ObjectAt(0) doesn't work with Ember.Controller

I'm trying to upgrade my Ember application to the latest Ember 1.13.2 and therefore am trying to replace all Ember.ArrayController with Ember.Controller.

I've got a problem with the category-controller of my blog. The data retrieved from my server looks like this:

 "posts": [
    {
      "category": {
         "id": "1",
         "name": "tech"}
      "title": "my title",
      "body": "post-content",
      "isPublished": true,
    },
   ...
   ]

In my category-controller I need both, the category-id and the category-name.

With the Ember.ArrayController I used objectAt(0) to get both from the first post loaded in the model for that purpose but this doesn't work with Ember.Controller anymore.

How can I get these two attributes in my controller?

This code doesn't work anymore:

  breadCrumb: function(){
    return this.objectAt(0).get('category').get('name');
  }.property('model.[]'),

  categoryId: function(){
    return this.objectAt(0).get('category').get('id');
  }.property('model.[]'),