Using ember-data to populate a table - ember.js

Question

I'm relatively new to Ember CLI and have just begun to use ember-data to retrieve JSON data from my Laravel Eloquent-powered RESTful API.
I would like to populate a DataTables table with the data returned from the "Accounts" API. Each "Account" also has an embedded "Contact" record available under the "contact" key in the JSON returned from the server. The JSON is correct and an example of an "Account" record coming back from the API is:
{
"accounts": {
"id": 1,
"account_name": "My Account",
"contact": {
"id": 54,
"first_name": "John",
"last_name": "Smith"
}
}
}
In my controller I have called the serialize() method on each "Account" DS.Model in the RecordArray to convert it to a JSON object because this should allow relationships to be serialized too. However, even though I am using the ActiveModelSerializer with the EmbeddedRecordsMixin the relationships in the resulting JSON appear like this:
"contact": {
"id": "54"
}
So only the "id" field is present in the serialized, embedded "Contact" object.
My "account.js" serializer looks like this:
import DS from "ember-data";
export default DS.ActiveModelSerializer.extend(DS.EmbeddedRecordsMixin, {
attrs: {
contact: {embedded: 'always'},
},
});
and my "account.js" model looks like this:
import DS from 'ember-data';
export default DS.Model.extend({
contact: DS.belongsTo('contact', {embedded: 'always'}),
});
I cannot understand what I am doing wrong and I'd be grateful of any help anyone could offer.
Thanks.