fix: make sure custom fields are kept during inheritance (#415)

When a type is using a custom field, inheriting from it should not
change that field back to a `StrawberryDjangoField`

Fix #414

strawberry_django/fields/field.py

@@ -57,7 +57,7 @@
     from strawberry.relay.types import NodeIterableType
     from strawberry.types.info import Info
     from strawberry.unset import UnsetType
-    from typing_extensions import Literal
+    from typing_extensions import Literal, Self
 
     from strawberry_django.utils.typing import (
         AnnotateType,
@@ -115,6 +115,12 @@ def __init__(
         )
         super().__init__(*args, **kwargs)
 
+    def __copy__(self) -> Self:
+        new_field = super().__copy__()
+        new_field.disable_optimization = self.disable_optimization
+        new_field.store = self.store.copy()
+        return new_field
+
     @cached_property
     def _need_remove_filters_argument(self):
         if not self.base_resolver or not self.is_connection:

strawberry_django/type.py

@@ -352,6 +352,8 @@ def _process_type(
             # seeing it, just update its annotations/description/etc
             f.type_annotation = type_annotation
             f.description = description
+        elif isinstance(f, StrawberryDjangoField):
+            f = copy.copy(f)  # noqa: PLW2901
         elif (
             not isinstance(f, StrawberryDjangoField)
             and getattr(f, "base_resolver", None) is not None

tests/test_type.py

@@ -3,8 +3,10 @@
 
 import strawberry
 from django.db import models
+from strawberry.type import get_object_definition
 
 import strawberry_django
+from strawberry_django.fields.field import StrawberryDjangoField
 from strawberry_django.utils.typing import get_django_definition
 
 
@@ -109,3 +111,22 @@ class SomeModelType:
     assert store.select_related == ["other"]
     assert store.prefetch_related == ["other"]
     assert store.annotate == {"other_name": models.F("other__name")}
+
+
+def test_custom_field_kept_on_inheritance():
+    class SomeModel(models.Model):
+        foo = models.CharField(max_length=255)
+
+    class CustomField(StrawberryDjangoField): ...
+
+    @strawberry_django.type(SomeModel)
+    class SomeModelType:
+        foo: strawberry.auto = CustomField()
+
+    @strawberry_django.type(SomeModel)
+    class SomeModelSubclassType(SomeModelType): ...
+
+    for type_ in [SomeModelType, SomeModelSubclassType]:
+        object_definition = get_object_definition(type_, strict=True)
+        field = object_definition.get_field("foo")
+        assert isinstance(field, CustomField)