def METHOD_NAME(self, request):
    """ delete a notification by username
    Permission checking:
    1. login user.
    """
    username = request.user.username
    UserNotification.objects.remove_user_notifications(username)
    cache_key = get_cache_key_of_unseen_notifications(username)
    cache.METHOD_NAME(cache_key)
    return Response({'success': True})