population.js

var Mongoose = require('mongoose');
var autoIncrement = require('mongoose-auto-increment')

var Schema = Mongoose.Schema;
// Mongoose.Promise = require('bluebird');
var db = Mongoose.connect('mongodb://localhost/Population', {
  useMongoClient: true
}, (err) => {
  if (err) {
    console.log(`Can't connect to MongoDB`);
  } else {
    console.log(`Connect to MongoDb sucess`);
  }
});

autoIncrement.initialize(db);

var personSchema = Schema({
  name: String,
  age: Number,
  _id: {type: Number, ref: 'Story'} 
});

var descriptionSchema = Schema({
  content: String,
  _id: {type: Number, red: 'Story'}
});

var storySchema = Schema({
  test: Number,
  descriptionId: {type: Number, ref: 'Description'},
  personId: {type: Number, ref: 'Person'},
  title: String
});

personSchema.plugin(autoIncrement.plugin, 'Person');
storySchema.plugin(autoIncrement.plugin, 'Story');
descriptionSchema.plugin(autoIncrement.plugin, 'Description');

var Story = Mongoose.model('Story', storySchema);
var Person = Mongoose.model('Person', personSchema);
var Description = Mongoose.model('Description', descriptionSchema);

var author = new Person({
  name: 'Ian Fleming',
  age: 50
});

author.save(function (err) {
  if (err) return console.log(err);
  description = new Description({
    content: 'I hope this can be help me go sleep soon.'
  });

  description.save(function(err){
    if (err) {
      return console.log("Loi khi save story");
    }
  });
  var story1 = new Story({
    personId: author._id,
    test: 1,
    descriptionId: description._id,
    title: 'Casino Royale'
  });
  
  console.log(story1);
  story1.save(function (err) {
    if (err) {
      return console.log("Loi khi save story");
    }
    // thats it!
  });

});

Story.
  findOne({ title: `Casino Royale` }).
  populate('personId'). // only return the Persons name
  populate('descriptionId').
  exec(function (err, story) {
    if (err) return handleError(err);
    console.log(story);
    
    // console.log('The author is %s', story.author.name);
    // // prints "The author is Ian Fleming"
    
    // console.log('The authors age is %s', story.author.age);
    // prints "The authors age is null'
  })