queryParam map to different controller property

controllers.application.js

import Ember from 'ember';

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

controllers.checkout.index.js

import Ember from 'ember';

export default Ember.Controller.extend({
  bookingValid() { return false }
});

controllers.checkout.js

import Ember from 'ember';

export default Ember.Controller.extend({
  queryParams: ['quantity'],
  quantity: 1
});

controllers.checkout.payment.js

import Ember from 'ember';

export default Ember.Controller.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('checkout', function() {
    this.route('payment')
  })
});

export default Router;

routes.checkout.index.js

import Ember from 'ember';

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

routes.checkout.js

import Ember from 'ember';

export default Ember.Route.extend({
  queryParams: {
    quantity: {
      as: 'qty'
    }
  },
});

routes.checkout.payment.js

import Ember from 'ember';

export default Ember.Route.extend({
	beforeModel() {
    this._super(...arguments);
    let indexCtrl = this.controllerFor('checkout.index');
    if (!indexCtrl.bookingValid()) {
      this.replaceWith('checkout.index');
    }
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{link-to "Click me" "checkout.payment" (query-params quantity=2)}}
{{outlet}}
<br>
<br>

templates.checkout.hbs

checkout {{qty}}

<p>
	{{outlet}}
</p>

templates.checkout.index.hbs

checkout index <br>

templates.checkout.payment.hbs

checkout payment <br>

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": "2.8.3",
    "ember-template-compiler": "2.8.3"
  },
  "addons": {}
}