Try to move some code into parent class

Before merge of the PR, this should be squashed into different commit.

pdc/apps/common/viewsets.py

@@ -146,6 +146,8 @@ class StrictQueryParamMixin(object):
     `query_params` class attribute on the serializer. Note that this should
     only include the parameters that are passed via URL query string, not
     request body fields.
+
+    It also provides some helper functions for examining request.
     """
     def initial(self, request, *args, **kwargs):
         super(StrictQueryParamMixin, self).initial(request, *args, **kwargs)
@@ -162,6 +164,14 @@ def initial(self, request, *args, **kwargs):
         if extra_keys:
             raise FieldError('Unknown query params: %s.' % ', '.join(sorted(extra_keys)))
 
+    def is_filtered_list(self):
+        """Return True if the current action is list and pagination is enabled.
+
+        This may be handy for adding prefetching of related models from
+        database.
+        """
+        return self.action == 'list' and self.paginator.get_page_size(self.request)
+
 
 class PDCModelViewSet(StrictQueryParamMixin,
                       ChangeSetModelMixin,

pdc/apps/release/views.py

@@ -758,7 +758,7 @@ def get_queryset(self):
         # Preloading with a separate request could be actually be slow if there
         # is no filter, so it's done only on list request with paging enabled.
         queryset = self.queryset.select_related('variant_type', 'release')
-        if self.action == 'list' and self.paginator.get_page_size(self.request):
+        if self.is_filtered_list():
             queryset = queryset.prefetch_related('variantarch_set__arch')
         return queryset