Flattening an array with CPs

controllers.application\.js

import Controller from '@ember/controller';
import { computed } from '@ember/object';

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

  owners = [
    {
      pets: [
        {name: 'Foo'},
   	  ],
    },
  ];

  @computed('owners.@each.pets')
  get petsArrays() {
    return this
      .owners
      .map((owner) => owner.pets);
  }

  @computed('petsArrays.@each.[]')
  get pets() {
    return this
      .petsArrays
      .map(a => a.toArray())
      .flat();
  }
      
  addPet = () => {
    this.owners[0].pets.pushObject({name: 'Bar'});
  };
}

templates.application\.hbs

<button {{on 'click' this.addPet}}>
  Add pet
</button>


<h1>each owners; each owner.pets</h1>

{{#each this.owners as |owner|}}
  {{#each owner.pets as |pet|}}
    <p>{{pet.name}}</p>
  {{/each}}
{{/each}}



<h1>each pets</h1>

{{#each this.pets as |pet|}}
  <p>{{pet.name}}</p>
{{/each}}

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"
  }
}