fix: favour SA mapped type over impl type (#513)

polyfactory/factories/sqlalchemy_factory.py

@@ -129,11 +129,10 @@ def get_type_from_column(cls, column: Column) -> type:
         elif issubclass(column_type, types.ARRAY):
             annotation = List[column.type.item_type.python_type]  # type: ignore[assignment,name-defined]
         else:
-            annotation = (
-                column.type.impl.python_type  # pyright: ignore[reportGeneralTypeIssues]
-                if hasattr(column.type, "impl")
-                else column.type.python_type
-            )
+            try:
+                annotation = column.type.python_type
+            except NotImplementedError:
+                annotation = column.type.impl.python_type  # type: ignore[attr-defined]
 
         if column.nullable:
             annotation = Union[annotation, None]  # type: ignore[assignment]

tests/sqlalchemy_factory/test_sqlalchemy_factory_common.py

@@ -1,6 +1,7 @@
 from dataclasses import dataclass
 from enum import Enum
-from typing import Any, Callable, Type
+from typing import Any, Callable, Type, Union
+from uuid import UUID
 
 import pytest
 from sqlalchemy import Column, ForeignKey, Integer, String, create_engine, inspect, orm, types
@@ -347,3 +348,37 @@ class ModelFactory(SQLAlchemyFactory[ModelWithAlias]):
 
     result = ModelFactory.build()
     assert isinstance(result.name, str)
+
+
+@pytest.mark.parametrize("python_type_", (UUID, None))
+def test_sqlalchemy_custom_type_from_type_decorator(python_type_: Union[type, None]) -> None:
+    class CustomType(types.TypeDecorator):
+        impl = types.CHAR(32)
+        cache_ok = True
+
+        if python_type_ is not None:
+
+            @property
+            def python_type(self) -> type:
+                return python_type_
+
+    class Base(metaclass=DeclarativeMeta):
+        __abstract__ = True
+        __allow_unmapped__ = True
+
+        registry = _registry
+        metadata = _registry.metadata
+
+    class Model(Base):
+        __tablename__ = f"model_with_custom_types_{python_type_}"
+
+        id: Any = Column(Integer(), primary_key=True)
+        custom_type: Any = Column(type_=CustomType(), nullable=False)
+
+    class ModelFactory(SQLAlchemyFactory[Model]):
+        __model__ = Model
+
+    instance = ModelFactory.build()
+
+    expected_type = python_type_ if python_type_ is not None else CustomType.impl.python_type
+    assert isinstance(instance.custom_type, expected_type)