Empty Array Outside Mongoose Function

Question

I am trying to retrieve the data from multiple collections using mongoose schema and then send the respond back in JSON format. This is the code I have written.

function GetConnections_V2(req,res){

    Connection.find({"user_id":"55006c36c30f0edc5400022d"})
     .exec(function(err,connections){

        var list = []; 
        var obj = new Object();
        connections.forEach(function(connection){
                           obj.friend_id = connection.user_id_friend;
          User.findById(connection.user_id_friend)
          .exec(function(err,user){
                    if(user !== null) {

                            obj.friend_email = user.email;
                            obj.friend_details_id = user.details;
        UserDetail.findById(user.details).exec(function (err, details) {
                                    obj.firstname = details.firstname;
                                    obj.lastname = details.lastname;
                                     obj.image = details.image;

                                list.push(obj);  
                            });
                    }
                });
            });
         });
       console.log(list);
       res.send(list);
};

Now on executing this code. It is returning empty array. How do I resolve this problem ?

you are calling `async` functions inside for loop. Use `async` lib or `promise`. — Mukesh Sharma, Jan 29 '17 at 11:41

Mukesh Sharma · Accepted Answer · 2017-01-29T11:57:29.177

You are calling async functions inside for loop. That's why list is empty.

You can use async to solve this problem.

var async = require('async');

function GetConnections_V2(req,res){

    Connection.find({"user_id":"55006c36c30f0edc5400022d"})
     .exec(function(err,connections){

        var list = []; 

        async.each(connections, function(connection, callback){
            var obj = new Object();
            obj.friend_id = connection.user_id_friend;

            User.findById(connection.user_id_friend)
                .exec(function(err,user){
                    if(user !== null) {
                        obj.friend_email = user.email;
                        obj.friend_details_id = user.details;
                        UserDetail.findById(user.details).exec(function (err, details) {
                            obj.firstname = details.firstname;
                            obj.lastname = details.lastname;
                            obj.image = details.image;

                            list.push(obj); 
                            callback();
                        });
                    } else {
                        callback();
                    }
            });
        }, function(err){
            return res.send(list);
        });
    };
}

Hope it helps you.

It works Thankyou so much. :) I am new to this. Can you please explain how async and exec function works ? — Ahsan Jamal, Jan 29 '17 at 12:02
You can read about asynchronous programming here https://blog.risingstack.com/node-hero-async-programming-in-node-js/ — Mukesh Sharma, Jan 29 '17 at 12:14

Empty Array Outside Mongoose Function

1 Answers1