Ember.js 2, transitionTo using multiple synamic segments in first level route

I'm using Ember >= 2.13.x.

I need to use transitionTo from a route action to go in another route.

Here is the demo ember-twiddle: http://ift.tt/2uBQU1r

I have this situation:

router.json:

Router.map(function() {
  this.route('home', {path: '/'});
  this.route('categories', {path: 'categories'});
  this.route('category', {path: ':category_id'});
  this.route('posts', {path: 'posts'});
  this.route('post', {path: ':category_id/:post_id'}); //I have multiple synamic segments in here
});

routes/application.js:

actions: {
    goToPost() {
        let post = this.store.findRecord('post', 1);
        this.transitionTo('post', post);
    }
}

routes/post.js:

model(params) {
    return this.store.findRecord('post', params.id);
},

serialize(model) {
    console.log('model in serialize():', model);
    return { category_id: model.get('category.id'), post_id: model.id };
}

templates/application.hbs:

<button type="button" >GoToPost with action (transitionTo)</button>

So when I click everything works as expected.

I fetch the model in application action and then I use this.transitionTo('post', post);.

In my post route then I have serialize() which, I read now, is using for URL composition when dynamic segments are present.

My question: I'm using it the right way?

Why I cannot use something like this: this.transitionTo('post', post.category.id, post.id); and let model() in post route fetch the model (from DB or store)?

I also tried to use this.transitionTo('post', {category_id: post.category.id, post_id: post.id}); but obviously the post route model() doesn't load anything because it really thinks the object is already there.

So, I can fix this problem with serialize() method only. Is it the right way?