Deprecated support for django-polymorphic resources (#1303)

Desired for Django Polymorphic support to be added in an external
3rd party library in case there is a demand and someone is to be
found who will take the lead.

Author: sliverc

CHANGELOG.md

@@ -14,6 +14,10 @@ any parts of the framework not mentioned in the documentation should generally b
 
 * Ensured that an empty `included` array is returned in responses when the `include` query parameter is present but no related resources exist.
 
+### Deprecated
+
+* Deprecated support for using Polymorphic resources through [django-polymorphic](https://github.com/jazzband/django-polymorphic). There is currently no replacement. In case you are affected of this change please join [our discussion](https://github.com/django-json-api/django-rest-framework-json-api/discussions/1194).
+
 ## [8.0.0] - 2025-07-24
 
 ### Added

docs/usage.md

@@ -863,6 +863,17 @@ field_name_mapping = {
 
 ### Working with polymorphic resources
 
+--
+
+**Deprecation notice:**
+
+
+Support for using Polymorphic resources through [django-polymorphic](https://github.com/jazzband/django-polymorphic) is deprecated and will be removed in a future release.
+
+There is currently no replacement. In case you are affected of this change please join [our discussion](https://github.com/django-json-api/django-rest-framework-json-api/discussions/1194).
+
+---
+
 Polymorphic resources allow you to use specialized subclasses without requiring
 special endpoints to expose the specialized versions. For example, if you had a
 `Project` that could be either an `ArtProject` or a `ResearchProject`, you can

rest_framework_json_api/serializers.py

@@ -1,3 +1,4 @@
+import warnings
 from collections.abc import Mapping
 
 from django.core.exceptions import ObjectDoesNotExist
@@ -342,6 +343,16 @@ def __new__(cls, name, bases, attrs):
         if not parents:
             return new_class
 
+        warnings.warn(
+            DeprecationWarning(
+                "Support for polymorphic resources is deprecated."
+                "There is currently no replacement. In case you are affected of this "
+                "change please join discussion at "
+                "https://github.com/django-json-api/django-rest-framework-json-api/discussions/1194."
+            ),
+            stacklevel=2,
+        )
+
         polymorphic_serializers = getattr(new_class, "polymorphic_serializers", None)
         assert (
             polymorphic_serializers is not None

setup.cfg

@@ -63,6 +63,7 @@ DJANGO_SETTINGS_MODULE=example.settings.test
 filterwarnings =
     error::DeprecationWarning
     error::PendingDeprecationWarning
+    ignore:Support for polymorphic resources is deprecated
 testpaths =
     example
     tests