# 使用 PartiQL for DynamoDB 执行事务
本部分介绍如何使用事务和 PartiQL for DynamoDB。PartiQL 事务限制为总共 100 条语句（操作）。
有关 DynamoDB 事务的更多信息，请参阅[使用 DynamoDB 事务管理复杂工作流](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transactions.html)。
**注意**
整个事务必须由读取语句或写语句组成。您不能在一个事务中混合使用这两个语句。EXISTS 函数是一个例外。可用于检查项目的特定属性的条件，类似于 [TransactWriteItems](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transaction-apis.html#transaction-apis-txwriteitems) API 操作中 `ConditionCheck` 的方式。
**Topics**
+ [
## 语法
](#ql-reference.multiplestatements.transactions.syntax)
+ [
## 参数
](#ql-reference.multiplestatements.transactions.parameters)
+ [
## 返回值
](#ql-reference.multiplestatements.transactions.return)
+ [
## 示例
](#ql-reference.multiplestatements.transactions.examples)
## 语法
```
[
{
"Statement":" statement ",
"Parameters":[
{
" parametertype " : " parametervalue "
}, ...]
} , ...
]
```
## 参数
***语句***
（必需）PartiQL for DynamoDB 支持的语句。
整个事务必须由读取语句或写语句组成。您不能在一个事务中混合使用这两个语句。
***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。
## 返回值
此语句不会返回写入操作（INSERT、UPDATE 或 DELETE）的任何值。但是，根据 WHERE 子句中指定的条件，它会为读取操作 (SELECT) 返回不同的值。
**注意**
如果任何单例 INSERT、UPDATE 或 DELETE 操作返回错误，则取消事务并抛出 `TransactionCanceledException` 异常，取消原因代码包括来自各个单例操作的错误。
## 示例
以下示例运行作为事务的多条语句。
------
#### [ AWS CLI ]
1. 将以下 JSON 代码保存到名为 partiql.json 的文件
```
[
{
"Statement": "EXISTS(SELECT * FROM \"Music\" where Artist='No One You Know' and SongTitle='Call Me Today' and Awards is MISSING)"
},
{
"Statement": "INSERT INTO Music value {'Artist':?,'SongTitle':'?'}",
"Parameters": [{\"S\": \"Acme Band\"}, {\"S\": \"Best Song\"}]
},
{
"Statement": "UPDATE \"Music\" SET AwardsWon=1 SET 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 execute-transaction --transact-statements file://partiql.json
```
------
#### [ Java ]
```
public class DynamoDBPartiqlTransaction {
public static void main(String[] args) {
// Create the DynamoDB Client with the region you want
AmazonDynamoDB dynamoDB = createDynamoDbClient("us-west-2");
try {
// Create ExecuteTransactionRequest
ExecuteTransactionRequest executeTransactionRequest = createExecuteTransactionRequest();
ExecuteTransactionResult executeTransactionResult = dynamoDB.executeTransaction(executeTransactionRequest);
System.out.println("ExecuteTransaction successful.");
// Handle executeTransactionResult
} catch (Exception e) {
handleExecuteTransactionErrors(e);
}
}
private static AmazonDynamoDB createDynamoDbClient(String region) {
return AmazonDynamoDBClientBuilder.standard().withRegion(region).build();
}
private static ExecuteTransactionRequest createExecuteTransactionRequest() {
ExecuteTransactionRequest request = new ExecuteTransactionRequest();
// Create statements
List statements = getPartiQLTransactionStatements();
request.setTransactStatements(statements);
return request;
}
private static List getPartiQLTransactionStatements() {
List statements = new ArrayList();
statements.add(new ParameterizedStatement()
.withStatement("EXISTS(SELECT * FROM "Music" where Artist='No One You Know' and SongTitle='Call Me Today' and Awards is MISSING)"));
statements.add(new ParameterizedStatement()
.withStatement("INSERT INTO "Music" value {'Artist':'?','SongTitle':'?'}")
.withParameters(new AttributeValue("Acme Band"),new AttributeValue("Best Song")));
statements.add(new ParameterizedStatement()
.withStatement("UPDATE "Music" SET AwardsWon=1 SET AwardDetail={'Grammys':[2020, 2018]} where Artist='Acme Band' and SongTitle='PartiQL Rocks'"));
return statements;
}
// Handles errors during ExecuteTransaction execution. Use recommendations in error messages below to add error handling specific to
// your application use-case.
private static void handleExecuteTransactionErrors(Exception exception) {
try {
throw exception;
} catch (TransactionCanceledException tce) {
System.out.println("Transaction Cancelled, implies a client issue, fix before retrying. Error: " + tce.getErrorMessage());
} catch (TransactionInProgressException tipe) {
System.out.println("The transaction with the given request token is already in progress, consider changing " +
"retry strategy for this type of error. Error: " + tipe.getErrorMessage());
} catch (IdempotentParameterMismatchException ipme) {
System.out.println("Request rejected because it was retried with a different payload but with a request token that was already used, " +
"change request token for this payload to be accepted. Error: " + ipme.getErrorMessage());
} catch (Exception e) {
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());
}
}
}
```
------
以下示例显示了 DynamoDB 读取具有 WHERE 子句中所指定不同条件的项目时的不同返回值。
------
#### [ AWS CLI ]
1. 将以下 JSON 代码保存到名为 partiql.json 的文件
```
[
// Item exists and projected attribute exists
{
"Statement": "SELECT * FROM "Music" WHERE Artist='No One You Know' and SongTitle='Call Me Today'"
},
// Item exists but projected attributes do not exist
{
"Statement": "SELECT non_existent_projected_attribute FROM "Music" WHERE Artist='No One You Know' and SongTitle='Call Me Today'"
},
// Item does not exist
{
"Statement": "SELECT * FROM "Music" WHERE Artist='No One I Know' and SongTitle='Call You Today'"
}
]
```
1. 命令提示符中的以下命令。
```
aws dynamodb execute-transaction --transact-statements file://partiql.json
```
1. 如果成功，将返回以下响应。
```
{
"Responses": [
// Item exists and projected attribute exists
{
"Item": {
"Artist":{
"S": "No One You Know"
},
"SongTitle":{
"S": "Call Me Today"
}
}
},
// Item exists but projected attributes do not exist
{
"Item": {}
},
// Item does not exist
{}
]
}
```
------