Inherit ModelViewSet and ReadOnlyModelViewSet from RelatedMixin

Author: Anton-Shutik

rest_framework_json_api/views.py

@@ -148,12 +148,16 @@ def get_related_instance(self):
             raise NotFound
 
 
-class ModelViewSet(AutoPrefetchMixin, PrefetchForIncludesHelperMixin, viewsets.ModelViewSet):
+class ModelViewSet(AutoPrefetchMixin,
+                   PrefetchForIncludesHelperMixin,
+                   RelatedMixin,
+                   viewsets.ModelViewSet):
     pass
 
 
 class ReadOnlyModelViewSet(AutoPrefetchMixin,
                            PrefetchForIncludesHelperMixin,
+                           RelatedMixin,
                            viewsets.ReadOnlyModelViewSet):
     pass