pages
    
    console.log(`Query complete. Retrieved ${allItems.length} items in ${pageCount} pages.`);
    return allItems;
  } catch (error) {
    console.error(`Error querying with pagination: ${error}`);
    throw error;
  }
}

/**
 * Example usage:
 * 
 * // Query all items in the "AWS DynamoDB" forum with pagination
 * const allItems = await queryWithPagination(
 *   { region: "us-west-2" },
 *   "ForumThreads",
 *   "ForumName",
 *   "AWS DynamoDB",
 *   25 // 25 items per page
 * );
 * 
 * console.log(`Total items retrieved: ${allItems.length}`);
 * 
 * // Notes on pagination:
 * // - LastEvaluatedKey contains the primary key of the last evaluated item
 * // - When LastEvaluatedKey is undefined/null, there are no more items to retrieve
 * // - ExclusiveStartKey tells DynamoDB where to start the next page
 * // - Pagination helps manage memory usage for large result sets
 * // - Each page requires a separate network request to DynamoDB
 */

module.exports = { queryWithPagination };
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 通过强一致性读取查询表
<a name="dynamodb_Scenarios_QueryWithStronglyConsistentReads_javascript_3_topic"></a>

以下代码示例演示如何使用强一致性读取来查询表。
+ 为 DynamoDB 查询配置一致性级别。
+ 使用强一致性读取来获取最多的 up-to-date数据。
+ 了解最终一致性和强一致性之间的权衡。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用查询具有可配置读取一致性的 DynamoDB 表。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table with configurable read consistency
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {boolean} useConsistentRead - Whether to use strongly consistent reads
 * @returns {Promise<Object>} - The query response
 */
async function queryWithConsistentRead(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  useConsistentRead = false
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: "#pk = :pkValue",
      ExpressionAttributeNames: {
        "#pk": partitionKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue }
      },
      ConsistentRead: useConsistentRead
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying with consistent read: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用 PartiQL SELECT 查询数据
<a name="dynamodb_PartiQLSelect_javascript_3_topic"></a>

以下代码示例演示如何使用 PartiQL SELECT 语句查询数据。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用带有的 PartiQL SELECT 语句查询 DynamoDB 表中的项目。 适用于 JavaScript 的 AWS SDK  

```
/**
 * This example demonstrates how to query items from a DynamoDB table using PartiQL.
 * It shows different ways to select data with various index types.
 */
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  ExecuteStatementCommand,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

/**
 * Select all items from a DynamoDB table using PartiQL.
 * Note: This should be used with caution on large tables.
 * 
 * @param tableName - The name of the DynamoDB table
 * @returns The response from the ExecuteStatementCommand
 */
export const selectAllItems = async (tableName: string) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}"`,
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Items retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving items:", err);
    throw err;
  }
};

/**
 * Select an item by its primary key using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @returns The response from the ExecuteStatementCommand
 */
export const selectItemByPartitionKey = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}" WHERE ${partitionKeyName} = ?`,
    Parameters: [partitionKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving item:", err);
    throw err;
  }
};

/**
 * Select an item by its composite key (partition key + sort key) using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param sortKeyName - The name of the sort key attribute
 * @param sortKeyValue - The value of the sort key
 * @returns The response from the ExecuteStatementCommand
 */
export const selectItemByCompositeKey = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  sortKeyName: string,
  sortKeyValue: string | number
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}" WHERE ${partitionKeyName} = ? AND ${sortKeyName} = ?`,
    Parameters: [partitionKeyValue, sortKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving item:", err);
    throw err;
  }
};

/**
 * Select items using a filter condition with PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param filterAttribute - The attribute to filter on
 * @param filterValue - The value to filter by
 * @returns The response from the ExecuteStatementCommand
 */
export const selectItemsWithFilter = async (
  tableName: string,
  filterAttribute: string,
  filterValue: string | number
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}" WHERE ${filterAttribute} = ?`,
    Parameters: [filterValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Items retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving items:", err);
    throw err;
  }
};

/**
 * Select items using a begins_with function for prefix matching.
 * This is useful for querying hierarchical data.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param attributeName - The attribute to check for prefix
 * @param prefix - The prefix to match
 * @returns The response from the ExecuteStatementCommand
 */
export const selectItemsByPrefix = async (
  tableName: string,
  attributeName: string,
  prefix: string
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}" WHERE begins_with(${attributeName}, ?)`,
    Parameters: [prefix],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Items retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving items:", err);
    throw err;
  }
};

/**
 * Select items using a between condition for range queries.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param attributeName - The attribute to check for range
 * @param startValue - The start value of the range
 * @param endValue - The end value of the range
 * @returns The response from the ExecuteStatementCommand
 */
export const selectItemsByRange = async (
  tableName: string,
  attributeName: string,
  startValue: number | string,
  endValue: number | string
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `SELECT * FROM "${tableName}" WHERE ${attributeName} BETWEEN ? AND ?`,
    Parameters: [startValue, endValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Items retrieved successfully");
    return data;
  } catch (err) {
    console.error("Error retrieving items:", err);
    throw err;
  }
};

/**
 * Example usage showing how to select items with different index types
 */
export const selectExamples = async () => {
  // Select all items from a table (use with caution on large tables)
  await selectAllItems("UsersTable");

  // Select by partition key (simple primary key)
  await selectItemByPartitionKey("UsersTable", "userId", "user123");

  // Select by composite key (partition key + sort key)
  await selectItemByCompositeKey("OrdersTable", "orderId", "order456", "productId", "prod789");

  // Select with a filter condition (can use any attribute)
  await selectItemsWithFilter("UsersTable", "userType", "premium");

  // Select items with a prefix (useful for hierarchical data)
  await selectItemsByPrefix("ProductsTable", "category", "electronics");

  // Select items within a range (useful for numeric or date ranges)
  await selectItemsByRange("OrdersTable", "orderDate", "2023-01-01", "2023-12-31");
};
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)
  + [ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)

### 查询 TTL 项目
<a name="dynamodb_QueryFilteredTTL_javascript_3_topic"></a>

以下代码示例演示如何查询 TTL 项目。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用查询筛选表达式以收集 DynamoDB 表中的 TTL 项目。 适用于 JavaScript 的 AWS SDK  

```
import { DynamoDBClient, QueryCommand } from "@aws-sdk/client-dynamodb";
import { marshall, unmarshall } from "@aws-sdk/util-dynamodb";

export const queryFiltered = async (tableName, primaryKey, region = 'us-east-1') => {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const currentTime = Math.floor(Date.now() / 1000);

    const params = {
        TableName: tableName,
        KeyConditionExpression: "#pk = :pk",
        FilterExpression: "#ea > :ea",
        ExpressionAttributeNames: {
            "#pk": "primaryKey",
            "#ea": "expireAt"
        },
        ExpressionAttributeValues: marshall({
            ":pk": primaryKey,
            ":ea": currentTime
        })
    };

    try {
        const { Items } = await client.send(new QueryCommand(params));
        Items.forEach(item => {
            console.log(unmarshall(item))
        });
        return Items;
    } catch (err) {
        console.error(`Error querying items: ${err}`);
        throw err;
    }
}

// Example usage (commented out for testing)
// queryFiltered('your-table-name', 'your-partition-key-value');
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 使用日期和时间模式查询表
<a name="dynamodb_Scenario_DateTimeQueries_javascript_3_topic"></a>

以下代码示例演示如何使用日期和时间模式来查询表。
+ 在 DynamoDB 中存储和查询 date/time 值。
+ 使用排序键实现日期范围查询。
+ 对日期字符串格式化以进行有效查询。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用排序键中的日期范围进行查询 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table for items within a specific date range on the sort key
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {string} sortKeyName - The name of the sort key (must be a date/time attribute)
 * @param {Date} startDate - The start date for the range query
 * @param {Date} endDate - The end date for the range query
 * @returns {Promise<Object>} - The query response
 */
async function queryByDateRangeOnSortKey(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  sortKeyName,
  startDate,
  endDate
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Format dates as ISO strings for DynamoDB
    const formattedStartDate = startDate.toISOString();
    const formattedEndDate = endDate.toISOString();

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: '#pk = :pkValue AND #sk BETWEEN :startDate AND :endDate',
      ExpressionAttributeNames: {
        "#pk": partitionKeyName,
        "#sk": sortKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":startDate": { S: formattedStartDate },
        ":endDate": { S: formattedEndDate }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying by date range on sort key: ${error}`);
    throw error;
  }
}
```
使用日期时间变量进行查询。 适用于 JavaScript 的 AWS SDK  

```
const { DynamoDBClient, QueryCommand } = require("@aws-sdk/client-dynamodb");

/**
 * Queries a DynamoDB table for items within a specific date range
 * 
 * @param {Object} config - AWS SDK configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key
 * @param {string} partitionKeyValue - The value of the partition key
 * @param {string} dateKeyName - The name of the date attribute to filter on
 * @param {Date} startDate - The start date for the range query
 * @param {Date} endDate - The end date for the range query
 * @returns {Promise<Object>} - The query response
 */
async function queryByDateRange(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  dateKeyName,
  startDate,
  endDate
) {
  try {
    // Create DynamoDB client
    const client = new DynamoDBClient(config);

    // Format dates as ISO strings for DynamoDB
    const formattedStartDate = startDate.toISOString();
    const formattedEndDate = endDate.toISOString();

    // Construct the query input
    const input = {
      TableName: tableName,
      KeyConditionExpression: `#pk = :pkValue AND #dateAttr BETWEEN :startDate AND :endDate`,
      ExpressionAttributeNames: {
        "#pk": partitionKeyName,
        "#dateAttr": dateKeyName
      },
      ExpressionAttributeValues: {
        ":pkValue": { S: partitionKeyValue },
        ":startDate": { S: formattedStartDate },
        ":endDate": { S: formattedEndDate }
      }
    };

    // Execute the query
    const command = new QueryCommand(input);
    return await client.send(command);
  } catch (error) {
    console.error(`Error querying by date range: ${error}`);
    throw error;
  }
}
```
+  有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

### 了解更新表达式顺序
<a name="dynamodb_Scenario_UpdateExpressionOrder_javascript_3_topic"></a>

以下代码示例演示如何了解更新表达式顺序。
+ 了解 DynamoDB 如何处理更新表达式。
+ 了解更新表达式中的操作顺序。
+ 通过了解表达式求值来避免意外结果。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示更新表达式顺序 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand,
  PutCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Update an item with multiple actions in a single update expression.
 * 
 * This function demonstrates how to use multiple actions in a single update expression
 * and how DynamoDB processes these actions.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {string} updateExpression - The update expression with multiple actions
 * @param {Object} [expressionAttributeNames] - Expression attribute name placeholders
 * @param {Object} [expressionAttributeValues] - Expression attribute value placeholders
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithMultipleActions(
  config,
  tableName,
  key,
  updateExpression,
  expressionAttributeNames,
  expressionAttributeValues
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Prepare the update parameters
  const updateParams = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Add expression attribute names if provided
  if (expressionAttributeNames) {
    updateParams.ExpressionAttributeNames = expressionAttributeNames;
  }
  
  // Add expression attribute values if provided
  if (expressionAttributeValues) {
    updateParams.ExpressionAttributeValues = expressionAttributeValues;
  }
  
  // Execute the update
  const response = await docClient.send(new UpdateCommand(updateParams));
  
  return response;
}

/**
 * Demonstrate that variables hold copies of existing values before modifications.
 * 
 * This function creates an item with initial values, then updates it with an expression
 * that uses the values of attributes before they are modified in the same expression.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateValueCopying(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = { ...key, a: 1, b: 2, c: 3 };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with an expression that uses values before they are modified
  // This expression removes 'a', then sets 'b' to the value of 'a', and 'c' to the value of 'b'
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: "REMOVE a SET b = a, c = b",
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}

/**
 * Demonstrate the order in which different action types are processed.
 * 
 * This function creates an item with initial values, then updates it with an expression
 * that includes multiple action types (SET, REMOVE, ADD, DELETE) to show the order
 * in which they are processed.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateActionOrder(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = {
    ...key,
    counter: 10,
    set_attr: new Set(["A", "B", "C"]),
    to_remove: "This will be removed",
    to_modify: "Original value"
  };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with multiple action types
  // The actions will be processed in this order: REMOVE, SET, ADD, DELETE
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: "REMOVE to_remove SET to_modify = :new_value ADD counter :increment DELETE set_attr :elements",
    ExpressionAttributeValues: {
      ":new_value": "Updated value",
      ":increment": 5,
      ":elements": new Set(["B"])
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}

/**
 * Update multiple attributes with a single SET action.
 * 
 * This function demonstrates how to update multiple attributes in a single SET action,
 * which is more efficient than using multiple separate update operations.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {Object} attributes - The attributes to update and their new values
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithMultipleSetActions(
  config,
  tableName,
  key,
  attributes
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression and expression attribute values
  let updateExpression = "SET ";
  const expressionAttributeValues = {};
  
  // Add each attribute to the update expression
  Object.entries(attributes).forEach(([attrName, attrValue], index) => {
    const valuePlaceholder = `:val${index}`;
    
    if (index > 0) {
      updateExpression += ", ";
    }
    updateExpression += `${attrName} = ${valuePlaceholder}`;
    
    expressionAttributeValues[valuePlaceholder] = attrValue;
  });
  
  // Execute the update
  const response = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  }));
  
  return response;
}

/**
 * Update an attribute with a value from another attribute or a default value.
 * 
 * This function demonstrates how to use if_not_exists to conditionally copy a value
 * from one attribute to another, or use a default value if the source doesn't exist.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {string} sourceAttribute - The attribute to copy the value from
 * @param {string} targetAttribute - The attribute to update
 * @param {any} defaultValue - The default value to use if the source attribute doesn't exist
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithConditionalValueCopying(
  config,
  tableName,
  key,
  sourceAttribute,
  targetAttribute,
  defaultValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Use if_not_exists to conditionally copy the value
  const response = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${targetAttribute} = if_not_exists(${sourceAttribute}, :default)`,
    ExpressionAttributeValues: {
      ":default": defaultValue
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  return response;
}

/**
 * Demonstrate complex update expressions with multiple operations on the same attribute.
 * 
 * This function shows how DynamoDB processes multiple operations on the same attribute
 * in a single update expression.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateMultipleOperationsOnSameAttribute(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = {
    ...key,
    counter: 10,
    list_attr: [1, 2, 3],
    map_attr: {
      nested1: "value1",
      nested2: "value2"
    }
  };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with multiple operations on the same attributes
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: `
      SET counter = counter + :inc1,
          counter = counter + :inc2,
          map_attr.nested1 = :new_val1,
          map_attr.nested3 = :new_val3,
          list_attr[0] = list_attr[1],
          list_attr[1] = list_attr[2]
    `,
    ExpressionAttributeValues: {
      ":inc1": 5,
      ":inc2": 3,
      ":new_val1": "updated_value1",
      ":new_val3": "new_value3"
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}
```
使用更新表达式顺序的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to use update expression order of operations in DynamoDB.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "OrderProcessing";
  
  console.log("Demonstrating update expression order of operations in DynamoDB");
  
  try {
    // Example 1: Demonstrating value copying in update expressions
    console.log("\nExample 1: Demonstrating value copying in update expressions");
    const results1 = await demonstrateValueCopying(
      config,
      tableName,
      { OrderId: "order123" }
    );
    
    console.log("Initial state:", JSON.stringify(results1.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results1.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results1.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The initial state had a=1, b=2, c=3");
    console.log("2. The update expression 'REMOVE a SET b = a, c = b' did the following:");
    console.log("   - Copied the value of 'a' (which was 1) to be used for 'b'");
    console.log("   - Copied the value of 'b' (which was 2) to be used for 'c'");
    console.log("   - Removed the attribute 'a'");
    console.log("3. The final state has b=1, c=2, and 'a' is removed");
    console.log("4. This demonstrates that DynamoDB uses the values of attributes as they were BEFORE any modifications");
    
    // Example 2: Demonstrating the order of different action types
    console.log("\nExample 2: Demonstrating the order of different action types");
    const results2 = await demonstrateActionOrder(
      config,
      tableName,
      { OrderId: "order456" }
    );
    
    console.log("Initial state:", JSON.stringify(results2.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results2.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results2.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The update expression contained multiple action types: REMOVE, SET, ADD, DELETE");
    console.log("2. DynamoDB processes these actions in this order: REMOVE, SET, ADD, DELETE");
    console.log("3. First, 'to_remove' was removed");
    console.log("4. Then, 'to_modify' was set to a new value");
    console.log("5. Next, 'counter' was incremented by 5");
    console.log("6. Finally, 'B' was removed from the set attribute");
    
    // Example 3: Updating multiple attributes in a single SET action
    console.log("\nExample 3: Updating multiple attributes in a single SET action");
    const response3 = await updateWithMultipleSetActions(
      config,
      tableName,
      { OrderId: "order789" },
      {
        Status: "Shipped",
        ShippingDate: "2025-05-28",
        TrackingNumber: "1Z999AA10123456784"
      }
    );
    
    console.log("Multiple attributes updated successfully:", JSON.stringify(response3.Attributes, null, 2));
    
    // Example 4: Conditional value copying with if_not_exists
    console.log("\nExample 4: Conditional value copying with if_not_exists");
    const response4 = await updateWithConditionalValueCopying(
      config,
      tableName,
      { OrderId: "order101" },
      "PreferredShippingMethod",
      "ShippingMethod",
      "Standard"
    );
    
    console.log("Conditional value copying result:", JSON.stringify(response4.Attributes, null, 2));
    
    // Example 5: Multiple operations on the same attribute
    console.log("\nExample 5: Multiple operations on the same attribute");
    const results5 = await demonstrateMultipleOperationsOnSameAttribute(
      config,
      tableName,
      { OrderId: "order202" }
    );
    
    console.log("Initial state:", JSON.stringify(results5.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results5.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results5.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The counter was incremented twice (first by 5, then by 3) for a total of +8");
    console.log("2. The map attribute had one value updated and a new nested attribute added");
    console.log("3. The list attribute had values shifted (value at index 1 moved to index 0, value at index 2 moved to index 1)");
    console.log("4. All operations within the SET action are processed from left to right");
    
    // Key points about update expression order of operations
    console.log("\nKey Points About Update Expression Order of Operations:");
    console.log("1. Variables in expressions hold copies of attribute values as they existed BEFORE any modifications");
    console.log("2. Multiple actions in an update expression are processed in this order: REMOVE, SET, ADD, DELETE");
    console.log("3. Within each action type, operations are processed from left to right");
    console.log("4. You can reference the same attribute multiple times in an expression");
    console.log("5. You can use if_not_exists() to conditionally set values based on attribute existence");
    console.log("6. Using a single update expression with multiple actions is more efficient than multiple separate updates");
    console.log("7. The update expression is atomic - either all actions succeed or none do");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 更新表的热吞吐量设置
<a name="dynamodb_UpdateTableWarmThroughput_javascript_3_topic"></a>

以下代码示例演示如何更新表的热吞吐量设置。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用 适用于 JavaScript 的 AWS SDK更新现有 DynamoDB 表上的热吞吐量设置。  

```
import { DynamoDBClient, UpdateTableCommand } from "@aws-sdk/client-dynamodb";

export async function updateDynamoDBTableWarmThroughput(
  tableName,
  tableReadUnits,
  tableWriteUnits,
  gsiName,
  gsiReadUnits,
  gsiWriteUnits,
  region = "us-east-1"
) {
  try {
    const ddbClient = new DynamoDBClient({ region: region });

    // Construct the update table request
    const updateTableRequest = {
      TableName: tableName,
      GlobalSecondaryIndexUpdates: [
        {
            Update: {
                IndexName: gsiName,
                WarmThroughput: {
                    ReadUnitsPerSecond: gsiReadUnits,
                    WriteUnitsPerSecond: gsiWriteUnits,
                },
            },
        },
      ],
      WarmThroughput: {
          ReadUnitsPerSecond: tableReadUnits,
          WriteUnitsPerSecond: tableWriteUnits,
      },
    };

    const command = new UpdateTableCommand(updateTableRequest);
    const response = await ddbClient.send(command);
    console.log(`Table updated successfully! Response: ${JSON.stringify(response)}`);
    return response;
  } catch (error) {
    console.error(`Error updating table: ${error}`);
    throw error;
  }
}

// Example usage (commented out for testing)
/*
updateDynamoDBTableWarmThroughput(
  'example-table',
  5, 5,
  'example-index',
  2, 2
);
*/
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateTable](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateTableCommand)*中的。

### 更新项目的 TTL
<a name="dynamodb_UpdateItemTTL_javascript_3_topic"></a>

以下代码示例演示如何更新项目的 TTL。

**适用于 JavaScript (v3) 的软件开发工具包**  

```
import { DynamoDBClient, UpdateItemCommand } from "@aws-sdk/client-dynamodb";
import { marshall, unmarshall } from "@aws-sdk/util-dynamodb";

export const updateItem = async (tableName, partitionKey, sortKey, region = 'us-east-1') => {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const currentTime = Math.floor(Date.now() / 1000);
    const expireAt = Math.floor((Date.now() + 90 * 24 * 60 * 60 * 1000) / 1000);

    const params = {
        TableName: tableName,
        Key: marshall({
            partitionKey: partitionKey,
            sortKey: sortKey
        }),
        UpdateExpression: "SET updatedAt = :c, expireAt = :e",
        ExpressionAttributeValues: marshall({
            ":c": currentTime,
            ":e": expireAt
        }),
    };

    try {
        const data = await client.send(new UpdateItemCommand(params));
        const responseData = unmarshall(data.Attributes);
        console.log("Item updated successfully: %s", responseData);
        return responseData;
    } catch (err) {
        console.error("Error updating item:", err);
        throw err;
    }
}

// Example usage (commented out for testing)
// updateItem('your-table-name', 'your-partition-key-value', 'your-sort-key-value');
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 使用 PartiQL UPDATE 更新数据
<a name="dynamodb_PartiQLUpdate_javascript_3_topic"></a>

以下代码示例演示如何使用 PartiQL UPDATE 语句更新数据。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用带有的 PartiQL UPDATE 语句更新 DynamoDB 表中的项目。 适用于 JavaScript 的 AWS SDK  

```
/**
 * This example demonstrates how to update items in a DynamoDB table using PartiQL.
 * It shows different ways to update documents with various index types.
 */
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  ExecuteStatementCommand,
  BatchExecuteStatementCommand,
} from "@aws-sdk/lib-dynamodb";

/**
 * Update a single attribute of an item using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param attributeName - The name of the attribute to update
 * @param attributeValue - The new value for the attribute
 * @returns The response from the ExecuteStatementCommand
 */
export const updateSingleAttribute = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  attributeName: string,
  attributeValue: any
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `UPDATE "${tableName}" SET ${attributeName} = ? WHERE ${partitionKeyName} = ?`,
    Parameters: [attributeValue, partitionKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item updated successfully");
    return data;
  } catch (err) {
    console.error("Error updating item:", err);
    throw err;
  }
};

/**
 * Update multiple attributes of an item using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param attributeUpdates - Object containing attribute names and their new values
 * @returns The response from the ExecuteStatementCommand
 */
export const updateMultipleAttributes = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  attributeUpdates: Record<string, any>
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  // Create SET clause for each attribute
  const setClause = Object.keys(attributeUpdates)
    .map((attr, index) => `${attr} = ?`)
    .join(", ");

  // Create parameters array with attribute values followed by the partition key value
  const parameters = [...Object.values(attributeUpdates), partitionKeyValue];

  const params = {
    Statement: `UPDATE "${tableName}" SET ${setClause} WHERE ${partitionKeyName} = ?`,
    Parameters: parameters,
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item updated successfully");
    return data;
  } catch (err) {
    console.error("Error updating item:", err);
    throw err;
  }
};

/**
 * Update an item identified by a composite key (partition key + sort key) using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param sortKeyName - The name of the sort key attribute
 * @param sortKeyValue - The value of the sort key
 * @param attributeName - The name of the attribute to update
 * @param attributeValue - The new value for the attribute
 * @returns The response from the ExecuteStatementCommand
 */
export const updateItemWithCompositeKey = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  sortKeyName: string,
  sortKeyValue: string | number,
  attributeName: string,
  attributeValue: any
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `UPDATE "${tableName}" SET ${attributeName} = ? WHERE ${partitionKeyName} = ? AND ${sortKeyName} = ?`,
    Parameters: [attributeValue, partitionKeyValue, sortKeyValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item updated successfully");
    return data;
  } catch (err) {
    console.error("Error updating item:", err);
    throw err;
  }
};

/**
 * Update an item with a condition to ensure the update only happens if a condition is met.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param partitionKeyName - The name of the partition key attribute
 * @param partitionKeyValue - The value of the partition key
 * @param attributeName - The name of the attribute to update
 * @param attributeValue - The new value for the attribute
 * @param conditionAttribute - The attribute to check in the condition
 * @param conditionValue - The value to compare against in the condition
 * @returns The response from the ExecuteStatementCommand
 */
export const updateItemWithCondition = async (
  tableName: string,
  partitionKeyName: string,
  partitionKeyValue: string | number,
  attributeName: string,
  attributeValue: any,
  conditionAttribute: string,
  conditionValue: any
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  const params = {
    Statement: `UPDATE "${tableName}" SET ${attributeName} = ? WHERE ${partitionKeyName} = ? AND ${conditionAttribute} = ?`,
    Parameters: [attributeValue, partitionKeyValue, conditionValue],
  };

  try {
    const data = await docClient.send(new ExecuteStatementCommand(params));
    console.log("Item updated with condition successfully");
    return data;
  } catch (err) {
    console.error("Error updating item with condition:", err);
    throw err;
  }
};

/**
 * Batch update multiple items using PartiQL.
 * 
 * @param tableName - The name of the DynamoDB table
 * @param updates - Array of objects containing key and update information
 * @returns The response from the BatchExecuteStatementCommand
 */
export const batchUpdateItems = async (
  tableName: string,
  updates: Array<{
    partitionKeyName: string;
    partitionKeyValue: string | number;
    attributeName: string;
    attributeValue: any;
  }>
) => {
  const client = new DynamoDBClient({});
  const docClient = DynamoDBDocumentClient.from(client);

  // Create statements for each update
  const statements = updates.map((update) => {
    return {
      Statement: `UPDATE "${tableName}" SET ${update.attributeName} = ? WHERE ${update.partitionKeyName} = ?`,
      Parameters: [update.attributeValue, update.partitionKeyValue],
    };
  });

  const params = {
    Statements: statements,
  };

  try {
    const data = await docClient.send(new BatchExecuteStatementCommand(params));
    console.log("Items batch updated successfully");
    return data;
  } catch (err) {
    console.error("Error batch updating items:", err);
    throw err;
  }
};

/**
 * Example usage showing how to update items with different index types
 */
export const updateExamples = async () => {
  // Update a single attribute using a simple primary key
  await updateSingleAttribute("UsersTable", "userId", "user123", "email", "newemail@example.com");

  // Update multiple attributes at once
  await updateMultipleAttributes("UsersTable", "userId", "user123", {
    email: "newemail@example.com",
    name: "John Smith",
    lastLogin: new Date().toISOString(),
  });

  // Update an item with a composite key (partition key + sort key)
  await updateItemWithCompositeKey(
    "OrdersTable",
    "orderId",
    "order456",
    "productId",
    "prod789",
    "quantity",
    5
  );

  // Update with a condition
  await updateItemWithCondition(
    "UsersTable",
    "userId",
    "user123",
    "userStatus",
    "active",
    "userType",
    "premium"
  );

  // Batch update multiple items
  await batchUpdateItems("UsersTable", [
    {
      partitionKeyName: "userId",
      partitionKeyValue: "user123",
      attributeName: "lastLogin",
      attributeValue: new Date().toISOString(),
    },
    {
      partitionKeyName: "userId",
      partitionKeyValue: "user456",
      attributeName: "lastLogin",
      attributeValue: new Date().toISOString(),
    },
  ]);
};
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [BatchExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/BatchExecuteStatementCommand)
  + [ExecuteStatement](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/ExecuteStatementCommand)

### 使用 API Gateway 调用 Lambda 函数
<a name="cross_LambdaAPIGateway_javascript_3_topic"></a>

以下代码示例展示了如何创建由 Amazon API Gateway 调用的 AWS Lambda 函数。

**适用于 JavaScript (v3) 的软件开发工具包**  
 演示如何使用 Lambda JavaScript 运行时 API 创建 AWS Lambda 函数。此示例调用不同的 AWS 服务来执行特定的用例。此示例展示了如何创建通过 Amazon API Gateway 调用的 Lambda 函数，该函数扫描 Amazon DynamoDB 表获取工作周年纪念日，并使用 Amazon Simple Notification Service (Amazon SNS)向员工发送文本消息，祝贺他们的周年纪念日。  
 有关如何设置和运行的完整源代码和说明，请参阅上的完整示例[GitHub](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/lambda-api-gateway)。  
该示例也可在 [适用于 JavaScript 的 AWS SDK v3 开发人员指南](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/api-gateway-invoking-lambda-example.html)中找到。  

**本示例中使用的服务**
+ API Gateway
+ DynamoDB
+ Lambda
+ Amazon SNS

### 使用原子计数器操作
<a name="dynamodb_Scenario_AtomicCounterOperations_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中使用原子计数器操作。
+ 使用 ADD 和 SET 操作以原子方式递增计数器。
+ 安全地递增可能不存在的计数器。
+ 为计数器操作实施乐观锁。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示原子计数器操作 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Increment a counter using the ADD operation.
 * 
 * This function demonstrates using the ADD operation for atomic increments.
 * The ADD operation is atomic and is the recommended way to increment counters.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} counterName - The name of the counter attribute
 * @param {number} incrementValue - The value to increment by
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function incrementCounterWithAdd(
  config,
  tableName,
  key,
  counterName,
  incrementValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using ADD
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `ADD ${counterName} :increment`,
    ExpressionAttributeValues: {
      ":increment": incrementValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Increment a counter using the SET operation with an expression.
 * 
 * This function demonstrates using the SET operation with an expression for increments.
 * While this approach works, it's less idiomatic for simple increments than using ADD.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} counterName - The name of the counter attribute
 * @param {number} incrementValue - The value to increment by
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function incrementCounterWithSet(
  config,
  tableName,
  key,
  counterName,
  incrementValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using SET with an expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${counterName} = ${counterName} + :increment`,
    ExpressionAttributeValues: {
      ":increment": incrementValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Increment a counter safely, handling the case where the counter might not exist.
 * 
 * This function demonstrates using the if_not_exists function with SET to safely
 * increment a counter that might not exist yet.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} counterName - The name of the counter attribute
 * @param {number} incrementValue - The value to increment by
 * @param {number} defaultValue - The default value if the counter doesn't exist
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function incrementCounterSafely(
  config,
  tableName,
  key,
  counterName,
  incrementValue,
  defaultValue = 0
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using SET with if_not_exists
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${counterName} = if_not_exists(${counterName}, :default) + :increment`,
    ExpressionAttributeValues: {
      ":increment": incrementValue,
      ":default": defaultValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Increment a counter with optimistic locking to prevent race conditions.
 * 
 * This function demonstrates using a condition expression to implement optimistic
 * locking, which prevents race conditions when multiple processes try to update
 * the same counter.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} counterName - The name of the counter attribute
 * @param {number} incrementValue - The value to increment by
 * @param {number} expectedValue - The expected current value of the counter
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function incrementCounterWithLocking(
  config,
  tableName,
  key,
  counterName,
  incrementValue,
  expectedValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${counterName} = ${counterName} + :increment`,
    ConditionExpression: `${counterName} = :expected`,
    ExpressionAttributeValues: {
      ":increment": incrementValue,
      ":expected": expectedValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    return {
      success: true,
      data: response
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        error: "Optimistic locking failed: the counter value has changed"
      };
    }
    // Re-throw other errors
    throw error;
  }
}

/**
 * Get the current value of a counter.
 * 
 * Helper function to retrieve the current value of a counter attribute.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @param {string} counterName - The name of the counter attribute
 * @returns {Promise<number|null>} - The current counter value or null if not found
 */
async function getCounterValue(
  config,
  tableName,
  key,
  counterName
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the counter value if it exists, otherwise null
  return response.Item && counterName in response.Item
    ? response.Item[counterName]
    : null;
}
```
使用原子计数器操作的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to use the atomic counter operations.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const key = { ProductId: "P12345" };
  const counterName = "ViewCount";
  const incrementValue = 1;
  
  console.log("Demonstrating different approaches to increment counters in DynamoDB");
  
  try {
    // Example 1: Using ADD operation (recommended for simple increments)
    console.log("\nExample 1: Incrementing counter with ADD operation");
    const response1 = await incrementCounterWithAdd(
      config,
      tableName,
      key,
      counterName,
      incrementValue
    );
    
    console.log(`Counter incremented to: ${response1.Attributes[counterName]}`);
    
    // Example 2: Using SET operation with an expression
    console.log("\nExample 2: Incrementing counter with SET operation");
    const response2 = await incrementCounterWithSet(
      config,
      tableName,
      key,
      counterName,
      incrementValue
    );
    
    console.log(`Counter incremented to: ${response2.Attributes[counterName]}`);
    
    // Example 3: Safely incrementing a counter that might not exist
    console.log("\nExample 3: Safely incrementing counter that might not exist");
    const newKey = { ProductId: "P67890" };
    const response3 = await incrementCounterSafely(
      config,
      tableName,
      newKey,
      counterName,
      incrementValue,
      0
    );
    
    console.log(`Counter initialized and incremented to: ${response3.Attributes[counterName]}`);
    
    // Example 4: Incrementing with optimistic locking
    console.log("\nExample 4: Incrementing with optimistic locking");
    
    // First, get the current counter value
    const currentValue = await getCounterValue(config, tableName, key, counterName);
    console.log(`Current counter value: ${currentValue}`);
    
    // Then, try to increment with optimistic locking
    const response4 = await incrementCounterWithLocking(
      config,
      tableName,
      key,
      counterName,
      incrementValue,
      currentValue
    );
    
    if (response4.success) {
      console.log(`Counter successfully incremented to: ${response4.data.Attributes[counterName]}`);
    } else {
      console.log(response4.error);
    }
    
    // Explain the differences between ADD and SET
    console.log("\nKey differences between ADD and SET for counter operations:");
    console.log("1. ADD is more concise and idiomatic for simple increments");
    console.log("2. SET with expressions is more flexible for complex operations");
    console.log("3. Both operations are atomic and safe for concurrent updates");
    console.log("4. SET with if_not_exists is required when the attribute might not exist");
    console.log("5. Optimistic locking can be added to either approach for additional safety");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+  有关 API 的详细信息，请参阅 *适用于 JavaScript 的 AWS SDK API 参考[UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)*中的。

### 使用条件运算
<a name="dynamodb_Scenario_ConditionalOperations_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中使用条件运算。
+ 实现条件写入以防止覆盖数据。
+ 使用条件表达式以强制实施业务规则。
+ 从容处理条件检查失败。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示条件运算 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  DeleteCommand,
  GetCommand,
  PutCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Perform a conditional update operation.
 * 
 * This function demonstrates how to update an item only if a condition is met.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} conditionAttribute - The attribute to check in the condition
 * @param {any} conditionValue - The value to compare against
 * @param {string} updateAttribute - The attribute to update
 * @param {any} updateValue - The new value to set
 * @returns {Promise<Object>} - Result of the operation
 */
async function conditionalUpdate(
  config,
  tableName,
  key,
  conditionAttribute,
  conditionValue,
  updateAttribute,
  updateValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${updateAttribute} = :value`,
    ConditionExpression: `${conditionAttribute} = :condition`,
    ExpressionAttributeValues: {
      ":value": updateValue,
      ":condition": conditionValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    
    return {
      success: true,
      message: "Condition was met and update was performed",
      updatedAttributes: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Condition was not met, update was not performed",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Perform a conditional delete operation.
 * 
 * This function demonstrates how to delete an item only if a condition is met.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to delete
 * @param {string} conditionAttribute - The attribute to check in the condition
 * @param {any} conditionValue - The value to compare against
 * @returns {Promise<Object>} - Result of the operation
 */
async function conditionalDelete(
  config,
  tableName,
  key,
  conditionAttribute,
  conditionValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the delete parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    ConditionExpression: `${conditionAttribute} = :condition`,
    ExpressionAttributeValues: {
      ":condition": conditionValue
    },
    ReturnValues: "ALL_OLD"
  };
  
  try {
    // Perform the delete operation
    const response = await docClient.send(new DeleteCommand(params));
    
    return {
      success: true,
      message: "Condition was met and item was deleted",
      deletedItem: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Condition was not met, item was not deleted",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Implement optimistic locking with a version number.
 * 
 * This function demonstrates how to use a version number for optimistic locking
 * to prevent race conditions when multiple processes update the same item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {Object} updates - The attributes to update
 * @param {number} expectedVersion - The expected current version number
 * @returns {Promise<Object>} - Result of the operation
 */
async function updateWithOptimisticLocking(
  config,
  tableName,
  key,
  updates,
  expectedVersion
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression
  const updateExpressions = [];
  const expressionAttributeValues = {
    ":expectedVersion": expectedVersion,
    ":newVersion": expectedVersion + 1
  };
  
  // Add each update to the expression
  Object.entries(updates).forEach(([attribute, value], index) => {
    updateExpressions.push(`${attribute} = :val${index}`);
    expressionAttributeValues[`:val${index}`] = value;
  });
  
  // Add the version update
  updateExpressions.push("version = :newVersion");
  
  // Define the update parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${updateExpressions.join(", ")}`,
    ConditionExpression: "version = :expectedVersion",
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    
    return {
      success: true,
      message: "Update succeeded with optimistic locking",
      newVersion: expectedVersion + 1,
      updatedAttributes: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Optimistic locking failed: the item was modified by another process",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Implement a conditional write that creates an item only if it doesn't exist.
 * 
 * This function demonstrates how to use attribute_not_exists to create an item
 * only if it doesn't already exist (similar to an "INSERT IF NOT EXISTS" operation).
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} item - The item to create
 * @returns {Promise<Object>} - Result of the operation
 */
async function createIfNotExists(
  config,
  tableName,
  item
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Extract the primary key attributes
  const keyAttributes = Object.keys(item).filter(attr => 
    attr === "id" || attr === "ID" || attr === "Id" || 
    attr.endsWith("Id") || attr.endsWith("ID") || 
    attr.endsWith("Key")
  );
  
  if (keyAttributes.length === 0) {
    throw new Error("Could not determine primary key attributes");
  }
  
  // Create a condition expression that checks if the item doesn't exist
  const conditionExpression = `attribute_not_exists(${keyAttributes[0]})`;
  
  // Define the put parameters with a condition expression
  const params = {
    TableName: tableName,
    Item: item,
    ConditionExpression: conditionExpression
  };
  
  try {
    // Perform the put operation
    await docClient.send(new PutCommand(params));
    
    return {
      success: true,
      message: "Item was created because it didn't exist",
      item
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Item already exists, creation was skipped",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}
```
条件运算的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to use conditional operations.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const key = { ProductId: "P12345" };
  
  console.log("Demonstrating conditional operations in DynamoDB");
  
  try {
    // Example 1: Conditional update based on attribute value
    console.log("\nExample 1: Conditional update based on attribute value");
    const updateResult = await conditionalUpdate(
      config,
      tableName,
      key,
      "Category",
      "Electronics",
      "Price",
      299.99
    );
    
    console.log(`Result: ${updateResult.message}`);
    if (updateResult.success) {
      console.log("Updated attributes:", updateResult.updatedAttributes);
    }
    
    // Example 2: Conditional delete based on attribute value
    console.log("\nExample 2: Conditional delete based on attribute value");
    const deleteResult = await conditionalDelete(
      config,
      tableName,
      key,
      "InStock",
      false
    );
    
    console.log(`Result: ${deleteResult.message}`);
    if (deleteResult.success) {
      console.log("Deleted item:", deleteResult.deletedItem);
    }
    
    // Example 3: Optimistic locking with version number
    console.log("\nExample 3: Optimistic locking with version number");
    
    // First, get the current item to check its version
    const currentItem = await getItem(config, tableName, { ProductId: "P67890" });
    const currentVersion = currentItem ? (currentItem.version || 0) : 0;
    
    console.log(`Current version: ${currentVersion}`);
    
    // Then, update with optimistic locking
    const lockingResult = await updateWithOptimisticLocking(
      config,
      tableName,
      { ProductId: "P67890" },
      {
        Name: "Updated Product Name",
        Description: "This is an updated description"
      },
      currentVersion
    );
    
    console.log(`Result: ${lockingResult.message}`);
    if (lockingResult.success) {
      console.log(`New version: ${lockingResult.newVersion}`);
      console.log("Updated attributes:", lockingResult.updatedAttributes);
    }
    
    // Example 4: Create item only if it doesn't exist
    console.log("\nExample 4: Create item only if it doesn't exist");
    const createResult = await createIfNotExists(
      config,
      tableName,
      {
        ProductId: "P99999",
        Name: "New Product",
        Category: "Accessories",
        Price: 19.99,
        InStock: true
      }
    );
    
    console.log(`Result: ${createResult.message}`);
    if (createResult.success) {
      console.log("Created item:", createResult.item);
    }
    
    // Explain conditional operations
    console.log("\nKey points about conditional operations:");
    console.log("1. Conditional operations only succeed if the condition is met");
    console.log("2. ConditionalCheckFailedException indicates the condition wasn't met");
    console.log("3. Optimistic locking prevents race conditions in concurrent updates");
    console.log("4. attribute_exists and attribute_not_exists are useful for checking if attributes are present");
    console.log("5. Conditional operations are atomic - they either succeed completely or fail completely");
    console.log("6. You can use any valid comparison operators and functions in condition expressions");
    console.log("7. Conditional operations don't consume write capacity if the condition fails");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [DeleteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteItemCommand)
  + [PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)
  + [UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)

### 使用表达式属性名称
<a name="dynamodb_Scenario_ExpressionAttributeNames_javascript_3_topic"></a>

以下代码示例演示如何在 DynamoDB 中使用表达式属性名称。
+ 在 DynamoDB 表达式中使用保留字。
+ 使用表达式属性名称占位符。
+ 处理属性名称中的特殊字符。

**适用于 JavaScript (v3) 的软件开发工具包**  
使用演示表达式属性名称 适用于 JavaScript 的 AWS SDK。  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand,
  QueryCommand,
  ScanCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Update an attribute that is a reserved word in DynamoDB.
 * 
 * This function demonstrates how to use expression attribute names to update
 * attributes that are reserved words in DynamoDB.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} reservedWordAttribute - The reserved word attribute to update
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateReservedWordAttribute(
  config,
  tableName,
  key,
  reservedWordAttribute,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using expression attribute names
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: "SET #attr = :value",
    ExpressionAttributeNames: {
      "#attr": reservedWordAttribute
    },
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Update an attribute that contains special characters.
 * 
 * This function demonstrates how to use expression attribute names to update
 * attributes that contain special characters.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} specialCharAttribute - The attribute with special characters to update
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateSpecialCharacterAttribute(
  config,
  tableName,
  key,
  specialCharAttribute,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters using expression attribute names
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: "SET #attr = :value",
    ExpressionAttributeNames: {
      "#attr": specialCharAttribute
    },
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Query items using an attribute that is a reserved word.
 * 
 * This function demonstrates how to use expression attribute names in a query
 * when the attribute is a reserved word.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {string} partitionKeyName - The name of the partition key attribute
 * @param {any} partitionKeyValue - The value of the partition key
 * @param {string} reservedWordAttribute - The reserved word attribute to filter on
 * @param {any} value - The value to compare against
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function queryWithReservedWordAttribute(
  config,
  tableName,
  partitionKeyName,
  partitionKeyValue,
  reservedWordAttribute,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the query parameters using expression attribute names
  const params = {
    TableName: tableName,
    KeyConditionExpression: "#pkName = :pkValue",
    FilterExpression: "#attr = :value",
    ExpressionAttributeNames: {
      "#pkName": partitionKeyName,
      "#attr": reservedWordAttribute
    },
    ExpressionAttributeValues: {
      ":pkValue": partitionKeyValue,
      ":value": value
    }
  };
  
  // Perform the query operation
  const response = await docClient.send(new QueryCommand(params));
  
  return response;
}

/**
 * Update a nested attribute with a path that contains reserved words.
 * 
 * This function demonstrates how to use expression attribute names to update
 * nested attributes where the path contains reserved words.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string[]} attributePath - The path to the nested attribute as an array
 * @param {any} value - The value to set
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateNestedReservedWordAttribute(
  config,
  tableName,
  key,
  attributePath,
  value
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create expression attribute names for each part of the path
  const expressionAttributeNames = {};
  for (let i = 0; i < attributePath.length; i++) {
    expressionAttributeNames[`#attr${i}`] = attributePath[i];
  }
  
  // Build the attribute path using the expression attribute names
  const attributePathExpression = attributePath
    .map((_, i) => `#attr${i}`)
    .join(".");
  
  // Define the update parameters
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${attributePathExpression} = :value`,
    ExpressionAttributeNames: expressionAttributeNames,
    ExpressionAttributeValues: {
      ":value": value
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  // Perform the update operation
  const response = await docClient.send(new UpdateCommand(params));
  
  return response;
}

/**
 * Scan a table with multiple attribute name placeholders.
 * 
 * This function demonstrates how to use multiple expression attribute names
 * in a complex filter expression.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} filters - Object mapping attribute names to filter values
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function scanWithMultipleAttributeNames(
  config,
  tableName,
  filters
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Create expression attribute names and values
  const expressionAttributeNames = {};
  const expressionAttributeValues = {};
  const filterConditions = [];
  
  // Build the filter expression
  Object.entries(filters).forEach(([attrName, value], index) => {
    const nameKey = `#attr${index}`;
    const valueKey = `:val${index}`;
    
    expressionAttributeNames[nameKey] = attrName;
    expressionAttributeValues[valueKey] = value;
    filterConditions.push(`${nameKey} = ${valueKey}`);
  });
  
  // Join the filter conditions with AND
  const filterExpression = filterConditions.join(" AND ");
  
  // Define the scan parameters
  const params = {
    TableName: tableName,
    FilterExpression: filterExpression,
    ExpressionAttributeNames: expressionAttributeNames,
    ExpressionAttributeValues: expressionAttributeValues
  };
  
  // Perform the scan operation
  const response = await docClient.send(new ScanCommand(params));
  
  return response;
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}
```
表达式属性名称的用法示例 适用于 JavaScript 的 AWS SDK。  

```
/**
 * Example of how to use expression attribute names.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const key = { ProductId: "P12345" };
  
  console.log("Demonstrating expression attribute names in DynamoDB");
  
  try {
    // Example 1: Update an attribute that is a reserved word
    console.log("\nExample 1: Updating an attribute that is a reserved word");
    const response1 = await updateReservedWordAttribute(
      config,
      tableName,
      key,
      "Size", // "SIZE" is a reserved word in DynamoDB
      "Large"
    );
    
    console.log("Updated attribute:", response1.Attributes);
    
    // Example 2: Update an attribute with special characters
    console.log("\nExample 2: Updating an attribute with special characters");
    const response2 = await updateSpecialCharacterAttribute(
      config,
      tableName,
      key,
      "Product-Type", // Contains a hyphen, which is a special character
      "Electronics"
    );
    
    console.log("Updated attribute:", response2.Attributes);
    
    // Example 3: Query with a reserved word attribute
    console.log("\nExample 3: Querying with a reserved word attribute");
    const response3 = await queryWithReservedWordAttribute(
      config,
      tableName,
      "Category",
      "Electronics",
      "Count", // "COUNT" is a reserved word in DynamoDB
      10
    );
    
    console.log(`Found ${response3.Items.length} items`);
    
    // Example 4: Update a nested attribute with reserved words in the path
    console.log("\nExample 4: Updating a nested attribute with reserved words in the path");
    const response4 = await updateNestedReservedWordAttribute(
      config,
      tableName,
      key,
      ["Dimensions", "Size", "Height"], // "SIZE" is a reserved word
      30
    );
    
    console.log("Updated nested attribute:", response4.Attributes);
    
    // Example 5: Scan with multiple attribute name placeholders
    console.log("\nExample 5: Scanning with multiple attribute name placeholders");
    const response5 = await scanWithMultipleAttributeNames(
      config,
      tableName,
      {
        "Size": "Large",
        "Count": 10,
        "Product-Type": "Electronics"
      }
    );
    
    console.log(`Found ${response5.Items.length} items`);
    
    // Get the final state of the item
    console.log("\nFinal state of the item:");
    const item = await getItem(config, tableName, key);
    console.log(JSON.stringify(item, null, 2));
    
    // Show some common reserved words
    console.log("\nSome common DynamoDB reserved words:");
    const commonReservedWords = [
      "ABORT", "ABSOLUTE", "ACTION", "ADD", "ALL", "ALTER", "AND", "ANY", "AS",
      "ASC", "BETWEEN", "BY", "CASE", "CAST", "COLUMN", "CONNECT", "COUNT",
      "CREATE", "CURRENT", "DATE", "DELETE", "DESC", "DROP", "ELSE", "EXISTS",
      "FOR", "FROM", "GRANT", "GROUP", "HAVING", "IN", "INDEX", "INSERT", "INTO",
      "IS", "JOIN", "KEY", "LEVEL", "LIKE", "LIMIT", "LOCAL", "MAX", "MIN", "NAME",
      "NOT", "NULL", "OF", "ON", "OR", "ORDER", "OUTER", "REPLACE", "RETURN",
      "SELECT", "SET", "SIZE", "TABLE", "THEN", "TO", "UPDATE", "USER", "VALUES",
      "VIEW", "WHERE"
    ];
    console.log(commonReservedWords.join(", "));
    
    // Explain expression attribute names
    console.log("\nKey points about expression attribute names:");
    console.log("1. Use expression attribute names (#name) for reserved words");
    console.log("2. Use expression attribute names for attributes with special characters");
    console.log("3. Special characters include: spaces, hyphens, dots, and other non-alphanumeric characters");
    console.log("4. Expression attribute names are required for nested attributes with reserved words");
    console.log("5. You can use multiple expression attribute names in a single expression");
    console.log("6. Expression attribute names are case-sensitive");
    console.log("7. Expression attribute names are only used in expressions, not in the actual data");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+ 有关 API 详细信息，请参阅《适用于 JavaScript 的 AWS SDK API Reference》**中的以下主题。
  + [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)
  + [UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)

### 使用计划的事件调用 Lambda 函数
<a name="cross_LambdaScheduledEvents_javascript_3_topic"></a>

以下代码示例显示如何创建由 Amazon EventBridge 计划事件调用的 AWS Lambda 函数。

**适用于 JavaScript (v3) 的软件开发工具包**  
 演示如何创建调用函数的 Amazon EventBridge 计划事件。 AWS Lambda 配置 EventBridge 为使用 cron 表达式来调度 Lambda 函数的调用时间。在此示例中，您将使用 Lambda 运行时 API 创建一个 Lambda 函数。 JavaScript 此示例调用不同的 AWS 服务来执行特定的用例。此示例展示了如何创建一个应用程序，在其一周年纪念日时向员工发送移动短信表示祝贺。  
 有关如何设置和运行的完整源代码和说明，请参阅上的完整示例[GitHub](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/lambda-scheduled-events)。  
该示例也可在 [适用于 JavaScript 的 AWS SDK v3 开发人员指南](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/scheduled-events-invoking-lambda-example.html)中找到。  

**本示例中使用的服务**
+ CloudWatch 日志
+ DynamoDB
+ EventBridge
+ Lambda
+ Amazon SNS

## 无服务器示例
<a name="serverless_examples"></a>

### 通过 DynamoDB 触发器调用 Lambda 函数
<a name="serverless_DynamoDB_Lambda_javascript_3_topic"></a>

以下代码示例演示如何实现一个 Lambda 函数，该函数接收通过接收来自 DynamoDB 流的记录而触发的事件。该函数检索 DynamoDB 有效负载，并记录下记录内容。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在[无服务器示例](https://github.com/aws-samples/serverless-snippets/tree/main/integration-ddb-to-lambda)存储库中查找完整示例，并了解如何进行设置和运行。
使用 Lambda 使用一个 DynamoDB 事件。 JavaScript  

```
// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
exports.handler = async (event, context) => {
    console.log(JSON.stringify(event, null, 2));
    event.Records.forEach(record => {
        logDynamoDBRecord(record);
    });
};

const logDynamoDBRecord = (record) => {
    console.log(record.eventID);
    console.log(record.eventName);
    console.log(`DynamoDB Record: ${JSON.stringify(record.dynamodb)}`);
};
```
使用 Lambda 使用一个 DynamoDB 事件。 TypeScript  

```
export const handler = async (event, context) => {
    console.log(JSON.stringify(event, null, 2));
    event.Records.forEach(record => {
        logDynamoDBRecord(record);
    });
}
const logDynamoDBRecord = (record) => {
    console.log(record.eventID);
    console.log(record.eventName);
    console.log(`DynamoDB Record: ${JSON.stringify(record.dynamodb)}`);
};
```

### 通过 DynamoDB 触发器报告 Lambda 函数批处理项目失败
<a name="serverless_DynamoDB_Lambda_batch_item_failures_javascript_3_topic"></a>

以下代码示例演示如何为接收来自 DynamoDB 流的事件的 Lambda 函数实现部分批处理响应。该函数在响应中报告批处理项目失败，并指示 Lambda 稍后重试这些消息。

**适用于 JavaScript (v3) 的软件开发工具包**  
 还有更多相关信息 GitHub。在[无服务器示例](https://github.com/aws-samples/serverless-snippets/tree/main/integration-ddb-to-lambda-with-batch-item-handling)存储库中查找完整示例，并了解如何进行设置和运行。
使用 Lambda 报告 DynamoDB 批处理项目失败。 JavaScript  

```
export const handler = async (event) => {
  const records = event.Records;
  let curRecordSequenceNumber = "";

  for (const record of records) {
    try {
      // Process your record
      curRecordSequenceNumber = record.dynamodb.SequenceNumber;
    } catch (e) {
      // Return failed record's sequence number
      return { batchItemFailures: [{ itemIdentifier: curRecordSequenceNumber }] };
    }
  }

  return { batchItemFailures: [] };
};
```
使用 Lambda 报告 DynamoDB 批处理项目失败。 TypeScript  

```
import {
  DynamoDBBatchResponse,
  DynamoDBBatchItemFailure,
  DynamoDBStreamEvent,
} from "aws-lambda";

export const handler = async (
  event: DynamoDBStreamEvent
): Promise<DynamoDBBatchResponse> => {
  const batchItemFailures: DynamoDBBatchItemFailure[] = [];
  let curRecordSequenceNumber;

  for (const record of event.Records) {
    curRecordSequenceNumber = record.dynamodb?.SequenceNumber;

    if (curRecordSequenceNumber) {
      batchItemFailures.push({
        itemIdentifier: curRecordSequenceNumber,
      });
    }
  }

  return { batchItemFailures: batchItemFailures };
};
```