如何正确使用 Promise.all 组合两个数据集并返回单个对象？

Question

I have an existing object data . I am using NodeJS async function to retrieve value of fetchResponse . Finally, I am trying to embed the fetchResponse to the existing data object using the following for loop

for (let key in data) {
    for (let number in data[key]) {
        data[key][number].map( async d=> {
            const fetchResponse = await sequelize
                .query(await fetchHostDetails(d.Hostname), options);
        data[key][number]['Fetchresult'] =  fetchResponse;
        });
    }
}
return data;

I see that data is still having the original value and not including the key value pair Fetchresult : fetchResponse

I am trying to use Promise.All as below but it is still giving original data object value.

for (let key in data) {
    for (let number in data[key]) {
        data[key][number].map( async d=> {
            const fetchResponse = await sequelize
                .query(await fetchHostDetails(d.Hostname), options);
             await Promise.all({...d, Fetchresult : fetchResponse});
        });
    }
}
return data;

const data =
{
  "error1": {
    "7": [
      {
        "ErrorType": "Error-1A",
        "Hostname": "host123.com"
      }
    ],
    "8": [
      {
        "ErrorType": "Error-1B",
        "Hostname": "host223.com"
      },
      {
        "ErrorType": "Error-1C",
        "Hostname": "host1231.com"
      }
    ]
  }
}

I am getting below fetchResponse for hostName under Error-1A

const fetchResponse =
    [
      {
        "resType": "unknow data",
        "res": "missing data"
      },
      {
        "resType": "login failed",
        "res": "login with wrong userid"
      }
    ]

Similarly there will be separate fetchResponse for hostName under Error-1b and Error-1C but response format will be similar to what we have got for Error-1A .

For data.error1[8] we are getting 2 values of fetchResponse but please note that those are 2 separate values for Error-1B and Error-1C . One will be displayed after Error-1B and other will be displayed after Error-1C .

Answer 1

It doesn't make sense to me to use await in a loop. I'd prefer to generate a single, flat list of promises to eventually have one Promise.all that awaits them all.

Allow me to use a placeholderAsyncOperation to stand in for your fetch using the key and number. For demonstration purposes, I'll just delay a bit and then returns some object based on the parameters. I'll use your original input data though.

 const data = { "error1": { "7": [ { "ErrorType": "Error-1A", "Hostnames": "host123.com,hostabc.com,host33a.com..." } ], "8": [ { "ErrorType": "Error-1B", "Hostnames": "host223.com,host2c.com,host43a.com..." }, { "ErrorType": "Error-1C", "Hostnames": "host1231.com,host2abc.com,host313a.com..." } ] }, "error2": { }, "error3": { } } async function placeholderAsyncOperation(key, number, result) { await delay(1000); return {key, number, resultJSON: JSON.stringify(result)}; } const delay = time_ms => new Promise(resolve => setTimeout(resolve, time_ms)); let promises = []; for (let key in data) { for (let number in data[key]) { promises.push(data[key][number].map(val => (placeholderAsyncOperation(key, number, val)))); } } Promise.all(promises.flat()).then(result => console.table(result));

NOTE: About this snippet:

This uses console.table that Stack Overflow doesn't support so well yet (output embedded into the page will appear empty), so if you run this snippet in your browser you'll likely have to open your browser's built-in console before running the snippet . Like, by pressing F12 or however your browser shows its console.

Answer 2

I would first of all build an array containing all the promises, along with key and index:

let promises = [];

for (let key in data) {
  for (let number in data[key]) {
      let p = async() => {
           const fetchResponse = await sequelize.query(
               await fetchHostDetails(d.Hostname), options
           );
           return {key, number, fetchResponse};
      };
      promises.push(p);
   }
}

Now, before you inject this "fetch" data into your original data, the promises need to resolve. So we use an async function:

const merge = async (data, promises) => {
    
    // wait for all promises
    const resolvedPromises = await Promise.all(promises);

    // inject the results into "data"
    resolvedPromises.forEach(row => {
        if (row) {
            const {key, number, fetchResponse} = row;
            data[key][number]['Fetchresult'] =  fetchResponse;
        }
    });

    return data;

};

When you call this, remember it's async:

merge(data, promises).then(newData => {

   console.log(newData);

});