Ember Data HasRelationship

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  store: Ember.inject.service('store'),
  init(){
  this._super(...arguments); 
    const stuff = this.get('store').createRecord('model-a');
    this.set('numberOfRelationships', stuff.get('cars.length'));
}
});

models.car.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
});

models.model-a.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  cars: hasMany('car', {async:true})
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
Number of relationships
<br>
{{numberOfRelationships}}
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "1.13.15",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}