how to handle nested json responses with ember?

Maybe I'm overlooking something, but I from can't figure out how I'm supposed

I have a JSON coming from the server which looks like this

{
  "articles": [
    {
      "user": {
        "name": "user",
        "username": "user",
        "_id": "52755cba74a1fbe54a000002"
      },
      "_id": "5275698c53da846e70000001",
      "__v": 0,
      "content": "content",
      "title": "title",
      "created": "2013-11-02T21:07:24.554Z"
    }
  ]
}

In the template, I'm accessing content and created fine, but when I try to get user.name, nothing comes out:

    {{#each article in model}}
        <span>{{ article.title }}</span>
        <span>by {{ article.user.name }}</span>
        <span>{{ article.created }}</span>
    {{/each}}

I noticed that in the model, whatever I don't define, won't appear in the template, so it looks like this:

title: DS.attr('string'),
content: DS.attr('string'),
created: DS.attr('date')

But when I try to add:

user: {
       name: DS.attr('string')
}

To match the nested json, I get an error.

Is ember not able to handle nested json? If it is, then how?

Thanks.