server2.js

const express = require('express');
const mongoose = require('mongoose');
const autoIncrement = require('mongoose-auto-increment');
const app = express();

mongoose.connect('mongodb://localhost/test');

var Schema = mongoose.Schema;

var personSchema = Schema({
  name: String,
  age: Number
});

var storySchema = Schema({
  title: String,
  author: Number
});

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

var Story = mongoose.model('Story', storySchema);
var Person = mongoose.model('Person', personSchema);

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

author.save(function (err) {
  if (err) return handleError(err);
  
  var story1 = new Story({
    title: 'Casino Royale',
    author: author._id    // assign the _id from the person
  });
  
  story1.save(function (err) {
    if (err) return handleError(err);
    // thats it!
  });
});


app.get('./', function(req, res) {
  Story.findOne({title: 'Casino Royale'}, function(err, story) {
    if(err) return console.log(err);
    Person.findOne({_id: story._id}, function(err, person) {
      if(err) return console.log(err);
      person.stories = story
      res.json();
    });
  });
});

app.listen(3001, ()=> console.log('server listen at 3001'));