New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  parent: Ember.computed(function() {
    var parent = this.get('store').createRecord('parent', {
      id: 'Edna',
      name: 'Edna'
    });
    return parent;
  })
});

controllers.parent.js

import Ember from 'ember';

export default Ember.Controller.extend({

  parents: Ember.computed(function() {
    return this.get('store').peekAll('parent');
  }),
  parent: Ember.computed.alias('model'),
  sons: Ember.computed.alias('parent.sons'),
  son: Ember.computed.alias('parent.firstSon'),

});

models.child.js

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

export default Model.extend({
  type: attr('string'),
  name: attr('string'),
  parent: belongsTo('parent', {async: false}),
  toy: belongsTo('toy', {async: false})
});

models.parent.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';
import Ember from 'ember';
 
export default Model.extend({
  name: attr('string'),
  children: hasMany('child', {async: true}),
  sons: Ember.computed.filterBy('children', 'type', 'son'),
  firstSon: Ember.computed.alias('sons.firstObject')
});

models.toy.js

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

export default Model.extend({
  type: attr('string')
});

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

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

Router.map(function() {
  this.route('parent', {path:'parent/:parent_id'});
});

export default Router;

routes.parent.js

import Ember from 'ember';

export default Ember.Route.extend({

  setupController: function(controller, model) {
    this._super(...arguments);
    var toy = this.get('store').createRecord('toy', {
      type: 'latte'
    });
    this.get('store').createRecord('child',
        {parent: model, type: 'son', toy: toy,
        name: 'Tyler'});
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{link-to "Link To Parent" "parent" parent}}
{{outlet}}

templates.parent.hbs

<h2>Family</h2>
<br>
<p> Total Parent Count {{parents.length}}</p>
<p> Parent {{parent.name}}</p>
<p> Son {{son.name}}</p>
<p> Son's toy {{son.toy.type}}</p>
<br>
 

twiddle.json

{
  "version": "0.14.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": { 
    "ember-data": "3.4.2"
  }
}