Fcoder Fcoder - 4 months ago 10x
Javascript Question

fetching data from other collections inside Mongoose find method

I'm working on a App with Node.js and mongoose(mongodb). Is there any way to fetch information from other collections inside find method except

model population
works with
and my id's in the other collection cant be duplicate and i cant have one to many relation.

For example every user has more than one books. in the books schema
's should be duplicate and a bunch of them has the same user id. But i don't want this. i want to compare other field.

I read
in Mongoose documentation but i can't understand:

i can't believe for this simple need, Mongoose doesn't have a good api.

this is my schema's:

var mongoose = require('mongoose');
var Users = require('../users');
var schema = new mongoose.Schema({
book_name: String,
book_publisher: String
var book = mongoose.model('book', schema);
module.exports = book;


var mongoose = require('mongoose');
var Book = require('../book');
var Schema = mongoose.Schema;
var schema = new mongoose.Schema({
user_name: String,
books: [{ type: Schema.Types.ObjectId, ref: 'Book' }]
var users = mongoose.model('users', schema);
module.exports = users;


Essentially, the problem is not with mongoose but mongo. What you're trying to do is basically pull relational data in a non-relational database. From experience I suggest not doing this. If you can't avoid it, use postgres. Postgres supports json data.

In mongoose you can load first level relations (users -> posts) using the .populate method. If you want to pull in a second level relation (users -> posts -> replies), then you end up needing to manually create joins in code. So if a user has multiple books, you can setup your schemas like this.

   User = new mongoose.Schema({
     //existing user properties
     owned_books: [{type: mongoose.Schema.Types.ObjectId, ref: 'book'}]

    //now you can query users and populate their books by doing

Edit: It could go the other way around, where the book has a collection of users. In any case, _id needs to be unique in a table, but as a field of another document it does not need to be unique, unless you've put an index on that field.