New Twiddle

adapters.user.js

import Ember from 'ember';
import DS from 'ember-data';
export default DS.JSONAPIAdapter.extend({
	findRecord() {
    return {
      "data": {
        "type": "user",
        "relationships": {
          "roles": {
            "data": [
              {
                "type": "role",
                "id": "admin"
              },
              {
                "type": "role",
                "id": "user"
              }
            ]
          }
        },
        "id": "admin",
        "attributes": {
          "username": "admin",
          "email": "[email protected]"
        }
      }
    };
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

models.role.js

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

export default DS.Model.extend({
  name:        DS.attr('string'),
  description: DS.attr('string'),
  users:       DS.hasMany('user')
});

models.user.js

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

export default DS.Model.extend({
  username: DS.attr('string'),
  email:    DS.attr('string'),
  roles:    DS.hasMany('role', { async: true }),
});

routes.application.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    return this.store.findRecord('user', '1');
  }
});

templates.application.hbs

{{model.username}}
<br>
{{model.email}}
<br>
<ul>
{{#each model.roles as |role|}}
  <li>
  {{role.id}}
  </li>  
{{/each}}
</ul>

twiddle.json

{
  "version": "0.10.4",
  "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": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}