# 对 PartiQL for DynamoDB 运行批处理操作
<a name="ql-reference.multiplestatements.batching"></a>

本部分介绍如何使用处理器操作和 PartiQL for DynamoDB。

**注意**  
整个批处理必须由读取语句或写入语句组成；不能在一个批处理中混合使用这两种语句。
`BatchExecuteStatement` 和 `BatchWriteItem` 每批可执行的语句不超过 25 个。
`BatchExecuteStatement` 利用 `BatchGetItem`，后者在单独的语句中获取主键的列表。

**Topics**
+ [语法](#ql-reference.multiplestatements.batching.syntax)
+ [参数](#ql-reference.multiplestatements.batching.parameters)
+ [示例](#ql-reference.multiplestatements.batching.examples)

## 语法
<a name="ql-reference.multiplestatements.batching.syntax"></a>

```
[
  {
    "Statement": "SELECT pk FROM ProblemSet WHERE pk = 'p#9StkWHYTxm7x2AqSXcrfu7' AND sk = 'info'"
  },
  {
    "Statement": "SELECT pk FROM ProblemSet WHERE pk = 'p#isC2ChceGbxHgESc4szoTE' AND sk = 'info'"
  }
]
```

```
[
   {
      "Statement":"{{ statement }}",
      "Parameters":[
         {
            "{{ parametertype }}" : "{{ parametervalue }}"
         }, ...]
   } , ...
]
```

## 参数
<a name="ql-reference.multiplestatements.batching.parameters"></a>

**{{语句}}**  
（必需）PartiQL for DynamoDB 支持的语句。  
+ 整个批处理必须由读取语句或写入语句组成；不能在一个批处理中混合使用这两种语句。
+ `BatchExecuteStatement` 和 `BatchWriteItem` 每批可执行的语句不超过 25 个。

**{{parametertype}}**  
（可选）DynamoDB 类型，如果在指定 PartiQL 语句时使用了参数。

**{{parametervalue}}**  
（可选）如果在指定 PartiQL 语句时使用了参数，则为参数值。

## 示例
<a name="ql-reference.multiplestatements.batching.examples"></a>

------
#### [ Amazon CLI ]

1. 将以下 json 保存到一个名为 partiql.json 的文件

   ```
   [
      {
   	 "Statement": "INSERT INTO Music VALUE {'Artist':?,'SongTitle':?}",
   	  "Parameters": [{"S": "Acme Band"}, {"S": "Best Song"}]
   	},
   	{
   	 "Statement": "UPDATE Music SET AwardsWon=1, AwardDetail={'Grammys':[2020, 2018]} WHERE Artist='Acme Band' AND SongTitle='PartiQL Rocks'"
       }
   ]
   ```

1. 在命令提示符中运行以下命令。

   ```
   aws dynamodb batch-execute-statement  --statements  file://partiql.json
   ```

------
#### [ Java ]

```
public class DynamoDBPartiqlBatch {

    public static void main(String[] args) {
        // Create the DynamoDB Client with the region you want
        AmazonDynamoDB dynamoDB = createDynamoDbClient("us-west-2");
        
        try {
            // Create BatchExecuteStatementRequest
            BatchExecuteStatementRequest batchExecuteStatementRequest = createBatchExecuteStatementRequest();
            BatchExecuteStatementResult batchExecuteStatementResult = dynamoDB.batchExecuteStatement(batchExecuteStatementRequest);
            System.out.println("BatchExecuteStatement successful.");
            // Handle batchExecuteStatementResult

        } catch (Exception e) {
            handleBatchExecuteStatementErrors(e);
        }
    }

    private static AmazonDynamoDB createDynamoDbClient(String region) {

        return AmazonDynamoDBClientBuilder.standard().withRegion(region).build();
    }

    private static BatchExecuteStatementRequest createBatchExecuteStatementRequest() {
        BatchExecuteStatementRequest request = new BatchExecuteStatementRequest();

        // Create statements
        List<BatchStatementRequest> statements = getPartiQLBatchStatements();

        request.setStatements(statements);
        return request;
    }

    private static List<BatchStatementRequest> getPartiQLBatchStatements() {
        List<BatchStatementRequest> statements = new ArrayList<BatchStatementRequest>();

        statements.add(new BatchStatementRequest()
                               .withStatement("INSERT INTO Music value {'Artist':'Acme Band','SongTitle':'PartiQL Rocks'}"));

        statements.add(new BatchStatementRequest()
                               .withStatement("UPDATE Music set AwardDetail.BillBoard=[2020] where Artist='Acme Band' and SongTitle='PartiQL Rocks'"));

        return statements;
    }

    // Handles errors during BatchExecuteStatement execution. Use recommendations in error messages below to add error handling specific to 
    // your application use-case.
    private static void handleBatchExecuteStatementErrors(Exception exception) {
        try {
            throw exception;
        } catch (Exception e) {
            // There are no API specific errors to handle for BatchExecuteStatement, common DynamoDB API errors are handled below
            handleCommonErrors(e);
        }
    }

    private static void handleCommonErrors(Exception exception) {
        try {
            throw exception;
        } catch (InternalServerErrorException isee) {
            System.out.println("Internal Server Error, generally safe to retry with exponential back-off. Error: " + isee.getErrorMessage());
        } catch (RequestLimitExceededException rlee) {
            System.out.println("Throughput exceeds the current throughput limit for your account, increase account level throughput before " + 
                "retrying. Error: " + rlee.getErrorMessage());
        } catch (ProvisionedThroughputExceededException ptee) {
            System.out.println("Request rate is too high. If you're using a custom retry strategy make sure to retry with exponential back-off. " +
                "Otherwise consider reducing frequency of requests or increasing provisioned capacity for your table or secondary index. Error: " + 
                ptee.getErrorMessage());
        } catch (ResourceNotFoundException rnfe) {
            System.out.println("One of the tables was not found, verify table exists before retrying. Error: " + rnfe.getErrorMessage());
        } catch (AmazonServiceException ase) {
            System.out.println("An AmazonServiceException occurred, indicates that the request was correctly transmitted to the DynamoDB " + 
                "service, but for some reason, the service was not able to process it, and returned an error response instead. Investigate and " +
                "configure retry strategy. Error type: " + ase.getErrorType() + ". Error message: " + ase.getErrorMessage());
        } catch (AmazonClientException ace) {
            System.out.println("An AmazonClientException occurred, indicates that the client was unable to get a response from DynamoDB " +
                "service, or the client was unable to parse the response from the service. Investigate and configure retry strategy. "+
                "Error: " + ace.getMessage());
        } catch (Exception e) {
            System.out.println("An exception occurred, investigate and configure retry strategy. Error: " + e.getMessage());
        }
    }

}
```

------