Allow get_serializer_class to be overwritten for related urls without defining serializer_class fallback

CHANGELOG.md

@@ -14,6 +14,10 @@ any parts of the framework not mentioned in the documentation should generally b
 
 * Added support for Django 3.2.
 
+### Fixed
+
+* Allow `get_serializer_class` to be overwritten when using related urls without defining `serializer_class` fallback
+
 ## [4.1.0] - 2021-03-08
 
 ### Added

example/tests/test_views.py

@@ -417,12 +417,11 @@ def test_get_related_serializer_class_many(self):
     def test_get_serializer_comes_from_included_serializers(self):
         kwargs = {"pk": self.author.id, "related_field": "type"}
         view = self._get_view(kwargs)
-        related_serializers = view.serializer_class.related_serializers
-        delattr(view.serializer_class, "related_serializers")
+        related_serializers = view.get_serializer_class().related_serializers
+        delattr(view.get_serializer_class(), "related_serializers")
         got = view.get_related_serializer_class()
         self.assertEqual(got, AuthorTypeSerializer)
-
-        view.serializer_class.related_serializers = related_serializers
+        view.get_serializer_class().related_serializers = related_serializers
 
     def test_get_related_serializer_class_raises_error(self):
         kwargs = {"pk": self.author.id, "related_field": "unknown"}

example/views.py

@@ -208,17 +208,15 @@ class NoFiltersetEntryViewSet(EntryViewSet):
 
 class AuthorViewSet(ModelViewSet):
     queryset = Author.objects.all()
-    serializer_classes = {
-        "list": AuthorListSerializer,
-        "retrieve": AuthorDetailSerializer,
-    }
-    serializer_class = AuthorSerializer  # fallback
 
     def get_serializer_class(self):
-        try:
-            return self.serializer_classes.get(self.action, self.serializer_class)
-        except AttributeError:
-            return self.serializer_class
+        serializer_classes = {
+            "list": AuthorListSerializer,
+            "retrieve": AuthorDetailSerializer,
+        }
+
+        action = getattr(self, "action", "")
+        return serializer_classes.get(action, AuthorSerializer)
 
 
 class CommentViewSet(ModelViewSet):

rest_framework_json_api/views.py

@@ -154,7 +154,7 @@ def get_related_serializer(self, instance, **kwargs):
         return serializer_class(instance, **kwargs)
 
     def get_related_serializer_class(self):
-        parent_serializer_class = super(RelatedMixin, self).get_serializer_class()
+        parent_serializer_class = self.get_serializer_class()
 
         if "related_field" in self.kwargs:
             field_name = self.kwargs["related_field"]