You can use a different attribute other than id to determine child objects with Ember Data if you configure it. In my case for DVD Pila! I needed to set things up like this:

App.ApplicationSerializer = DS.RESTSerializer.extend({
  keyForRelationship: function(key, relationship) {
    return 'dvd_id';

Once the ApplicationSerializer was configured things finally started working fine inside the Handlebars template.

Might have to come up with a better way of hiding forms than with a Controller attribute. Maybe...

Party On!