fix: normalize batch insert rows to prevent silent data loss for nullable columns (#192)

tests/test_fixtures.py

@@ -14,10 +14,9 @@ from fastapi_toolsets.fixtures import (
     load_fixtures,
     load_fixtures_by_context,
 )
-
 from fastapi_toolsets.fixtures.utils import _get_primary_key, _instance_to_dict
 
-from .conftest import IntRole, Permission, Role, RoleCrud, User, UserCrud
+from .conftest import IntRole, Permission, Role, RoleCreate, RoleCrud, User, UserCrud
 
 
 class AppContext(str, Enum):
@@ -621,6 +620,52 @@ class TestLoadFixtures:
         count = await RoleCrud.count(db_session)
         assert count == 1
 
+    @pytest.mark.anyio
+    async def test_merge_does_not_overwrite_omitted_nullable_columns(
+        self, db_session: AsyncSession
+    ):
+        """MERGE must not clear nullable columns that the fixture didn't set.
+
+        When a fixture omits a nullable column (e.g. role_id or notes), a re-merge
+        must leave the existing DB value untouched — not overwrite it with NULL.
+        """
+        registry = FixtureRegistry()
+        admin = await RoleCrud.create(db_session, RoleCreate(name="admin"))
+        uid = uuid.uuid4()
+
+        # First load: user has role_id and notes set
+        @registry.register
+        def users():
+            return [
+                User(
+                    id=uid,
+                    username="alice",
+                    email="a@test.com",
+                    role_id=admin.id,
+                    notes="original",
+                )
+            ]
+
+        await load_fixtures(db_session, registry, "users", strategy=LoadStrategy.MERGE)
+
+        # Second load: fixture omits role_id and notes
+        registry2 = FixtureRegistry()
+
+        @registry2.register
+        def users():  # noqa: F811
+            return [User(id=uid, username="alice-updated", email="a@test.com")]
+
+        await load_fixtures(db_session, registry2, "users", strategy=LoadStrategy.MERGE)
+
+        from sqlalchemy import select
+
+        row = (
+            await db_session.execute(select(User).where(User.id == uid))
+        ).scalar_one()
+        assert row.username == "alice-updated"  # updated column changed
+        assert row.role_id == admin.id  # omitted → preserved
+        assert row.notes == "original"  # omitted → preserved
+
     @pytest.mark.anyio
     async def test_load_with_skip_existing_strategy(self, db_session: AsyncSession):
         """Load fixtures with SKIP_EXISTING strategy."""
@@ -973,6 +1018,69 @@ class TestInstanceToDict:
         assert "role_id" in d
         assert d["role_id"] is None
 
+    def test_nullable_str_no_default_omitted_not_in_dict(self):
+        """Mapped[str | None] with no default, not provided in constructor, is absent from dict."""
+        instance = User(id=uuid.uuid4(), username="u", email="e@e.com")
+        d = _instance_to_dict(instance)
+        assert "notes" not in d
+
+    def test_nullable_str_no_default_explicit_none_included(self):
+        """Mapped[str | None] with no default, explicitly set to None, is included as NULL."""
+        instance = User(id=uuid.uuid4(), username="u", email="e@e.com", notes=None)
+        d = _instance_to_dict(instance)
+        assert "notes" in d
+        assert d["notes"] is None
+
+    def test_nullable_str_no_default_with_value_included(self):
+        """Mapped[str | None] with no default and a value set is included normally."""
+        instance = User(id=uuid.uuid4(), username="u", email="e@e.com", notes="hello")
+        d = _instance_to_dict(instance)
+        assert d["notes"] == "hello"
+
+    @pytest.mark.anyio
+    async def test_nullable_str_no_default_insert_roundtrip(
+        self, db_session: AsyncSession
+    ):
+        """Fixture loading works for models with Mapped[str | None] (no default).
+
+        Both the omitted-value (→ NULL) and explicit-None paths must insert without error.
+        """
+        registry = FixtureRegistry()
+
+        uid_a = uuid.uuid4()
+        uid_b = uuid.uuid4()
+        uid_c = uuid.uuid4()
+
+        @registry.register
+        def users():
+            return [
+                User(
+                    id=uid_a, username="no_notes", email="a@test.com"
+                ),  # notes omitted
+                User(
+                    id=uid_b, username="null_notes", email="b@test.com", notes=None
+                ),  # explicit None
+                User(
+                    id=uid_c, username="has_notes", email="c@test.com", notes="hi"
+                ),  # value set
+            ]
+
+        result = await load_fixtures(db_session, registry, "users")
+
+        from sqlalchemy import select
+
+        rows = (
+            (await db_session.execute(select(User).order_by(User.username)))
+            .scalars()
+            .all()
+        )
+        by_username = {r.username: r for r in rows}
+
+        assert by_username["no_notes"].notes is None
+        assert by_username["null_notes"].notes is None
+        assert by_username["has_notes"].notes == "hi"
+        assert len(result["users"]) == 3
+
 
 class TestBatchMergeNonPkColumns:
     """Batch MERGE on a model with no non-PK columns (PK-only table)."""