Emberjs: Best way to handle relationships not embedded in original Json

I have a user JSON api:

{
    "id": 1,
    "name": "Leanne Graham",
    "username": "Bret",
    "email": "Sincere@april.biz",
    "address": {
      "street": "Kulas Light",
      "suite": "Apt. 556",
      "city": "Gwenborough",
      "zipcode": "92998-3874",
      "geo": {
        "lat": "-37.3159",
        "lng": "81.1496"
      }
    }
}

and a post JSON api:

{
    "userId": 1,
    "id": 1,
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  }

I have also created related models in Ember Data: app/models/user.js:

export default Model.extend({
  name: attr('string'),
  username: attr('string'),
  email: attr('string'),
  posts: hasMany('post', { async: true })
});

app/models/post.js:

export default Model.extend({
  title: attr('string'),
  body: attr('string'),
  userId: belongsTo('user')
});

My issue is, I can't access a user's posts from the user object in ember, i.e.: user.posts is empty.

What is the best way to handle this? Does Ember Data require relationships to be embedded in JSON? Or, can I call the posts separately from the store from a Component (I have a component to display all of a user's posts)?