Ember Data - hasMany / belongs with a different model than default

In Ember Data, how do you define a belongsTo / hasMany association that uses a different model or foreign key than the default one?

For example, I have App.Item

which belongs to models App.User

, but I want to access the user using an attribute owner

:

App.Item = DS.Model.extend({
  owner: DS.belongsTo('App.User'),
});

item.get('owner'); // should be an App.User

// And the data from the server looks like:
{
  owner: 2, //id
}