js/libs/ember-data.js
function(store, record, url) {
    var id   = get(record, 'id'),
        type = record.constructor.typeKey;

    return this.ajax(this.urlPrefix(url, this.buildURL(type, id)), 'GET');
  }
function(store, record, url) {
    var id   = get(record, 'id'),
        type = record.constructor.typeKey;

    return this.ajax(this.urlPrefix(url, this.buildURL(type, id)), 'GET');
  }
Called by the store in order to fetch a JSON array for
the unloaded records in a belongs-to relationship that were originally
specified as a URL (inside of `links`).

For example, if your original payload looks like this:

```js
{
"person": {
"id": 1,
"name": "Tom Dale",
"links": { "group": "/people/1/group" }
}
}
```

This method will be called with the parent record and `/people/1/group`.

The `findBelongsTo` method will make an Ajax (HTTP GET) request to the originally specified URL.

@method findBelongsTo
@param {DS.Store} store
@param {DS.Model} record
@param {String} url
@returns {Promise} promise