Mongoose: Saving ref of another document into an array of objects document returns empty array

Question

I'm trying to add specific document's ref id into another document's array of object. So that I can use populate method. But somehow the array remains empty even after pushing the ref. Please help me. Thank you in advance.

Here is list.js:

  const mongoose = require('mongoose');

  const User = require('./user');
  const Task = require('./task');
  const Schema = mongoose.Schema;
  // User Schema
  const ListSchema = mongoose.Schema({
    item:{
      type: String,
      required: true
    },
    purpose:{
      type: String,
      required: true
    },
    user: {
      type: Schema.ObjectId,
      ref:"User"
    },
    deadline:{
      type: Date,
      default: null
    }
  });

  const List = module.exports = mongoose.model('List', ListSchema);

task.js:

  const mongoose = require('mongoose');
  const Schema = mongoose.Schema;
  const List = require('./list');
  // User Schema
  const TaskSchema = mongoose.Schema({
    task:{
      type: String,
      required: true
    },
    list: [{
      type: Schema.Types.ObjectId,
      ref:'List'
    }]

  });

  const Task = module.exports = mongoose.model('Task', TaskSchema);

Here is how I create and save new task instance:

  const express = require('express');
  const mongoose = require('mongoose');
  const router = express.Router();

  let List = require('../models/list');
  let User = require('../models/user');
  let Task = require('../models/task');

  router.post('/add', isAuthenticated, function(req,res){
    var tasker = req.body.task, listshash= [];
    var startIndex = 0, index;
      var x,y,listid= [];
      while ((index = tasker.indexOf("#", startIndex)) > -1) {
        var ind = tasker.indexOf(" ", index);
        if(ind == -1)
            listshash.push(tasker.substring(index+1));
      else  
          listshash.push(tasker.substring(index+1,ind));
          startIndex = index + 1;
      }

      //Instance of task
      var taskIns = new Task({task: req.body.task});

      List.find({user: req.session.passport.user}, function(err, lists){
      for(x in lists){
        for(y in listshash){
          if(lists[x].item.toLowerCase().replace(/\s/g,'') == listshash[y]){
            //lists[x] contains the document "list" that I want to store as 
            //ref in list property array of task
            taskIns.list.push(lists[x]);
            //console.log(taskIns.list.push(lists[x]));

          }
        }
      }
    });
    taskIns.save(function(err, doc){
        if(err) res.json(err);
        else    {
          console.log("Saved");
          res.redirect('/lists');
      }
    });
  });
  module.exports = router;

This is how the database collection of tasks look like after inserting data: See the data

Answer 1

You should have to use async npm

List.find({user: req.session.passport.user}, function(err, lists){
     async.each(lists ,function(x,callback){
          async.each(listhash, function(y,callback){
               if(x.item.toLowerCase().replace(/\s/g,'') == y){
                   taskIns.list.push(x);
               }
          });
     });


//After that you can do save the data
  taskIns.save(function(err, doc){
        if(err) res.json(err);
        else    {
          console.log("Saved");
          res.redirect('/lists');
      }
    });
  });