Merge pull request #841 from bckohan/drf_bug

Polymorphic serializer validated data is now updated with the child data

Author: bckohan

docs/changelog/index.rst

@@ -1,7 +1,12 @@
 Changelog
 =========
 
-v4.10.0 (2026-XX-XX)
+v4.10.1 (2026-01-13)
+--------------------
+
+* Fixed `Django-polymorphic does not update the PolymorphicSerializer's validated_data after running the child's validation method <https://github.com/jazzband/django-polymorphic/pull/378>`_
+
+v4.10.0 (2026-01-13)
 --------------------
 
 This release is primarily an integrations release. Many tests were added for the documented

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "django-polymorphic"
-version = "4.10.0"
+version = "4.10.1"
 description = "Seamless polymorphic inheritance for Django models."
 readme = "README.md"
 license = "BSD-3-Clause"

src/polymorphic/__init__.py

@@ -19,7 +19,7 @@
 Seamless Polymorphic Inheritance for Django Models
 """
 
-VERSION = "4.10.0"
+VERSION = "4.10.1"
 
 __title__ = "Django Polymorphic"
 __version__ = VERSION  # version synonym for backwards compatibility

src/polymorphic/contrib/drf/serializers.py

@@ -93,6 +93,10 @@ def is_valid(self, *args, **kwargs):
             child_valid = False
         else:
             child_valid = serializer.is_valid(*args, **kwargs)
+            # Update parent's validated_data with child's validated_data
+            # to preserve any modifications made in child's validate() method
+            if child_valid and hasattr(self, "_validated_data"):
+                self._validated_data.update(serializer._validated_data)
             self._errors.update(serializer.errors)
         return valid and child_valid
 

src/polymorphic/tests/examples/integrations/drf/test.py

@@ -3,6 +3,7 @@
 import pytest
 
 try:
+    from rest_framework import serializers
     from rest_framework.test import APIClient
 
     from polymorphic.contrib.drf.serializers import PolymorphicSerializer
@@ -302,6 +303,71 @@ def test_get_serializer_from_resource_type_keyerror_propagation(self):
         assert "resourcetype" in excinfo.value.detail
         assert "Invalid resourcetype" in str(excinfo.value.detail["resourcetype"])
 
+    def test_validate_method_modifications_are_preserved(self):
+        """Test that modifications made in child serializer's validate() method are preserved."""
+        # Track whether the extra_field was present during create
+        created_with_extra_field = []
+
+        # Create a custom serializer that adds a field in validate()
+        class CustomBlogOneSerializer(BlogOneSerializer):
+            extra_field = serializers.CharField(required=False, allow_null=True)
+
+            class Meta(BlogOneSerializer.Meta):
+                fields = BlogOneSerializer.Meta.fields + ("extra_field",)
+
+            def validate(self, attrs):
+                attrs = super().validate(attrs)
+                # Simulate adding data in validate(), like adding the current user
+                attrs["extra_field"] = "added_in_validate"
+                return attrs
+
+            def create(self, validated_data):
+                # Record whether extra_field was in validated_data
+                created_with_extra_field.append("extra_field" in validated_data)
+                # Remove extra_field before creating the model instance
+                validated_data.pop("extra_field", None)
+                return super().create(validated_data)
+
+        class CustomBlogPolymorphicSerializer(PolymorphicSerializer):
+            model_serializer_mapping = {
+                BlogBase: BlogBaseSerializer,
+                BlogOne: CustomBlogOneSerializer,
+            }
+
+        # Create data without the extra_field
+        data = {
+            "name": "test",
+            "slug": "test-slug",
+            "info": "test-info",
+            "resourcetype": "BlogOne",
+        }
+
+        serializer = CustomBlogPolymorphicSerializer(data=data)
+        assert serializer.is_valid(), f"Validation errors: {serializer.errors}"
+
+        # Verify that the extra_field added in validate() is in validated_data
+        assert "extra_field" in serializer.validated_data
+        assert serializer.validated_data["extra_field"] == "added_in_validate"
+
+        # Verify that resource_type field is still preserved in parent's validated_data
+        assert "resourcetype" in serializer.validated_data
+        assert serializer.validated_data["resourcetype"] == "BlogOne"
+
+        # Save and verify that the field was present during create
+        # Note: This would fail before the fix because the parent's _validated_data
+        # wasn't updated with the child's _validated_data after calling child.is_valid()
+        instance = serializer.save()
+
+        # Verify that extra_field was indeed present when create() was called
+        assert created_with_extra_field == [True], (
+            "extra_field should have been in validated_data when create() was called"
+        )
+
+        # Verify the instance was created successfully
+        assert instance.name == "test"
+        assert instance.slug == "test-slug"
+        assert instance.info == "test-info"
+
 
 class TestProjectViewSet:
     """Test the example Project ViewSet with polymorphic serializers."""