Mongoose Population

Syntax#

Query.populate(path, [select], [model], [match], [options])

Parameters#

Parameter	Explanation
path	<Object, String> either the path to populate or an object specifying all parameters
[select]	<Object, String> Field selection for the population query (can use `'-id'` to include everything but the `id` field)
[model]	<Model> The model you wish to use for population.If not specified, populate will look up the model by the name in the Schema’s ref field.
[match]	<Object> Conditions for the population
[options]	<Object> Options for the population query (sort, etc)

A simple mongoose populate example

.populate() in Mongoose allows you to populate a reference you have in your current collection or document with the information from that collection. The previous may sound confusing but I think an example will help clear up any confusion.

The following code creates two collections, User and Post:

var mongoose = require('mongoose'),
  Schema = mongoose.Schema

var userSchema = Schema({
  name: String,
  age: Number,
  posts: [{ type: Schema.Types.ObjectId, ref: 'Post' }]
});

var PostSchema = Schema({
  user: { type: Schema.Types.ObjectId, ref: 'User' },
  title: String,
  content: String
});

var User = mongoose.model('User', userSchema);
var Post = mongoose.model('Post', postSchema);

If we wanted to populate all of the posts for each user when we .find({}) all of the Users, we could do the following:

User
  .find({})
  .populate('posts')
  .exec(function(err, users) {
    if(err) console.log(err);
    //this will log all of the users with each of their posts 
    else console.log(users);
  })