NodeJS 和 MongoDB 中的异步故障

Question

i'm trying to create an array which should have an items with open quotation. i have an Items DB in Mongo with key "open_quotation", if there is no quotation for this item => open_quotation: null. i want to map all the array items and to check if there is any open quotations for this item, if there are an open quotation - i want to push it to another array, whihc I created, and to send to client. the problem that when i do map method on items array it is an async function and i get an array already after that the response has been send... so the client receive it as an empty array. pls help to solve this problem.

const{items}= req.body;
const quotations=[];
items.map(async item=>{ const i=await Item.findOne({_id: item._id})
if(i){
`if(i.openquotation){ quotations.push(i)}`
return
)}
res.send({response: true, quotations:quotations}) 



`````

Answer 1

Can you try that:

try {
    const response = await Promise.all(items.map(item => Item.findOne({_id: item._id})));
    const quotations = response.filter((elem) => !!elem.openquotation);
    res.send({ response: true, quotations });
} catch (error) {
    res.send({ response: false, error });
}

Answer 2

you can use async and q module for find query in loop

when you run mainFunction() , mainFunction calls getData()

let async = require('async');
let q = require('q');

const mainFunctio = async()=>{
  const{items}= req.body
  console.log("start")
  resultFromFindLoob  = await getData(items)
  console.log("finish");
  console.log(resultFromFindLoob)
}


const getData = async (items)=>{
  let defer =q.defer();
  let result = []
  async.eachSeries(items , async(item)=>{ // like a for
    try {
      let i = await Item.findOne({_id: item._id}).lean();
      //do something for result (processing)
      if(i)
      result.push(i)
    } catch (error) {
      console.log(error)
    }
  },()=>{ //callback when finish loop
    console.log("finish findone() loop")
    defer.resolve(result)//return the result
  })
  return defer.promise
}

mainFunctio()

restult of mainFunction() based on console.log

1.start mainFunction
2.start getData
3.finish find loop getData
4.finish mainFunction
5.final result : .....