使用DataMapper从DynamoDB获取数据时触发运行时错误

扫描操作错误 #

2023-01-04T20:02:56.603Z 1ef44a6b-8b4f-51c5-bd10-164456efc703 ERROR Invoke Error {
"errorType": "TypeError",
"errorMessage": "this.client.scan(...).promise is not a function",
"stack": [
"TypeError: this.client.scan(...).promise is not a function",
" at ScanPaginator.getNext (/var/task/node_modules/@aws/dynamodb-query-iterator/build/ScanPaginator.js:17:18)",
" at /var/task/node_modules/@aws/dynamodb-query-iterator/build/DynamoDbPaginator.js:60:26"
] }

获取操作错误 #

{
"errorType": "Runtime.UnhandledPromiseRejection",
"errorMessage": "TypeError: _b.map is not a function",
"reason": {
"errorType": "TypeError",
"errorMessage": "_b.map is not a function",
"stack": [
"TypeError: _b.map is not a function",
" at /var/task/node_modules/@aws-sdk/middleware-user-agent/dist-cjs/user-agent-middleware.js:14:151",
" at async /var/task/node_modules/@aws-sdk/middleware-logger/dist-cjs/loggerMiddleware.js:5:22"
]
},
"promise": {},
"stack": [
"Runtime.UnhandledPromiseRejection: TypeError: _b.map is not a function",
" at process. (file:///var/runtime/index.mjs:1194:17)",
" at process.emit (node:events:513:28)",
" at emit (node:internal/process/promises:149:20)",
" at processPromiseRejections (node:internal/process/promises:283:27)",
" at process.processTicksAndRejections (node:internal/process/task_queues:96:32)"
] }

用到的代码 #

DTO定义 #

@table("Configs")
export class Configs {
    @hashKey()
    configId!: string;

    @attribute()
    groupName!: string
}

Lambda Handler代码 #

import {SQSEvent} from "aws-lambda";
import {DynamoDB} from "@aws-sdk/client-dynamodb"
import {DataMapper} from "@aws/dynamodb-data-mapper";
import {Configs} from "./models/Configs";

const client = new DynamoDB({region: "us-east-1"});
const mapper = new DataMapper({client});

export const handler = async (sqsEvent: SQSEvent) => {
    console.log(`Event: ${JSON.stringify(sqsEvent, null, 2)}`);
    for (let record of sqsEvent.Records) {
        let messageBody = record.body;
        console.log("MessageBody: " + messageBody);
    }
    const config = new Configs();

    for await (const item of mapper.scan(Configs)) {
        console.log('scan result', item);
    }

    console.log("done scanning");

    mapper.get(Object.assign(new Configs(), {id: 'MY_ID'}))
        .then(myItem => {
            console.log('MyItem from db: ', myItem);
        })
        .catch(err => {
            console.log("Not found");
        })
};

tsconfig.json配置 #

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "target": "es2020",
    "strict": true,
    "preserveConstEnums": true,
    "outDir": "./dist/lib",
    "module": "CommonJS",
    "declaration": true,
    "declarationDir": "./dist/types",
    "sourceMap": false,
    "moduleResolution":"node",
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "isolatedModules": true,
    "emitDecoratorMetadata": true,
    "typeRoots": [
      "./node_modules/@types"
    ]
  },
  "exclude": [
    "./node_modules", "**/*.test.ts"]
}

问题原因与解决办法 #

核心问题：SDK版本不兼容 #

@aws/dynamodb-data-mapper 基于AWS SDK v2开发，而你使用的是AWS SDK v3的@aws-sdk/client-dynamodb，两者API逻辑不兼容：

• v2的DynamoDB客户端方法（如scan）返回的对象自带.promise()方法，v3客户端返回的是命令对象，需用send方法调用，无.promise()，直接触发扫描错误。
• _b.map错误也是v3中间件与data-mapper的v2逻辑不兼容导致的。

解决步骤 #

1. 替换SDK为v2版本
   卸载v3客户端，安装v2的aws-sdk：

   npm uninstall @aws-sdk/client-dynamodb
   npm install aws-sdk
   

2. 修改Handler中的导入与客户端初始化
   调整代码导入和客户端创建逻辑：

   import {SQSEvent} from "aws-lambda";
   // 替换v3导入为v2的AWS SDK
   import AWS from "aws-sdk";
   import {DataMapper} from "@aws/dynamodb-data-mapper";
   import {Configs} from "./models/Configs";
   
   // 使用v2的DynamoDB客户端
   const client = new AWS.DynamoDB({region: "us-east-1"});
   const mapper = new DataMapper({client});
   

3. 修正get操作的属性错误
   DTO中哈希键为configId，但代码中用了id: 'MY_ID'，会导致无法匹配数据，需改为：

   mapper.get(Object.assign(new Configs(), {configId: 'MY_ID'}))
       .then(myItem => {
           console.log('MyItem from db: ', myItem);
       })
       .catch(err => {
           console.log("Not found");
       })
   

4. 验证依赖版本
   确保@aws/dynamodb-data-mapper及其关联依赖（如@aws/dynamodb-data-mapper-annotations）为兼容v2的最新版本，避免版本冲突。

内容的提问来源于stack exchange，提问作者AnOldSoul