api-clients.json

{
  "data": {
    "id": "79931a85-9dda-42d8-8103-fea6ba4fc4af",
    "type": "client",
    "attributes": {
      "name": "GrubHub",
      "company-id": "grubhub",
      "address": "111 W Washington St, Chicago, IL 60602",
      "createdAt": "2016-01-20T18:40:46.000Z",
      "updatedAt": "2016-01-21T23:25:58.000Z"
    },
    "relationships": {
      "groups": {
        "data": [{
          "type": "group",
          "id": "821e42f3-ac94-4585-80e6-f29186e6dcdc"
        }]
      }
    }
  },
  "included": [{
    "id": "821e42f3-ac94-4585-80e6-f29186e6dcdc",
    "type": "group",
    "attributes": {
      "name": "My Test Group",
      "spec": "c195f45d-fa99-4602-bbec-3c44421110a8",
      "client": "79931a85-9dda-42d8-8103-fea6ba4fc4af",
      "createdAt": "2016-01-21T14:20:40.000Z",
      "updatedAt": "2016-01-21T14:20:40.000Z"
    }
  }]
}

client-model.js

export default DS.Model.extend({
  groups: DS.hasMany( 'group' ),

  name:    DS.attr(),
  address: DS.attr(),
});

group-model.js

export default DS.Model.extend({
  client: DS.belongsTo( 'client' ),
  spec:   DS.belongsTo( 'spec', {async: true} ),

  name: DS.attr()
});

route.js

model() {
  return this.store.findAll( 'client' ).then( clients => clients.get('firstObject') );
}

spec-model.js

export default DS.Model.extend({
  additional: DS.attr( 'raw' ),
  band:       DS.attr( 'raw' ),
  battery:    DS.attr(),
  camera:     DS.attr(),
  chipset:    DS.attr(),
  createdAt:  DS.attr( 'date' ),
  dimensions: DS.attr(),
  display:    DS.attr(),
  memory:     DS.attr(),
  name:       DS.attr(),
  network:    DS.attr( 'raw' ),
  os:         DS.attr(),
  ruggedized: DS.attr( 'boolean' ),
  storage:    DS.attr(),
  updatedAt:  DS.attr( 'date' ),
  variant:    DS.attr(),
  weight:     DS.attr(),
});

template.hbs

<p>groups {{ model.groups }}</p>  {!-- displays: <DS.PromiseManyArray:ember759> --}}
<p>group spec {{ model.groups.firstObject.spec }}</p>  {!-- displays: <DS.PromiseObject:ember760>  --}}
<p>group one name <strong>{{ model.groups.firstObject.name }}</strong></p>  {!-- displays: My Test Group --}}
<p>group spec name <strong>{{ model.groups.firstObject.spec.content }}</strong></p>  {!-- displays nothing --}}