Mongoose - query to get data from multiple collections

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I want to get query of the mongoose in nodejs application as describe below out put.
user.js, comment.js and post.js are the model files I used.

user.js 

var mongoose = require('mongoose');  
var Schema = mongoose.Schema;  
var ObjectId = Schema.ObjectId;  

var userSchema = new Schema({  
        nick_name:{type:String},  
        email: {  
            type: String,  
            trim: true,  
            required: '{PATH} is required!',
            index: true,
        },     
    },{ collection: 'user'});

var User = mongoose.model('User', userSchema);
module.exports = User;

comment.js 

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = Schema.ObjectId;

var commentSchema = new Schema({  
         comment: type:String,  
         user_id:{
            type:Schema.Types.ObjectId, ref:'User'
         },  
         is_active :1
},{ collection: 'comment'});

post.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = Schema.ObjectId;

var postSchema = new Schema({
        post: type:String,
        user_id:{
           type:Schema.Types.ObjectId, ref:'User'
        },
        is_active :1
},{ collection: 'post'});

wants to get out put as follows:

{
 "nick_name":"prakash",
 "email":"prakash@mailinator.com",
 "comments":[
      {
      "comment":"this is a comment text1",
      "is_active":1,
      },
      {
      "comment":"this is a comment text2",
      "is_active":1,
      }
 ],
 "posts":[
      {
      "post":"this is a post text1",
      "is_active":1,
      },
      {
      "post":"this is a post text2",
      "is_active":1,
      },
      {
      "post":"this is a post text3",
      "is_active":1,
      },
 ]
}

dependencies

"express"  => "version": "4.7.4",
"mongoose" => "version": "4.4.5",
"mongodb"  => "version": "2.4.9",
"OS"  => "ubuntu 14.04 lts 32bit",

if query is not possible ,please suggests me a proper mongoose plugn. but I don't want to any changes in user.js file and its userSchema object.

mongoose node.js mongodb
4 Answers

It is possible .you should use aggregation. it should work. Initiate the variable

    var mongoose = require('mongoose');
    var userCollection = require('./user');//import user model file
    var resources = {
    nick_name: "$nick_name",
    email: "$email"};

    userCollection.aggregate([{
            $group: resources
        }, {
            $lookup: {
                from: "Comments", // collection to join
                localField: "_id",//field from the input documents
                foreignField: "user_id",//field from the documents of the "from" collection
                as: "comments"// output array field
            }
        }, {
            $lookup: {
                from: "Post", // from collection name
                localField: "_id",
                foreignField: "user_id",
                as: "posts"
            }
        }],function (error, data) {
         return res.json(data);
     //handle error case also
});
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