Not getting result in node js, mongo db using promise in loop

Question

I am new in nodejs and mongodb. Its really very confusing to use promise in loop in nodejs for new developer.I require the final array or object. which then() give me final result. Please correct this.
I have a controller function described below.

let League = require('../../model/league.model');
let Leaguetype = require('../../model/leagueType.model');
let Leaguecategories = require('../../model/leagueCategories.model');


let fetchLeague = async function (req, res, next){
    let body = req.body;
    await mongo.findFromCollection(Leaguetype)
    .then(function(types) {
        return Promise.all(types.map(function(type){ 
            return mongo.findFromCollection(Leaguecategories, {"league_type_id": type._id})
            .then(function(categories) {
                return Promise.all(categories.map(function(category){
                    return mongo.findFromCollection(League, {"league_category_id": category._id})
                    .then(function(leagues) {
                        return Promise.all(leagues.map(function(league){
                            return league;
                    }))
                    .then(function(league){
                        console.log(league);
                    })
                    })
                }))
            });
        }))

    })
    .then(function(final){
      console.log(final);
    })
    .catch (error => {
      console.log('no',error);
  })
}

mongo.findFromCollection function is looking like this.

findFromCollection = (model_name, query_obj = {}) => {
        return new Promise((resolve, reject) => {
            if (model_name !== undefined && model_name !== '') {
                    model_name.find(query_obj, function (e, result) {

                    if (!e) {
                        resolve(result)
                    } else {
                        reject(e);
                    }
                })
            } else {
                reject({ status: 104, message: `Invalid search.` });
            }
        })
    }

and here is my model file

var mongoose = require('mongoose');
const league_categories = new mongoose.Schema({
        name: {
          type: String,
          required: true
        },
        active: {
          type: String,
          required: true
        },
        create_date: {
          type: Date,
          required: true,
          default: Date.now
        },
        league_type_id: {
          type: String,
          required: 'league_type',
          required:true
        }
      })

module.exports = mongoose.model('Leaguecategories', league_categories)

Tom Slabbaert · Accepted Answer · 2019-11-25 12:46:10Z

1

First i recommend you stop using callbacks wherever you can, its a bit dated and the code is much harder to read and maintain.

I re-wrote your code a little bit to look closer to what i'm used to, this does not mean this style is better, i just personally think its easier to understand what's going on.

async function fetchLeague(req, res, next) {
    try {
        //get types
        let types = await Leaguetype.find({});

        //iterate over all types.
        let results = await Promise.all(types.map(async (type) => {
            let categories = await Leaguecategories.find({"league_type_id": type._id});
            return Promise.all(categories.map(async (category) => {
                 return League.find({"league_category_id": category._id})
            }))
        }));

        // results is in the form of [ [ [ list of leagues] * per category ] * per type ]
       // if a certain category or type did not have matches it will be an empty array.
        return results;
    } catch (error) {
        console.log('no', error);
        return []
    }
}

edited Nov 25, 2019 at 12:46

answered Nov 25, 2019 at 11:04

Tom Slabbaert

22.5k10 gold badges34 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Jagveer Singh Over a year ago

Thanks for your quick answer but when i am doing console.log(types) its giving me correct result but inside Promise if I console.log(type) nothing happen. It means type._id not getting. please look into this.

Tom Slabbaert Over a year ago

This is mb, i'm using bluebird promises instead of native promises. and i just wrote it as bluebird.map, i have edited my answer to match the native js promise.

Jagveer Singh Over a year ago

thanks a lot! You saved my time. One more thing i want to know that for big application should i have to ignore callbacks function.

Ashish Modi Over a year ago

make sure that the number of records from leagueType collection aren't too many else you will be opening lots of parallel promises which might end up failing. best is to batch them if you can. something like https://www.npmjs.com/package/batch-promises

Jagveer Singh Over a year ago

@tomslabbaert if i want to make some array after league.find than how to return that particular array.

Collectives™ on Stack Overflow

Not getting result in node js, mongo db using promise in loop

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related