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# 使用 DynamoDB 中的表
<a name="examples-dynamodb-tables"></a>

表是 DynamoDB 数据库中所有项目的容器。您必须先创建表，然后才能在 DynamoDB 中添加或删除数据。

对于每个表，您必须定义：
+ 对你 AWS 账户 和来说是唯一的表*名* AWS 区域。
+ 一个主键**，其每个值都必须是唯一的。表中的任何两个项目都不能具有相同的主键值。

  主键可以是*简单*主键（包含单个分区 (HASH) 键）或*复合*主键（包含一个分区和一个排序 (RANGE) 键）。

  每个键值均有一个由 [ScalarAttributeType](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/namespace_aws_1_1_dynamo_d_b_1_1_model.html#a4b39ae66214e022d3737079d071e4bcb.html) 类枚举的关联*数据类型*。键值可以是二进制 (B)、数字 (N) 或字符串 (S)。有关更多信息，请参阅《Amazon DynamoDB 开发人员指南》中的[命名规则和数据类型](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html)。
+  *预置吞吐量*值，用于定义表的预留 read/write 容量单位数。
**注意**  
 [Amazon DynamoDB 定价](https://aws.amazon.com/dynamodb/pricing/)基于您为表设置的预置吞吐量值，因此您应只为表保留可能需要的容量。  
表的预置吞吐量可随时修改，以便您能够在需要更改时调整容量。

## 创建表
<a name="dynamodb-create-table"></a>

使用 [DynamoDB 客户端](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)的 `CreateTable` 方法可创建新的 DynamoDB 表。您需要构造表属性和表架构，二者用于标识表的主键。您还必须提供初始预置吞吐量值和表名。`CreateTable` 是一个异步操作。`GetTableStatus` 在表格处于活动状态并可供使用之前，将返回 CREATING。

### 创建具有简单主键的表
<a name="dynamodb-create-table-simple"></a>

此代码使用简单主键（“Name”）创建表。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/AttributeDefinition.h>
#include <aws/dynamodb/model/CreateTableRequest.h>
#include <aws/dynamodb/model/KeySchemaElement.h>
#include <aws/dynamodb/model/ProvisionedThroughput.h>
#include <aws/dynamodb/model/ScalarAttributeType.h>
#include <iostream>
```

 **代码** 

```
//! Create an Amazon DynamoDB table.
/*!
  \sa createTable()
  \param tableName: Name for the DynamoDB table.
  \param primaryKey: Primary key for the DynamoDB table.
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
 */
bool AwsDoc::DynamoDB::createTable(const Aws::String &tableName,
                                   const Aws::String &primaryKey,
                                   const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    std::cout << "Creating table " << tableName <<
              " with a simple primary key: \"" << primaryKey << "\"." << std::endl;

    Aws::DynamoDB::Model::CreateTableRequest request;

    Aws::DynamoDB::Model::AttributeDefinition hashKey;
    hashKey.SetAttributeName(primaryKey);
    hashKey.SetAttributeType(Aws::DynamoDB::Model::ScalarAttributeType::S);
    request.AddAttributeDefinitions(hashKey);

    Aws::DynamoDB::Model::KeySchemaElement keySchemaElement;
    keySchemaElement.WithAttributeName(primaryKey).WithKeyType(
            Aws::DynamoDB::Model::KeyType::HASH);
    request.AddKeySchema(keySchemaElement);

    Aws::DynamoDB::Model::ProvisionedThroughput throughput;
    throughput.WithReadCapacityUnits(5).WithWriteCapacityUnits(5);
    request.SetProvisionedThroughput(throughput);
    request.SetTableName(tableName);

    const Aws::DynamoDB::Model::CreateTableOutcome &outcome = dynamoClient.CreateTable(
            request);
    if (outcome.IsSuccess()) {
        std::cout << "Table \""
                  << outcome.GetResult().GetTableDescription().GetTableName() <<
                  " created!" << std::endl;
    }
    else {
        std::cerr << "Failed to create table: " << outcome.GetError().GetMessage()
                  << std::endl;
        return false;
    }

    return waitTableActive(tableName, dynamoClient);
}
```

请参阅[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/create_table.cpp)。

### 创建具有复合主键的表
<a name="dynamodb-create-table-composite"></a>

将另一个[AttributeDefinition](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_model_1_1_attribute_definition.html)和添加[KeySchemaElement](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_model_1_1_key_schema_element.html)到[CreateTableRequest](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_model_1_1_create_table_request.html)。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/AttributeDefinition.h>
#include <aws/dynamodb/model/CreateTableRequest.h>
#include <aws/dynamodb/model/KeySchemaElement.h>
#include <aws/dynamodb/model/ProvisionedThroughput.h>
#include <aws/dynamodb/model/ScalarAttributeType.h>
#include <iostream>
```

 **代码** 

```
//! Create an Amazon DynamoDB table with a composite key.
/*!
  \sa createTableWithCompositeKey()
  \param tableName: Name for the DynamoDB table.
  \param partitionKey: Name for the partition (hash) key.
  \param sortKey: Name for the sort (range) key.
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
 */
bool AwsDoc::DynamoDB::createTableWithCompositeKey(const Aws::String &tableName,
                                                   const Aws::String &partitionKey,
                                                   const Aws::String &sortKey,
                                                   const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    std::cout << "Creating table " << tableName <<
              " with a composite primary key:\n" \
            "* " << partitionKey << " - partition key\n" \
            "* " << sortKey << " - sort key\n";

    Aws::DynamoDB::Model::CreateTableRequest request;

    Aws::DynamoDB::Model::AttributeDefinition hashKey1, hashKey2;
    hashKey1.WithAttributeName(partitionKey).WithAttributeType(
            Aws::DynamoDB::Model::ScalarAttributeType::S);
    request.AddAttributeDefinitions(hashKey1);
    hashKey2.WithAttributeName(sortKey).WithAttributeType(
            Aws::DynamoDB::Model::ScalarAttributeType::S);
    request.AddAttributeDefinitions(hashKey2);

    Aws::DynamoDB::Model::KeySchemaElement keySchemaElement1, keySchemaElement2;
    keySchemaElement1.WithAttributeName(partitionKey).WithKeyType(
            Aws::DynamoDB::Model::KeyType::HASH);
    request.AddKeySchema(keySchemaElement1);
    keySchemaElement2.WithAttributeName(sortKey).WithKeyType(
            Aws::DynamoDB::Model::KeyType::RANGE);
    request.AddKeySchema(keySchemaElement2);

    Aws::DynamoDB::Model::ProvisionedThroughput throughput;
    throughput.WithReadCapacityUnits(5).WithWriteCapacityUnits(5);
    request.SetProvisionedThroughput(throughput);

    request.SetTableName(tableName);

    const Aws::DynamoDB::Model::CreateTableOutcome &outcome = dynamoClient.CreateTable(
            request);
    if (outcome.IsSuccess()) {
        std::cout << "Table \""
                  << outcome.GetResult().GetTableDescription().GetTableName() <<
                  "\" was created!" << std::endl;
    }
    else {
        std::cerr << "Failed to create table:" << outcome.GetError().GetMessage()
                  << std::endl;
        return false;
    }

    return waitTableActive(tableName, dynamoClient);
}
```

请参阅上的[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/create_table_composite_key.cpp) GitHub。

## 列出表
<a name="dynamodb-list-tables"></a>

您可以通过调用 [DynamoDB 客户端](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)的 `ListTables` 方法列出特定区域中的表。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/core/utils/Outcome.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/ListTablesRequest.h>
#include <aws/dynamodb/model/ListTablesResult.h>
#include <iostream>
```

 **代码** 

```
//! List the Amazon DynamoDB tables for the current AWS account.
/*!
  \sa listTables()
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
 */

bool AwsDoc::DynamoDB::listTables(
        const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    Aws::DynamoDB::Model::ListTablesRequest listTablesRequest;
    listTablesRequest.SetLimit(50);
    do {
        const Aws::DynamoDB::Model::ListTablesOutcome &outcome = dynamoClient.ListTables(
                listTablesRequest);
        if (!outcome.IsSuccess()) {
            std::cout << "Error: " << outcome.GetError().GetMessage() << std::endl;
            return false;
        }

        for (const auto &tableName: outcome.GetResult().GetTableNames())
            std::cout << tableName << std::endl;
        listTablesRequest.SetExclusiveStartTableName(
                outcome.GetResult().GetLastEvaluatedTableName());

    } while (!listTablesRequest.GetExclusiveStartTableName().empty());

    return true;
}
```

默认情况下，每个调用返回最多 100 个表。在返回的[ListTablesOutcome](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)对象`GetExclusiveStartTableName`上使用以获取最后一个被评估的表。可使用此值在上一列出的最后一个返回值后开始列出。

请参阅[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/list_tables.cpp)。

## 检索有关表的信息
<a name="dynamodb-describe-table"></a>

您可以通过调用 [DynamoDB 客户端](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)的 `DescribeTable` 方法来了解有关表的更多信息。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/DescribeTableRequest.h>
#include <iostream>
```

 **代码** 

```
//! Describe an Amazon DynamoDB table.
/*!
  \sa describeTable()
  \param tableName: The DynamoDB table name.
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
*/
bool AwsDoc::DynamoDB::describeTable(const Aws::String &tableName,
                                     const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    Aws::DynamoDB::Model::DescribeTableRequest request;
    request.SetTableName(tableName);

    const Aws::DynamoDB::Model::DescribeTableOutcome &outcome = dynamoClient.DescribeTable(
            request);

    if (outcome.IsSuccess()) {
        const Aws::DynamoDB::Model::TableDescription &td = outcome.GetResult().GetTable();
        std::cout << "Table name  : " << td.GetTableName() << std::endl;
        std::cout << "Table ARN   : " << td.GetTableArn() << std::endl;
        std::cout << "Status      : "
                  << Aws::DynamoDB::Model::TableStatusMapper::GetNameForTableStatus(
                          td.GetTableStatus()) << std::endl;
        std::cout << "Item count  : " << td.GetItemCount() << std::endl;
        std::cout << "Size (bytes): " << td.GetTableSizeBytes() << std::endl;

        const Aws::DynamoDB::Model::ProvisionedThroughputDescription &ptd = td.GetProvisionedThroughput();
        std::cout << "Throughput" << std::endl;
        std::cout << "  Read Capacity : " << ptd.GetReadCapacityUnits() << std::endl;
        std::cout << "  Write Capacity: " << ptd.GetWriteCapacityUnits() << std::endl;

        const Aws::Vector<Aws::DynamoDB::Model::AttributeDefinition> &ad = td.GetAttributeDefinitions();
        std::cout << "Attributes" << std::endl;
        for (const auto &a: ad)
            std::cout << "  " << a.GetAttributeName() << " (" <<
                      Aws::DynamoDB::Model::ScalarAttributeTypeMapper::GetNameForScalarAttributeType(
                              a.GetAttributeType()) <<
                      ")" << std::endl;
    }
    else {
        std::cerr << "Failed to describe table: " << outcome.GetError().GetMessage();
    }

    return outcome.IsSuccess();
}
```

请参阅上的[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/describe_table.cpp) GitHub。

## 修改表
<a name="dynamodb-update-table"></a>

您可以通过调用 [DynamoDB 客户端](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)的 `UpdateTable` 方法随时修改表的预置吞吐量值。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/core/utils/Outcome.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/ProvisionedThroughput.h>
#include <aws/dynamodb/model/UpdateTableRequest.h>
#include <iostream>
```

 **代码** 

```
//! Update a DynamoDB table.
/*!
  \sa updateTable()
  \param tableName: Name for the DynamoDB table.
  \param readCapacity: Provisioned read capacity.
  \param writeCapacity: Provisioned write capacity.
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
 */
bool AwsDoc::DynamoDB::updateTable(const Aws::String &tableName,
                                   long long readCapacity, long long writeCapacity,
                                   const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    std::cout << "Updating " << tableName << " with new provisioned throughput values"
              << std::endl;
    std::cout << "Read capacity : " << readCapacity << std::endl;
    std::cout << "Write capacity: " << writeCapacity << std::endl;

    Aws::DynamoDB::Model::UpdateTableRequest request;
    Aws::DynamoDB::Model::ProvisionedThroughput provisionedThroughput;
    provisionedThroughput.WithReadCapacityUnits(readCapacity).WithWriteCapacityUnits(
            writeCapacity);
    request.WithProvisionedThroughput(provisionedThroughput).WithTableName(tableName);

    const Aws::DynamoDB::Model::UpdateTableOutcome &outcome = dynamoClient.UpdateTable(
            request);
    if (outcome.IsSuccess()) {
        std::cout << "Successfully updated the table." << std::endl;
    } else {
        const Aws::DynamoDB::DynamoDBError &error = outcome.GetError();
        if (error.GetErrorType() == Aws::DynamoDB::DynamoDBErrors::VALIDATION &&
            error.GetMessage().find("The provisioned throughput for the table will not change") != std::string::npos) {
            std::cout << "The provisioned throughput for the table will not change." << std::endl;
        } else {
            std::cerr << outcome.GetError().GetMessage() << std::endl;
            return false;
        }
    }

    return waitTableActive(tableName, dynamoClient);
}
```

请参阅[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/update_table.cpp)。

## 删除表
<a name="dynamodb-delete-table"></a>

调用 [DynamoDB 客户端](https://docs.aws.amazon.com/sdk-for-cpp/latest/api/aws-cpp-sdk-dynamodb/html/class_aws_1_1_dynamo_d_b_1_1_dynamo_d_b_client.html)的 `DeleteTable` 方法，并向其传递表名称。

 **包含** 

```
#include <aws/core/Aws.h>
#include <aws/dynamodb/DynamoDBClient.h>
#include <aws/dynamodb/model/DeleteTableRequest.h>
#include <iostream>
```

 **代码** 

```
//! Delete an Amazon DynamoDB table.
/*!
  \sa deleteTable()
  \param tableName: The DynamoDB table name.
  \param clientConfiguration: AWS client configuration.
  \return bool: Function succeeded.
*/
bool AwsDoc::DynamoDB::deleteTable(const Aws::String &tableName,
                                   const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::DynamoDB::DynamoDBClient dynamoClient(clientConfiguration);

    Aws::DynamoDB::Model::DeleteTableRequest request;
    request.SetTableName(tableName);

    const Aws::DynamoDB::Model::DeleteTableOutcome &result = dynamoClient.DeleteTable(
            request);
    if (result.IsSuccess()) {
        std::cout << "Your table \""
                  << result.GetResult().GetTableDescription().GetTableName()
                  << " was deleted.\n";
    }
    else {
        std::cerr << "Failed to delete table: " << result.GetError().GetMessage()
                  << std::endl;
    }

    return result.IsSuccess();
}
```

请参阅上的[完整示例](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/cpp/example_code/dynamodb/delete_table.cpp) GitHub。

## 更多信息
<a name="more-info"></a>
+  《Amazon DynamoDB 开发人员指南》中的[表处理准则](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GuidelinesForTables.html)
+  《Amazon DynamoDB 开发人员指南》中的[使用 DynamoDB 中的表](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/WorkingWithTables.html)