嵌套异步等待函数未在 AWS Lambda 函数中执行

Question

问题：我使用异步等待函数的经验很少，我试图在 if-else 语句中执行嵌套的异步等待函数，该语句依赖于更高级别的异步函数在事件检测时执行。我希望从嵌套的异步函数返回成功的 http 响应，但我继续为响应获取空值。然而，嵌套的异步函数在 if-else 语句之外按预期工作。我的目标是简单地将代码的“等待新承诺”部分获取到 return 条件 if-else 语句中的 http 响应。对此的任何帮助表示赞赏。

我的尝试：除了搜索具有类似问题的问题外，我没有真正尝试过任何补救措施，因为我对异步等待函数的性质知之甚少。

代码：

 exports.handler = async (event) => {
    
    const sensorId = event.sensorId;
    
    ddb.scan(params, function (err, data) {
  

    if (err) {
    console.log("Error", err);
  } else {
    console.log("Success", data);
    console.log(typeof(data));
    data.Items.forEach(function (item, index, array) {
      console.log("printing", item);
      console.log('Testing', item.sensorId.S);
      
      if (item.sensorId.S == sensorId) {
          console.log('New sensorId was not created. Already Exists.');
          return ;
      }
      else {
    // Here is the nested async await function
    async () => {
    console.log(event.sensorId);
    const req = new AWS.HttpRequest(appsyncUrl, region);

    const item = {
        input: {
            id: event.sensorId,
            sensorId: event.sensorId
        }
    };

    req.method = "POST";
    req.path = "/graphql";
    req.headers.host = endpoint;
    req.headers["Content-Type"] = "application/json";
    req.body = JSON.stringify({
        query: print(createSensor),
        operationName: "createSensor",
        variables: item
    });
    console.log(typeof(graphqlQuery));
    if (apiKey) {
        req.headers["x-api-key"] = apiKey;
    } else {
        const signer = new AWS.Signers.V4(req, "appsync", true);
        signer.addAuthorization(AWS.config.credentials, AWS.util.date.getDate());
    }
    
    
    const data =  await new Promise((resolve, reject) => {
        const httpRequest = https.request({ ...req, host: endpoint }, (result) => {
            let data = "";

            result.on("data", (chunk) => {
                data += chunk;
            });

            result.on("end", () => {
                resolve(JSON.parse(data.toString()));
            });
        });

        httpRequest.write(req.body);
        httpRequest.end();
    });
  
  


try {
    return {
        statusCode: 200,
        body: data
    };
}

catch(err) {
    console.log('error', err);
}
      };
      
    }});
  }
});

预期结果：

Response
{
  "statusCode": 200,
  "body": {
    "data": {
      "createSensor": {
        "id": "fd78597a-12fd-4bd1-9f9d-6ee1a88e197d",
        "digit": null,
        "date": null,
        "timestamp": null
      }
    }
  }
}

实际结果：

Response
null

Answer 1

您的代码存在一些问题：

嵌套的异步函数 — 您正在创建它但从未执行它

async () => { // creates an async anonymous arrow function, that's it

}

两种解决方案：

// wrapping the function in an IIFE create and executes it
(async () => {

})();

// give it a name and execute it later
async main() => {

}

main();

您可以通过将传递给 forEach 的回调声明为异步来摆脱嵌套的异步函数：

data.Items.forEach(async (item, index, array) => { // <--- this is async
  // ...

  const req = new AWS.HttpRequest(appsyncUrl, region);
  const item = {
    input: {
      id: event.sensorId,
      sensorId: event.sensorId,
    },
  };

  // ...
});

末尾的 try/catch 块不会捕获任何错误。相反，将您创建的 Promise 包装在 try/catch 块中，并在发生错误事件时从内部拒绝：

try {
  const data = await new Promise((resolve, reject) => {
    const httpRequest = https.request(
      { ...req, host: endpoint },
      (result) => {
        // ...

        result.on("error", (error) => {
          reject(error);
        });

        // ...
      }
    );

    // ...
  });

  return {
    statusCode: 200,
    body: data,
  };
} catch (err) {
  console.log("error", err);
}

运行 forEach 内部的异步操作不会执行您打算执行的操作。您可能打算在所有 sensorsId 创建后做出响应。真正发生的是您在创建第一个 sensorId 后立即做出响应。那是因为 forEach 同时触发 data.Items 的回调。一个解决方案是使用 map 和 return 一个 Promise 数组，然后您可以使用 Promise.all.

等待

这是最终代码以及我将如何解决它。作为额外，我已经承诺 ddb.scan 所以你不会将回调与承诺和 async/await:
混在一起
const scanAsync = util.promisify(ddb.scan); exports.handler = async (event) => { const sensorId = event.sensorId; try { const data = await scanAsync(params); const responses = await Promise.all( data.Items.map((item) => { if (item.sensorId.S == sensorId) { console.log("New sensorId was not created. Already Exists."); return; } const req = new AWS.HttpRequest(appsyncUrl, region); const item = { input: { id: event.sensorId, sensorId: event.sensorId, }, }; req.method = "POST"; req.path = "/graphql"; req.headers.host = endpoint; req.headers["Content-Type"] = "application/json"; req.body = JSON.stringify({ query: print(createSensor), operationName: "createSensor", variables: item, }); if (apiKey) { req.headers["x-api-key"] = apiKey; } else { const signer = new AWS.Signers.V4(req, "appsync", true); signer.addAuthorization( AWS.config.credentials, AWS.util.date.getDate() ); } return new Promise((resolve, reject) => { const httpRequest = https.request( { ...req, host: endpoint }, (result) => { let data = ""; result.on("data", (chunk) => { data += chunk; }); result.on("error", (error) => { reject(error); }); result.on("end", () => { resolve(JSON.parse(data.toString())); }); } ); httpRequest.write(req.body); httpRequest.end(); }); }) ); return { statusCode: 200, body: responses, }; } catch (error) { console.log("error", error); } };

希望您能从我的回复中学到一两件事:)。如果您有任何问题，请告诉我。

嵌套异步等待函数未在 AWS Lambda 函数中执行

Nested async await function not executing in AWS Lambda Function

javascript

asynchronous

node.js

async-await

aws-lambda