"Server-side Development with NodeJS" Course -- Mongoose concurrent insert of sub-document test

insert.mongo

> db.dishes.create({
...        _id: ObjectId("56eedb8b839b02cc2b7954d5"),
...         name: 'Uthapizza',
...         description: 'Test',
...         comments: [
...             {
...                 rating: 3,
...                 comment: 'This is insane',
...                 author: 'Matt Daemon'
...             }
...         ]
...     })

server-4.js

var mongoose = require('mongoose'),
    assert = require('assert');

var Dishes = require('./models/dishes-3');

// Connection URL
var url = 'mongodb://localhost:27017/conFusion';mongoose.connect(url);
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
    // we're connected!
    console.log("Connected correctly to server");

    var id = mongoose.mongo.ObjectId("56eedb8b839b02cc2b7954d5");

    // get all the dishes
        Dishes.findByIdAndUpdate(id, {
                $set: {
                    description: 'Updated Test'
                }
            }, {
                new: true
            })
            .exec(function (err, dish) {
                setTimeout(function () {
                    if (err) throw err;
                    console.log('Updated Dish!');
                    console.log(dish);

                    dish.comments.push({
                        rating: 5,
                        comment: 'I\'m getting a sinking feeling!',
                        author: 'Leonardo di Carpaccio'
                    });

                    dish.save(function (err, dish) {
                        console.log('Updated Comments!');
                        console.log(err);
                        console.log(dish);

                        db.close();
                });
            }, 3000);
    });
});