Return queryset with filtering applied (if filter form passes
        validation).

def get_queryset(self):
        """
        Return queryset with filtering applied (if filter form passes
        validation).
        """
        qs = super(FilterFormMixin, self).get_queryset()
        filter_form = self.get_filter()
        if filter_form.is_valid():
            qs = filter_form.filter(qs).distinct()
        return qs