Passing async 'hasMany' relation to a component

i have an Ember model with a 'hasMany' relation which i don't want to embed, and i need to pass it asynchronously to a component that gets records from the relation. but when i call the component from emblem file (=user-answer userAnswers=userAnswers id=smth.id), i get an error like "no method 'get' for undefined". here is the code:

app/models/quiz_progress.coffee:

`import DS from "ember-data";`
`import ProgressMixin from "../mixins/progress_mixin"`
QuizProgress = DS.Model.extend ProgressMixin,
  userAnswers:            DS.hasMany 'user_answer', async: true
`export default QuizProgress;`

app/components/user-answer.coffee:

`import Ember from "ember";`

UserAnswerComponent = Ember.Component.extend
  tagName: 'div'
  classNames: ['ui', 'list']

  userAnswer: (->
    id = @get('id')
    answers = @get('userAnswers')
    answers.findBy('questionId', id).get('answers')
  ).property('id', 'userAnswers')

`export default UserAnswerComponent;`

and it works only when userAnswers is serialized as embedded. is there really no way to get rid of embedding? i want to pass ids only