controllers.application.js

filteredOwners: Ember.computed('petName', '[email protected].[]', function() {
  let petName = this.get('petName');
  let ownersArray = this.get('model').toArray();
  
  let filterPromise = Ember.RSVP.filter(ownersArray, owner => {
    return owner.get('pets').then( pets => {
      return pets.isAny('name', petName);
    });
  });

  return DS.PromiseArray.create({
    promise: filterPromise
  });
})