Object relationships in Ember with using Ember-Data

We don't use Ember-Data in our project. We got a scenario where each model has an id of another type model. In fact we don't have models as well. We are using plain Ajax.

Let's take 2 models Test and Application. A test will contain the application id to which that test is created for. When i retrieve a Test, i also want the application data. Ember-Data does this by default when we use relationships. How to achieve this with Ember-Data. There might 2 tests for same application. once an application data is retrieved, i don't want to make request again for the same application