http://stackoverflow.com/questions/42260246/link-to-works-in-index-hbs-but-not-in-application-hbs/42268016

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

models.category.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('cars', function(){
    this.route('category', { path: '/:category_id' });    
  });
});

export default Router;

routes.cars.category.js

import Ember from 'ember';

export default Ember.Route.extend({
  model(params){
    console.log(' params.id ',params.category_id);
    return params.category_id;
  }
});

routes.cars.js

import Ember from 'ember';

export default Ember.Route.extend({
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{#link-to "cars.category" "mini"}} Cars.Category {{/link-to}}
<br>
{{outlet}}
<br>
<br>

templates.cars.category.hbs

category-{{model}}
{{outlet}}

templates.cars.hbs

cars
{{outlet}}

twiddle.json

{
  "version": "0.11.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.2",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.10.2",
    "ember-testing": "2.10.2"
  },
  "addons": {}
}