discussion refactor error

django.request -- ERROR -- 2015-11-17 14:31:09,127: Internal Server Error: /api/private/discussion/
Traceback (most recent call last):
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/cbweb/coursebook/pathwright/apps/web_api/private/resources/discussion/views.py", line 47, in list_create_discussion_router
    return view(request, *args, **kwargs)
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 57, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/django/views/generic/base.py", line 69, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/rest_framework/views.py", line 407, in dispatch
    response = self.handle_exception(exc)
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/rest_framework/views.py", line 404, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/rest_framework/generics.py", line 269, in get
    return self.list(request, *args, **kwargs)
  File "/home/cbweb/coursebook/pathwright/apps/web_api/private/resources/discussion/views.py", line 171, in list
    self.offering, self.step, self.topic))
  File "/home/cbweb/.virtualenvs/coursebook/local/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 198, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/home/cbweb/coursebook/pathwright/apps/activity_feed/receivers/discussion.py", line 30, in recv_user_lists_discussions
    context_id=context.pk
AttributeError: 'DiscussionContextQuerySet' object has no attribute 'pk'
[17/Nov/2015 14:31:09] "GET /api/private/discussion/?page_size=15&page=1&ordering=-last_activity_time&type=question&context=course_74%2Cclass_23967 HTTP/1.0" 500 27557