dynamic computed props and relationships

controllers.application.js

import Ember from 'ember';
import { defineProperty, computed } from '@ember/object';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  model: null,
  
  init() {
    this._super(...arguments);

    const relationName = 'test'; 
    
    this.set('model', this.store.createRecord('myModel'));
    
    defineProperty(this, 'testName', computed(`model.${relationName}`, function() {
      return this.model.get(`${relationName}.name`);
    }));
 
    defineProperty(this, 'testExists', computed(`model.${relationName}`, function() {
        return this.model.belongsTo(relationName).value() !== null;
    }));
  },

  actions: {
   addTest() {
     const test = this.store.createRecord('test', { name: 'asdf'});
     this.model.set('test', test);
   },
   removeTest() {
     this.model.set('test', null);
   },
  },
});

models.my-model.js

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

export default Model.extend({
  test: belongsTo('test'),
});

models.test.js

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

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

{{testName}}


<br>
<br>

it exists: {{if testExists "true" "false"}}

<br>
<br>
<button onclick={{action "addTest"}}>Add</button>
<button onclick={{action "removeTest"}}>Remove</button>

twiddle.json

{
  "version": "0.15.1",
  "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"
  }
}