one-to-many

controllers.application.js

import Ember from 'ember';

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

controllers.timeslots.js

import Ember from 'ember';

export default Ember.Controller.extend({
  store: Ember.inject.service(),
  
  actions: {
  	createTimeslot () {
      const timeslot = store.createRecord('timeslot', {});
      timeslot.save()
      	.then(t => this.transitionToRoute('timeslots'))
      ;
    }
  }
});

models.student.js

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

export default Model.extend({
  timeslot: DS.belongsTo('timeslot', {inverse: 'students'})
});

models.timeslot.js

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

export default Model.extend({
  name: attr('string', {defaultValue: () => faker.lorem.word()}),
  students: DS.hasMany('student', {inverse: 'timeslot'})
});

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('timeslots');
  this.route('students');
});

export default Router;

routes.students.js

import Ember from 'ember';

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

routes.timeslots.js

import Ember from 'ember';

export default Ember.Route.extend({
  store: Ember.inject.service(),
  
  model () {
  	return this.get('store').findAll('timeslot');
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<ul>
	<li>{{#link-to 'students'}}Students{{/link-to}}</li>
	<li>{{#link-to 'timeslots'}}Timeslots{{/link-to}}</li>
</ul>
<br>
<br>
{{outlet}}
<br>
<br>

templates.students.hbs

<h2>students</h2>

<ol>
	<li></li>
</ol>

templates.timeslots.hbs

<h2>Timeslots</h2>

<ol>
	{{#each model as |timeslot|}}
		<li>{{timslot.name}} -- {{timeslot.students.length}}</li>
  {{else}}
  	<li>No Timeslots -- add a timeslot</li>
  {{/each}}
</ol>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0",
    "faker": "https://raw.githubusercontent.com/Marak/faker.js/master/build/build/faker.min.js"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}