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# 使用 AWS SDK 查詢具有高度一致讀取的 DynamoDB 資料表
<a name="example_dynamodb_Scenarios_QueryWithStronglyConsistentReads_section"></a>

下列程式碼範例示範如何查詢具有高度一致性讀取的資料表。
+ 設定 DynamoDB 查詢的一致性層級。
+ 使用高度一致性讀取以取得最新的資料。
+ 了解最終一致性與強式一致性之間的權衡。

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#### [ Java ]

**適用於 Java 2.x 的 SDK **  
使用 查詢具有可設定讀取一致性的 DynamoDB 資料表 AWS SDK for Java 2.x。  

```
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.QueryRequest;
import software.amazon.awssdk.services.dynamodb.model.QueryResponse;
import software.amazon.awssdk.services.dynamodb.model.ResourceNotFoundException;

import java.util.HashMap;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

    public QueryResponse queryWithConsistentReads(
        final String tableName,
        final String partitionKeyName,
        final String partitionKeyValue,
        final boolean useConsistentRead) {

        CodeSampleUtils.validateTableParameters(tableName, partitionKeyName, partitionKeyValue);

        // Create expression attribute names for the column names
        final Map<String, String> expressionAttributeNames = new HashMap<>();
        expressionAttributeNames.put(EXPRESSION_ATTRIBUTE_NAME_PK, partitionKeyName);

        // Create expression attribute values for the column values
        final Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
        expressionAttributeValues.put(
            EXPRESSION_ATTRIBUTE_VALUE_PK,
            AttributeValue.builder().s(partitionKeyValue).build());

        // Create the query request
        final QueryRequest queryRequest = QueryRequest.builder()
            .tableName(tableName)
            .keyConditionExpression(KEY_CONDITION_EXPRESSION)
            .expressionAttributeNames(expressionAttributeNames)
            .expressionAttributeValues(expressionAttributeValues)
            .consistentRead(useConsistentRead)
            .build();

        try {
            final QueryResponse response = dynamoDbClient.query(queryRequest);
            LOGGER.log(Level.INFO, "Query successful. Found {0} items", response.count());
            return response;
        } catch (ResourceNotFoundException e) {
            LOGGER.log(Level.SEVERE, "Table not found: {0}", tableName);
            throw e;
        } catch (DynamoDbException e) {
            LOGGER.log(Level.SEVERE, "Error querying with consistent reads", e);
            throw e;
        }
    }
```
+  如需 API 的詳細資訊，請參閱《*AWS SDK for Java 2.x API 參考*》中的 [Query](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/Query)。

------
#### [ JavaScript ]

**適用於 JavaScript (v3) 的 SDK**  
使用 查詢具有可設定讀取一致性的 DynamoDB 資料表 適用於 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;
  }
}
```
+  如需 API 的詳細資訊，請參閱《*適用於 JavaScript 的 AWS SDK API 參考*》中的 [Query](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/QueryCommand)。

------
#### [ Python ]

**適用於 Python 的 SDK (Boto3)**  
使用 的強式一致讀取選項查詢 DynamoDB 資料表 適用於 Python (Boto3) 的 AWS SDK。  

```
import time

import boto3
from boto3.dynamodb.conditions import Key


def query_with_consistent_read(
    table_name,
    partition_key_name,
    partition_key_value,
    sort_key_name=None,
    sort_key_value=None,
    consistent_read=True,
):
    """
    Query a DynamoDB table with the option for strongly consistent reads.

    Args:
        table_name (str): The name of the DynamoDB table.
        partition_key_name (str): The name of the partition key attribute.
        partition_key_value (str): The value of the partition key to query.
        sort_key_name (str, optional): The name of the sort key attribute.
        sort_key_value (str, optional): The value of the sort key to query.
        consistent_read (bool, optional): Whether to use strongly consistent reads. Defaults to True.

    Returns:
        dict: The response from DynamoDB containing the query results.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Build the key condition expression
    key_condition = Key(partition_key_name).eq(partition_key_value)

    if sort_key_name and sort_key_value:
        key_condition = key_condition & Key(sort_key_name).eq(sort_key_value)

    # Perform the query with the consistent read option
    response = table.query(KeyConditionExpression=key_condition, ConsistentRead=consistent_read)

    return response
```
+  如需 API 的詳細資訊，請參閱《*適用於 Python (Boto3) 的AWS SDK API 參考*》中的 [Query](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/Query)。

------

如需 AWS SDK 開發人員指南和程式碼範例的完整清單，請參閱 [搭配 AWS SDK 使用 DynamoDB](sdk-general-information-section.md)。此主題也包含有關入門的資訊和舊版 SDK 的詳細資訊。