New Twiddle

adapters.application.js

import { RESTAdapter } from 'ember-data/adapter';

console.log("here")
export default RESTAdapter.extend({});

adapters.customer.js

import { RESTAdapter } from 'ember-data/adapter';

export default RESTAdapter.create({});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  async init() {
  	this.store.push({
      data: [{
        type: 'customer',
        id: 1,
  			attributes: {
  				salesforceAccount: 1,
        }
      }]
    });
    
    let customer = this.store.peekRecord('customer', 1);
    console.log(await customer.get('salesforceAccount'));
  }
});

models.customer.js

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

export default Model.extend({
  salesforceAccount: belongsTo('salesforce-account'),
});

models.salesforce-account.js

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

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

templates.application.hbs

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

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"
  }
}