Avoided error when using include query parameter on related urls

This is a regression from version 4.1.0.

Author: sliverc

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
+
+* Avoided error when using `include` query parameter on related urls (a regression since 4.1.0)
+
 ## [4.1.0] - 2021-03-08
 
 ### Added

example/tests/integration/test_browsable_api.py

@@ -18,6 +18,17 @@ def test_browsable_api_with_included_serializers(single_entry, client):
     )
 
 
+def test_browsable_api_on_related_url(author, client):
+    url = reverse("author-related", kwargs={"pk": author.pk, "related_field": "bio"})
+    response = client.get(url, data={"format": "api"})
+    content = str(response.content)
+    assert response.status_code == 200
+    assert re.search(r"JSON:API includes", content)
+    assert re.search(
+        r'<input type="checkbox" name="includes" [^>]* value="metadata"', content
+    )
+
+
 def test_browsable_api_with_no_included_serializers(client):
     response = client.get(reverse("projecttype-list", kwargs={"format": "api"}))
     content = str(response.content)

example/tests/test_views.py

@@ -433,7 +433,7 @@ def test_retrieve_related_single_reverse_lookup(self):
         url = reverse(
             "author-related", kwargs={"pk": self.author.pk, "related_field": "bio"}
         )
-        resp = self.client.get(url)
+        resp = self.client.get(url, data={"include": "metadata"})
         expected = {
             "data": {
                 "type": "authorBios",
@@ -448,7 +448,14 @@ def test_retrieve_related_single_reverse_lookup(self):
                     },
                 },
                 "attributes": {"body": str(self.author.bio.body)},
-            }
+            },
+            "included": [
+                {
+                    "attributes": {"body": str(self.author.bio.metadata.body)},
+                    "id": str(self.author.bio.metadata.id),
+                    "type": "authorBioMetadata",
+                }
+            ],
         }
         self.assertEqual(resp.status_code, 200)
         self.assertEqual(resp.json(), expected)

rest_framework_json_api/renderers.py

@@ -708,7 +708,10 @@ def _get_included_serializers(cls, serializer, prefix="", already_seen=None):
 
     def get_includes_form(self, view):
         try:
-            serializer_class = view.get_serializer_class()
+            if "related_field" in view.kwargs:
+                serializer_class = view.get_related_serializer_class()
+            else:
+                serializer_class = view.get_serializer_class()
         except AttributeError:
             return
 

rest_framework_json_api/serializers.py

@@ -140,7 +140,10 @@ def validate_path(serializer_class, field_path, path):
             included_resources = get_included_resources(request)
             for included_field_name in included_resources:
                 included_field_path = included_field_name.split(".")
-                this_serializer_class = view.get_serializer_class()
+                if "related_field" in view.kwargs:
+                    this_serializer_class = view.get_related_serializer_class()
+                else:
+                    this_serializer_class = view.get_serializer_class()
                 # lets validate the current path
                 validate_path(
                     this_serializer_class, included_field_path, included_field_name