Fix dict when validate assignment true

ninja/schema.py

@@ -42,7 +42,7 @@ def resolve_name(obj):
 
 
 class DjangoGetter:
-    __slots__ = ("_obj", "_schema_cls", "_context")
+    __slots__ = ("_obj", "_schema_cls", "_context", "__dict__")
 
     def __init__(self, obj: Any, schema_cls: Type[S], context: Any = None):
         self._obj = obj

tests/test_schema.py

@@ -4,6 +4,7 @@
 import pytest
 from django.db.models import Manager, QuerySet
 from django.db.models.fields.files import ImageFieldFile
+from pydantic_core import ValidationError
 
 from ninja import Schema
 from ninja.schema import DjangoGetter, Field
@@ -194,3 +195,23 @@ class Somechema(Schema):
 
     dg = DjangoGetter({"i": 1}, Somechema)
     assert repr(dg) == "<DjangoGetter: {'i': 1}>"
+
+
+def test_django_getter_validates_assignment():
+    class ValidateAssignmentSchema(Schema):
+        str_var: str
+
+        model_config = {"validate_assignment": True}
+
+    schema_inst = ValidateAssignmentSchema(str_var="test_value")
+
+    # Validate we can re-assign the value, this is a test for
+    # a bug where validate_assignment would cause an AttributeError
+    # for __dict__ on the target schema.
+    schema_inst.str_var = "reassigned_value"
+    try:
+        schema_inst.str_var = 5
+        raise AssertionError()
+    except ValidationError:
+        # We expect this error, all is okay
+        pass