How can I access the elements of a foreign set for a model in Django's get_context_data method?

I have a generic DetailView in Django 1.9.7, which uses my model Quiz to show a super-time-saving no-hassle view (thank you Django). However, I'm struggling to access a related foreign key set on my Quiz object (a set of QuizQuestion objects). Here's what I've got:

class QuizDetail(generic.DetailView):
model = Quiz

def get_context_data(self, **kwargs):
    context = super(QuizDetail, self).get_context_data(**kwargs)

    # Pass/fail chart
    passed_questions = self.model.quizquestion_set.objects.filter(user_is_correct=True)

    # ...

    return context

This gives me 'ReverseManyToOneDescriptor' object has no attribute 'objects'.

I'm not sure if trying to get the related objects using the _set is preferable to scooting around the long way and asking for QuizQuestion.objects.filter(...), but I'm operating on the basis that it is. Please correct me if I'm mistaken :)

self.model.quizquestion_set.filter(user_is_correct=True) gives: ''ReverseManyToOneDescriptor' object has no attribute 'filter''

passed_questions = self.model.quizquestion_set.all() gives 'ReverseManyToOneDescriptor' object has no attribute 'all'

P.S. I find it quite obvious that I am relatively new to Django - apologies for any silly mistakes.