HasManyReference and autotracking

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { inject as service } from '@ember/service';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';

	@service store;

	get numberOfComments() {
    return this.model.hasMany('comments').ids().length;
  }
	get comments() {
    return this.model.comments;
  }

	@action
	createComment() {
    this.store.createRecord('comment', { post: this.model });
  }
}

models.comment\.js

import Model, { belongsTo } from '@ember-data/model';

export default class extends Model {
  @belongsTo({ async: true }) post;
}

models.post\.js

import Model, { hasMany } from '@ember-data/model';

export default class extends Model {
  @hasMany({ async: false }) comments;
}

routes.application\.js

import Route from '@ember/routing/route';
import { inject as service } from '@ember/service';

export default class ApplicationRoute extends Route {
  @service store;
  
  model() {
    return this.store.createRecord('post');
  }
};

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>

<p><button type="button" {{on "click" (action this.createComment)}}>Create comment</button></p>

<p>Number of comments: {{this.numberOfComments}}</p>
<ul>
	{{#each this.comments}}
  	<li>Created a comment</li>
  {{/each}}
</ul>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.18.0"
  }
}