嵌套異步等待函式未在AWSLambda函式中執行

問題：我幾乎沒有使用異步等待函式的經驗，我試圖在 if-else 陳述句中執行嵌套的異步等待函式，該陳述句依賴于更高級別的異步函式在事件檢測時執行。我希望從嵌套的異步函式中獲得成功的 http 回應，但我繼續獲得回應的空值。但是，嵌套的異步函式在 if-else 陳述句之外按預期作業。我的目標是簡單地獲得代碼的“等待新承諾”部分，以在條件 if-else 陳述句中回傳 http 回應。對此的任何幫助表示贊賞。

我嘗試過什么：除了搜索具有類似問題的問題之外，我還沒有真正嘗試過任何補救措施，因為我對異步等待函式的性質知之甚少。

代碼：

 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);
}
      };
      
    }});
  }
});

預期結果：

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

實際結果：

Response
null

uj5u.com熱心網友回復：

您的代碼存在一些問題：

1. 嵌套的異步函式——你正在創建它但從不執行它

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

}

兩種解決方案：

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

})();

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

}

main();

2. 您可以通過將傳遞給 forEach 的回呼宣告為異步來擺脫嵌套的異步函式：

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,
    },
  };

  // ...
});

3. 最后的 try/catch 塊不會捕獲任何錯誤。相反，將您創建的 Promise 包裝在 try/catch 塊中，并在發生錯誤事件時從內部拒絕：

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);
}

4. 在 forEach 中運行異步操作不會執行您打算執行的操作。您可能打算在創建所有傳感器 ID后做出回應。真正發生的是，您會在創建第一個 sensorId 后立即做出回應。這是因為 forEachdata.Items同時觸發了回呼。一個解決方案是改用 map 并回傳一個 Promise 陣列，然后您可以使用 Promise.all 等待。

這是最終代碼以及我將如何解決它。作為一個額外的我已經承諾ddb.scan，所以你不會將回呼與承諾和異步/等待混合：

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);
  }
};

我希望你從我的回復中學到一兩件事:)。如果您有任何問題，請告訴我。

標籤：javascript 节点.js 异步 aws-lambda 异步等待

上一篇：setTimeout僅用于1次異步呼叫

下一篇：JavaScript：我們可以創建什么型別的函式來異步執行？