Mongoose - query to get data from multiple collections

Question

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":"[email protected]",
 "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.

Answer 1

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
});

Answer 2

There are no 'joins' in Mongo. But what you would do is change your User Schema to store the ObjectId's of the Comment and Post documents in an array of your User. Then use 'populate' when you need the data with the user.

const userSchema = new Schema({  
    nick_name:{type:String},  
    email: {  
        type: String,  
        trim: true,  
        required: '{PATH} is required!',
        index: true,
    },
    comments: [{ type: Schema.Types.ObjectId, ref:'Comment' }],
    posts: [{ type: Schema.Types.ObjectId, ref:'Post' }]
}, {timestamps: true});

mongoose.model('User', userSchema);

Your query would then look something like this:

User.find()
    .populate('comments posts') // multiple path names in one requires mongoose >= 3.6
    .exec(function(err, usersDocuments) {
        // handle err
        // usersDocuments formatted as desired
    });

Mongoose populate docs

Answer 3

Of course it is possible, you just have to use populate, let me tell you how:

Import your schemas

var mongoose = require('mongoose');
var userSch = require('userSchema');
var postSch = require('postSchema');
var commSch = require('commentSchema');

Init all the necessary vars

var userModel = mongoose.model('User', userSch);
var postModel = mongoose.model('Post', postSch);
var commModel = mongoose.model('Comment', commSch);

And now, do the query

postModel.find({}).populate('User')
    .exec(function (error, result) {
        return callback(null, null);
    });

commModel.find({}).populate('User')
    .exec(function (error, result) {
        return callback(null, null);
    }); 

This way you get the user inside of your comment and your post, to get the post and comments inside of your user, you have to do 3 queries, one for the user, one for the comments and one for the post, and mix all together