Helper method in controller best practice?

1

I have 2 models: Post and Category. Post belongs to a Category and a Category has many Posts. Both models have an attribute cover wich contains a url to an image.

In my template I want to use a computed property ‘coverImage’ based on the cover of a post or if this is not present the cover image of the related category. My solution for this is the following:

post_controller.js

coverImage: function() {
    if (this.get('cover')) {
        cover = this.get('cover');
    } else if (this.get('category')) {
        cover = this.get('category').get('cover');
    } else {
        cover = 'images/categories/green_bg.png';
    }

    return 'background-image: url(' + cover + ')';
}.property(),

But to be able to access the category in my controller I have to set it up in my PostRoute:

post_route.js

setupController: function(controller, model) {
    controller.set('model', model);

    var category_id = model.get('category').get('id');
    this.store.find('category', category_id).then(function(c) {
        controller.set('category', c);
    })
},

Having to access a related category through store.find + waiting for the promise to fullfill feels not right. Am I missing out on some essential Ember logic and is there a much better way to accomplish my coverImage helper property?