在 Amazon CDK 中引用 TableStreamArn

Posted 2023-02-18

【中文标题】在 Amazon CDK 中引用 TableStreamArn

【英文标题】：Referencing TableStreamArn in Amazon CDK

【发布时间】：2022-01-17 21:14:14

【问题描述】：

我有以下配置：

    //DynamoDB Table
    const table = new dynamodb.Table(this, `DataStore`, 
      tableName: `$StackConfiguration.appName-data-$StackConfiguration.environmentKey`,
      partitionKey:  name: 'scope', type: dynamodb.AttributeType.STRING ,
      sortKey:  name: 'id', type: dynamodb.AttributeType.STRING ,
      readCapacity: 5,
      writeCapacity: 5,
      removalPolicy: cdk.RemovalPolicy.DESTROY,
      stream: StreamViewType.NEW_IMAGE
      
    );

    // Define Call Scaler Lambda
    const callScalerLambda = new lambda.Function(this, 'CallLambdaHandler', 
      description: 'Call Scaler Document Aggregate Lambda',
      functionName: `$StackConfiguration.appName-call-scaler-$StackConfiguration.environmentKey`,
      runtime: lambda.Runtime.PYTHON_3_8, // execution environment
      handler: 'call-scaler/call_lambda.lambda_handler', // file is myLambda, function is lambda_handler
      code: lambda.Code.fromAsset('lambda'), // code loaded from the "lambda" directory
      role: myIAMRole,
      environment: 
        ENVIRONMENT: StackConfiguration.environmentKey,
        SCALERENV: StackConfiguration.scalerEnvironment,
        SYSTEMUSERNAME: StackConfiguration.systemUserName,
        SYSTEMUSERPASS: StackConfiguration.systemUserPass
        
      ,
    );

    const DocumentAggregateCallScalerEventTrigger = new lambda.EventSourceMapping(this, 'DocumentEventTrigger', 
      target:callScalerLambda,
    
      // the properties below are optional
      batchSize: 1,
      enabled: true,
      eventSourceArn: table.tableStreamArn,
      startingPosition: lambda.StartingPosition.LATEST
    );

我试图通过DocumentAggregateCallScalerEventTrigger 简单地定义一个EventSourceTrigger，并将eventSourceArn 定义为表的streamArn。但是，我继续收到以下错误：

error   13-Dec-2021 15:23:39    FAIL test/stack.test.ts
error   13-Dec-2021 15:23:39      ● Test suite failed to run
error   13-Dec-2021 15:23:39    
error   13-Dec-2021 15:23:39        [96mlib/stack.ts[0m:[93m206[0m:[93m7[0m - [91merror[0m[90m TS2322: [0mType 'string | undefined' is not assignable to type 'string'.
error   13-Dec-2021 15:23:39          Type 'undefined' is not assignable to type 'string'.
error   13-Dec-2021 15:23:39    
error   13-Dec-2021 15:23:39        [7m206[0m       eventSourceArn: table.tableStreamArn,
error   13-Dec-2021 15:23:39        [7m   [0m [91m      ~~~~~~~~~~~~~~[0m
error   13-Dec-2021 15:23:39    
error   13-Dec-2021 15:23:39          [96mnode_modules/@aws-cdk/aws-lambda/lib/event-source-mapping.d.ts[0m:[93m9[0m:[93m14[0m
error   13-Dec-2021 15:23:39            [7m9[0m     readonly eventSourceArn: string;
error   13-Dec-2021 15:23:39            [7m [0m [96m             ~~~~~~~~~~~~~~[0m
error   13-Dec-2021 15:23:39            The expected type comes from property 'eventSourceArn' which is declared here on type 'EventSourceMappingProps'

如何在 CDK 中正确引用表的 StreamArn？

【参考方案1】：

就 Typescript 而言，table.tableStreamArn 是一个可选字符串 (string | undefined)，因此它不允许您将其分配给必需的 eventSourceArn 属性。实际上，table.tableStreamArn 将解析为字符串，因为您已在表格上设置了 stream 属性。但是 Typescript 无法自己解决这个问题。

有多种方法可以让 Typescript 变得快乐，其中一些比其他更优雅：例如，您可以使用 table.tableStreamArn! 断言非空值，或者强制使用字符串 table?.tableStreamArn ?? 'SHOULD NOT HAPPEN'。要么 如果未定义则抛出错误。

另一种选择是在 lambda 上添加事件源，这样可以避免整个问题：

import * as evtsrc from '@aws-cdk/aws-lambda-event-sources';

callScalerLambda.addEventSource(
  new evtsrc.DynamoEventSource(table, 
    batchSize: 1,
    enabled: true,
    startingPosition: lambda.StartingPosition.LATEST,
  )
);