feat: add get_field_by_attr fixtures helper (#245)

src/fastapi_toolsets/fixtures/__init__.py

@@ -2,12 +2,18 @@
 
 from .enum import LoadStrategy
 from .registry import Context, FixtureRegistry
-from .utils import get_obj_by_attr, load_fixtures, load_fixtures_by_context
+from .utils import (
+    get_field_by_attr,
+    get_obj_by_attr,
+    load_fixtures,
+    load_fixtures_by_context,
+)
 
 __all__ = [
     "Context",
     "FixtureRegistry",
     "LoadStrategy",
+    "get_field_by_attr",
     "get_obj_by_attr",
     "load_fixtures",
     "load_fixtures_by_context",

src/fastapi_toolsets/fixtures/utils.py

@@ -250,6 +250,31 @@ def get_obj_by_attr(
         ) from None
 
 
+def get_field_by_attr(
+    fixtures: Callable[[], Sequence[ModelType]],
+    attr_name: str,
+    value: Any,
+    *,
+    field: str = "id",
+) -> Any:
+    """Get a single field value from a fixture object matched by an attribute.
+
+    Args:
+        fixtures: A fixture function registered via ``@registry.register``
+            that returns a sequence of SQLAlchemy model instances.
+        attr_name: Name of the attribute to match against.
+        value: Value to match.
+        field: Attribute name to return from the matched object (default: ``"id"``).
+
+    Returns:
+        The value of ``field`` on the first matching model instance.
+
+    Raises:
+        StopIteration: If no matching object is found in the fixture group.
+    """
+    return getattr(get_obj_by_attr(fixtures, attr_name, value), field)
+
+
 async def load_fixtures(
     session: AsyncSession,
     registry: FixtureRegistry,

tests/test_fixtures.py

@@ -10,6 +10,7 @@ from fastapi_toolsets.fixtures import (
     Context,
     FixtureRegistry,
     LoadStrategy,
+    get_field_by_attr,
     get_obj_by_attr,
     load_fixtures,
     load_fixtures_by_context,
@@ -951,6 +952,41 @@ class TestGetObjByAttr:
             get_obj_by_attr(self.roles, "id", "not-a-uuid")
 
 
+class TestGetFieldByAttr:
+    """Tests for get_field_by_attr helper function."""
+
+    def setup_method(self):
+        self.registry = FixtureRegistry()
+        self.role_id_1 = uuid.uuid4()
+        self.role_id_2 = uuid.uuid4()
+        role_id_1 = self.role_id_1
+        role_id_2 = self.role_id_2
+
+        @self.registry.register
+        def roles() -> list[Role]:
+            return [
+                Role(id=role_id_1, name="admin"),
+                Role(id=role_id_2, name="user"),
+            ]
+
+        self.roles = roles
+
+    def test_returns_id_by_default(self):
+        """Returns the id field when no field is specified."""
+        result = get_field_by_attr(self.roles, "name", "admin")
+        assert result == self.role_id_1
+
+    def test_returns_specified_field(self):
+        """Returns the requested field instead of id."""
+        result = get_field_by_attr(self.roles, "id", self.role_id_2, field="name")
+        assert result == "user"
+
+    def test_no_match_raises_stop_iteration(self):
+        """Propagates StopIteration from get_obj_by_attr when no match found."""
+        with pytest.raises(StopIteration, match="No object with name=missing"):
+            get_field_by_attr(self.roles, "name", "missing")
+
+
 class TestGetPrimaryKey:
     """Unit tests for the _get_primary_key helper (composite PK paths)."""