Django-polymorphic does not update the PolymorphicSerializer's validated_data after running the child's validation method

[johnmatthewtennant]

I override the self.validate() method in a polymorphic model. In that method, I make some changes to validated data, namely adding the user.

validated_data['user'] = self.context['request'].user

I noticed this change wasn't being reflected in the created object.
This is because the PolymorphicSerializer does not update its _validated_data after running the child's validate method.

The problematic code is in the "is_valid" method. See my three commented lines at the bottom that could help.

    def is_valid(self, *args, **kwargs):
        valid = super(PolymorphicSerializer, self).is_valid(*args, **kwargs)
        try:
            resource_type = self._get_resource_type_from_mapping(self.validated_data)
            serializer = self._get_serializer_from_resource_type(resource_type)
        except serializers.ValidationError:
            child_valid = False
        else:
            child_valid = serializer.is_valid(*args, **kwargs)
            # resource_type = self._validated_data[self.resource_type_field_name]
            # self._validated_data = serializer._validated_data
            # self._validated_data[self.resource_type_field_name] = resource_type
            self._errors.update(serializer.errors)
        return valid and child_valid 

My workaround has been to override the perform_create() method on the ViewSet as follows:

    def perform_create(self, serializer):
        child_resource_type = serializer.validated_data[serializer.resource_type_field_name]
        child_serializer = serializer._get_serializer_from_resource_type(child_resource_type)
        serializer.instance = child_serializer.save()