Allow users to overwrite get_serializer_class while using related urls (#860)

* This attempt to fix the issues breaks tests

An attempt to fix #859, which unfortunately breaks two tests in test_views.

* Removed misleading comment

Tha basic method was copied over from the GenericAPIView. The comment here does not fit, though.

* bein more explicit about the changes

* Use correct serializer for rendering

Ensure that the correct resource is returned during rendering, which in turn requires to use the correct serializer, depending on if it is a related resource or the parent resource.
sliverc pointed out the issue here.

* Add provision for tests

* Describe the fix.

* Fixed failing tests

As pointed out by n2ygk, the schema names here must reflect the Serializer class names, which I changed in the two affected test cases.

* Update CHANGELOG.md

Clarified changelog entry

* Fixed linting issues

Co-authored-by: Ulrich Schuster <[email protected]>
Co-authored-by: Oliver Sauder <[email protected]>

Author: uliSchuster

AUTHORS

@@ -33,4 +33,5 @@ Sergey Kolomenkin <https://kolomenkin.com>
 Stas S. <[email protected]>
 Tim Selman <[email protected]>
 Tom Glowka <[email protected]>
+Ulrich Schuster <[email protected]>
 Yaniv Peer <[email protected]>

CHANGELOG.md

@@ -14,6 +14,10 @@ any parts of the framework not mentioned in the documentation should generally b
 
 * Ability for the user to select `included_serializers` to apply when using `BrowsableAPI`, based on available `included_serializers` defined for the current endpoint.
 
+### Fixed
+
+* Allow users to overwrite a view's `get_serializer_class()` method when using [related urls](https://django-rest-framework-json-api.readthedocs.io/en/stable/usage.html#related-urls)
+
 
 ## [4.0.0] - 2020-10-31
 

example/serializers.py

@@ -261,6 +261,14 @@ def get_first_entry(self, obj):
         return obj.entries.first()
 
 
+class AuthorListSerializer(AuthorSerializer):
+    pass
+
+
+class AuthorDetailSerializer(AuthorSerializer):
+    pass
+
+
 class WriterSerializer(serializers.ModelSerializer):
     included_serializers = {
         'bio': AuthorBioSerializer

example/tests/snapshots/snap_test_openapi.py

@@ -65,7 +65,7 @@
             "properties": {
               "data": {
                 "items": {
-                  "$ref": "#/components/schemas/Author"
+                  "$ref": "#/components/schemas/AuthorList"
                 },
                 "type": "array"
               },
@@ -171,7 +171,7 @@
           "schema": {
             "properties": {
               "data": {
-                "$ref": "#/components/schemas/Author"
+                "$ref": "#/components/schemas/AuthorDetail"
               },
               "included": {
                 "items": {

example/tests/test_views.py

@@ -367,32 +367,32 @@ def test_get_related_instance_model_field(self):
         got = view.get_related_instance()
         self.assertEqual(got, self.author.id)
 
-    def test_get_serializer_class(self):
+    def test_get_related_serializer_class(self):
         kwargs = {'pk': self.author.id, 'related_field': 'bio'}
         view = self._get_view(kwargs)
-        got = view.get_serializer_class()
+        got = view.get_related_serializer_class()
         self.assertEqual(got, AuthorBioSerializer)
 
-    def test_get_serializer_class_many(self):
+    def test_get_related_serializer_class_many(self):
         kwargs = {'pk': self.author.id, 'related_field': 'entries'}
         view = self._get_view(kwargs)
-        got = view.get_serializer_class()
+        got = view.get_related_serializer_class()
         self.assertEqual(got, EntrySerializer)
 
     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')
-        got = view.get_serializer_class()
+        got = view.get_related_serializer_class()
         self.assertEqual(got, AuthorTypeSerializer)
 
         view.serializer_class.related_serializers = related_serializers
 
-    def test_get_serializer_class_raises_error(self):
+    def test_get_related_serializer_class_raises_error(self):
         kwargs = {'pk': self.author.id, 'related_field': 'unknown'}
         view = self._get_view(kwargs)
-        self.assertRaises(NotFound, view.get_serializer_class)
+        self.assertRaises(NotFound, view.get_related_serializer_class)
 
     def test_retrieve_related_single_reverse_lookup(self):
         url = reverse('author-related', kwargs={'pk': self.author.pk, 'related_field': 'bio'})

example/views.py

@@ -15,6 +15,8 @@
 
 from example.models import Author, Blog, Comment, Company, Entry, Project, ProjectType
 from example.serializers import (
+    AuthorDetailSerializer,
+    AuthorListSerializer,
     AuthorSerializer,
     BlogDRFSerializer,
     BlogSerializer,
@@ -185,7 +187,16 @@ class NoFiltersetEntryViewSet(EntryViewSet):
 
 class AuthorViewSet(ModelViewSet):
     queryset = Author.objects.all()
-    serializer_class = AuthorSerializer
+    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
 
 
 class CommentViewSet(ModelViewSet):

rest_framework_json_api/utils.py

@@ -52,7 +52,10 @@ def get_resource_name(context, expand_polymorphic_types=False):
         resource_name = getattr(view, 'resource_name')
     except AttributeError:
         try:
-            serializer = view.get_serializer_class()
+            if 'kwargs' in context and 'related_field' in context['kwargs']:
+                serializer = view.get_related_serializer_class()
+            else:
+                serializer = view.get_serializer_class()
             if expand_polymorphic_types and issubclass(serializer, PolymorphicModelSerializer):
                 return serializer.get_polymorphic_types()
             else:

rest_framework_json_api/views.py

@@ -144,10 +144,15 @@ def retrieve_related(self, request, *args, **kwargs):
         if isinstance(instance, Iterable):
             serializer_kwargs['many'] = True
 
-        serializer = self.get_serializer(instance, **serializer_kwargs)
+        serializer = self.get_related_serializer(instance, **serializer_kwargs)
         return Response(serializer.data)
 
-    def get_serializer_class(self):
+    def get_related_serializer(self, instance, **kwargs):
+        serializer_class = self.get_related_serializer_class()
+        kwargs.setdefault('context', self.get_serializer_context())
+        return serializer_class(instance, **kwargs)
+
+    def get_related_serializer_class(self):
         parent_serializer_class = super(RelatedMixin, self).get_serializer_class()
 
         if 'related_field' in self.kwargs:
@@ -179,7 +184,8 @@ def get_related_field_name(self):
 
     def get_related_instance(self):
         parent_obj = self.get_object()
-        parent_serializer = self.serializer_class(parent_obj)
+        parent_serializer_class = self.get_serializer_class()
+        parent_serializer = parent_serializer_class(parent_obj)
         field_name = self.get_related_field_name()
         field = parent_serializer.fields.get(field_name, None)