New Twiddle

controllers.application.js

import Ember from 'ember';
import DS from 'ember-data';

function delayedResolveWith(obj) {
  return new Ember.RSVP.Promise(function(resolve, reject) {
    window.setTimeout(resolve.bind(null, obj), 1000);
  });
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  items: null,
  
  init() {
    this._super(...arguments);
    
    Ember.set(this, 'items', [{
      nested : DS.PromiseObject.create({ 
        promise: delayedResolveWith({ id: '123' })
      }),
      nestedId: Ember.computed.reads('nested.id')
    }, {
      nested : DS.PromiseObject.create({ 
        promise: delayedResolveWith({ id: '234' })
      }),
      nestedId: Ember.computed.reads('nested.id')
    }, {
      nested : DS.PromiseObject.create({ 
        promise: delayedResolveWith({ id: '345' })
      })
    }]);
  },
  
  itemsWithNestedId: Ember.computed('items.@each.nested', function() {
    return Ember.get(this, 'items').map((item) => {
      return { 
        nested: Ember.get(item, 'nested'),
        nestedId: Ember.computed.reads('nested.id')
      };
    });
  }),
  
  allIds: Ember.computed('itemsWithNestedId.@each.nestedId', function() {
    return Ember.get(this, 'itemsWithNestedId').mapBy('nestedId').join(', ');
  })
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

<div>
  <strong>items:</strong>
  <ul>
    {{#each items as |item|}}
      <li>{{item.nested.id}}</li>
    {{/each}}
  </ul>
</div>

<div>
	<strong>all item ids:</strong> {{allIds}}
</div>

<br>
<br>

twiddle.json

{
  "version": "0.8.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}