fix(dto): properly serialize Relationship type hints

advanced_alchemy/extensions/litestar/dto.py

@@ -32,6 +32,7 @@
     MappedColumn,
     NotExtension,
     QueryableAttribute,
+    Relationship,
     RelationshipDirection,
     RelationshipProperty,
     WriteOnlyMapped,
@@ -145,28 +146,39 @@ def _(
         model_type_hints: dict[str, FieldDefinition],
         model_name: str,
     ) -> list[DTOFieldDefinition]:
-        if not isinstance(orm_descriptor, QueryableAttribute):
+        if not isinstance(orm_descriptor, QueryableAttribute):  # pragma: no cover
             msg = f"Unexpected descriptor type for '{extension_type}': '{orm_descriptor}'"
             raise NotImplementedError(msg)
 
         elem: ElementType
-        if isinstance(orm_descriptor.property, ColumnProperty):  # pyright: ignore[reportUnknownMemberType]
-            if not isinstance(orm_descriptor.property.expression, (Column, ColumnClause, Label)):  # pyright: ignore[reportUnknownMemberType]
+        if isinstance(
+            orm_descriptor.property,  # pyright: ignore[reportUnknownMemberType]
+            ColumnProperty,  # pragma: no cover
+        ):
+            if not isinstance(
+                orm_descriptor.property.expression,  # pyright: ignore[reportUnknownMemberType]
+                (Column, ColumnClause, Label),
+            ):
                 msg = f"Expected 'Column', got: '{orm_descriptor.property.expression}, {type(orm_descriptor.property.expression)}'"  # pyright: ignore[reportUnknownMemberType]
                 raise NotImplementedError(msg)
             elem = orm_descriptor.property.expression  # pyright: ignore[reportUnknownMemberType,reportUnknownVariableType]
         elif isinstance(orm_descriptor.property, (RelationshipProperty, CompositeProperty)):  # pyright: ignore[reportUnknownMemberType,reportUnknownVariableType]
             elem = orm_descriptor.property  # pyright: ignore[reportUnknownMemberType,reportUnknownVariableType]
-        else:
+        else:  # pragma: no cover
             msg = f"Unhandled property type: '{orm_descriptor.property}'"  # pyright: ignore[reportUnknownMemberType]
             raise NotImplementedError(msg)
 
         default, default_factory = _detect_defaults(elem)
 
         try:
-            if (field_definition := model_type_hints[key]).origin in {Mapped, WriteOnlyMapped, DynamicMapped}:
+            if (field_definition := model_type_hints[key]).origin in {
+                Mapped,
+                WriteOnlyMapped,
+                DynamicMapped,
+                Relationship,
+            }:
                 (field_definition,) = field_definition.inner_types
-            else:
+            else:  # pragma: no cover
                 msg = f"Expected 'Mapped' origin, got: '{field_definition.origin}'"
                 raise NotImplementedError(msg)
         except KeyError:
@@ -201,13 +213,13 @@ def _(
         model_type_hints: dict[str, FieldDefinition],
         model_name: str,
     ) -> list[DTOFieldDefinition]:
-        if not isinstance(orm_descriptor, AssociationProxy):
+        if not isinstance(orm_descriptor, AssociationProxy):  # pragma: no cover
             msg = f"Unexpected descriptor type '{orm_descriptor}' for '{extension_type}'"
             raise NotImplementedError(msg)
 
         if (field_definition := model_type_hints[key]).origin is AssociationProxy:
             (field_definition,) = field_definition.inner_types
-        else:
+        else:  # pragma: no cover
             msg = f"Expected 'AssociationProxy' origin, got: '{field_definition.origin}'"
             raise NotImplementedError(msg)
 
@@ -299,7 +311,7 @@ def generate_field_definitions(cls, model_type: type[DeclarativeBase]) -> Genera
         # for each method name it is bound to. We only need to see it once, so track views of it here.
         seen_hybrid_descriptors: set[hybrid_property] = set()  # pyright: ignore[reportUnknownVariableType,reportMissingTypeArgument]
         skipped_descriptors: set[str] = set()
-        for composite_property in mapper.composites:
+        for composite_property in mapper.composites:  # pragma: no cover
             for attr in composite_property.attrs:
                 if isinstance(attr, (MappedColumn, Column)):
                     skipped_descriptors.add(attr.name)

tests/unit/test_extensions/test_litestar/test_dto.py

@@ -313,6 +313,51 @@ class B(Base):
     assert all(isinstance(val, module.A) for val in model.a)
 
 
+async def test_to_mapped_model_with_relationship_type_hint(
+    base: type[DeclarativeBase],
+    create_module: Callable[[str], ModuleType],
+    asgi_connection: Request[Any, Any, Any],
+) -> None:
+    """Test building a DTO with collection relationship, and parsing data."""
+
+    module = create_module(
+        """
+from __future__ import annotations
+
+from typing import Dict, List, Set, Tuple, Type, List
+
+from sqlalchemy import ForeignKey, Integer
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship, Relationship
+from typing_extensions import Annotated
+
+from advanced_alchemy.extensions.litestar.dto import SQLAlchemyDTO, SQLAlchemyDTOConfig
+
+class Base(DeclarativeBase):
+    id: Mapped[int] = mapped_column(primary_key=True)
+
+class A(Base):
+    __tablename__ = "a"
+    b_id: Mapped[int] = mapped_column(ForeignKey("b.id"))
+
+class B(Base):
+    __tablename__ = "b"
+    a: Relationship[List[A]] = relationship("A")
+
+dto_type = SQLAlchemyDTO[Annotated[B, SQLAlchemyDTOConfig()]]
+""",
+    )
+
+    model = await get_model_from_dto(
+        module.dto_type,
+        module.B,
+        asgi_connection,
+        b'{"id": 1, "a": [{"id": 2, "b_id": 1}, {"id": 3, "b_id": 1}]}',
+    )
+    assert isinstance(model, module.B)
+    assert len(model.a) == 2
+    assert all(isinstance(val, module.A) for val in model.a)
+
+
 async def test_to_mapped_model_with_scalar_relationship(
     create_module: Callable[[str], ModuleType],
     asgi_connection: Request[Any, Any, Any],