SO hasMany update demo

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  actions: {
  	addChild() {
    	this.store.createRecord('child', {
        parent: this.get('model'),
        name: this.get('newChildName')
      });
      this.set('newChildName', '');
    }
  }
});

application.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    let parent = this.store.createRecord('parent', {
      id: '1'
    });
    
    this.store.createRecord('child', {
      name: 'first child',
      parent: parent
    });
    
  	return this.store.find('parent', '1');
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
new Child: {{input value=newChildName}}
<button {{action "addChild"}}>add Child</button>
<br>
id: {{model.id}}
<br>
<hr />
<br>
{{#each model.childs as |c|}}
	Child: {{c.name}}
  <br>
{{/each}}

models.child.js

import DS from 'ember-data';

export default DS.Model.extend({
  parent: DS.belongsTo('parent'),
  name: DS.attr('string')
});

models.parent.js

import DS from 'ember-data';

export default DS.Model.extend({
  childs: DS.hasMany('child')
});

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}