fix: DTO factory narrowed with a generic alias.

This PR is an attempt at handling DTOs that are narrowed with a `_GenericAlias` of a type supported by the DTO factory type.

Closes #2500

litestar/dto/_backend.py

@@ -18,6 +18,7 @@
 )
 
 from msgspec import UNSET, Struct, UnsetType, convert, defstruct, field
+from typing_extensions import get_origin
 
 from litestar.dto._types import (
     CollectionType,
@@ -110,7 +111,7 @@ def __init__(
             rename_fields=self.dto_factory.config.rename_fields,
         )
         self.transfer_model_type = self.create_transfer_model_type(
-            model_name=model_type.__name__, field_definitions=self.parsed_field_definitions
+            model_name=(get_origin(model_type) or model_type).__name__, field_definitions=self.parsed_field_definitions
         )
         self.dto_data_type: type[DTOData] | None = None
 

litestar/dto/base_dto.py

@@ -5,7 +5,7 @@
 from inspect import getmodule
 from typing import TYPE_CHECKING, Collection, Generic, TypeVar
 
-from typing_extensions import NotRequired, TypedDict, get_type_hints
+from typing_extensions import NotRequired, TypedDict
 
 from litestar.dto._backend import DTOBackend
 from litestar.dto._codegen_backend import DTOCodegenBackend
@@ -17,6 +17,7 @@
 from litestar.types.builtin_types import NoneType
 from litestar.types.composite_types import TypeEncodersMap
 from litestar.typing import FieldDefinition
+from litestar.utils.typing import get_type_hints_with_generics_resolved
 
 if TYPE_CHECKING:
     from typing import Any, ClassVar, Generator
@@ -267,7 +268,9 @@ def get_model_type_hints(
 
         return {
             k: FieldDefinition.from_kwarg(annotation=v, name=k)
-            for k, v in get_type_hints(model_type, localns=namespace, include_extras=True).items()
+            for k, v in get_type_hints_with_generics_resolved(
+                model_type, localns=namespace, include_extras=True
+            ).items()
         }
 
     @staticmethod

litestar/dto/dataclass_dto.py

@@ -3,6 +3,8 @@
 from dataclasses import MISSING, fields, replace
 from typing import TYPE_CHECKING, Generic, TypeVar
 
+from typing_extensions import get_origin
+
 from litestar.dto.base_dto import AbstractDTO
 from litestar.dto.data_structures import DTOFieldDefinition
 from litestar.dto.field import DTO_FIELD_META_KEY, DTOField
@@ -29,7 +31,8 @@ class DataclassDTO(AbstractDTO[T], Generic[T]):
     def generate_field_definitions(
         cls, model_type: type[DataclassProtocol]
     ) -> Generator[DTOFieldDefinition, None, None]:
-        dc_fields = {f.name: f for f in fields(model_type)}
+        model_origin = get_origin(model_type) or model_type
+        dc_fields = {f.name: f for f in fields(model_origin)}
         for key, field_definition in cls.get_model_type_hints(model_type).items():
             if not (dc_field := dc_fields.get(key)):
                 continue
@@ -41,7 +44,7 @@ def generate_field_definitions(
                     field_definition=field_definition,
                     default_factory=default_factory,
                     dto_field=dc_field.metadata.get(DTO_FIELD_META_KEY, DTOField()),
-                    model_name=model_type.__name__,
+                    model_name=model_origin.__name__,
                 ),
                 name=key,
                 default=default,

litestar/typing.py

@@ -4,7 +4,21 @@
 from copy import deepcopy
 from dataclasses import dataclass, is_dataclass, replace
 from inspect import Parameter, Signature
-from typing import Any, AnyStr, Callable, Collection, ForwardRef, Literal, Mapping, Protocol, Sequence, TypeVar, cast
+from typing import (  # type: ignore[attr-defined]
+    Any,
+    AnyStr,
+    Callable,
+    ClassVar,
+    Collection,
+    ForwardRef,
+    Literal,
+    Mapping,
+    Protocol,
+    Sequence,
+    TypeVar,
+    _GenericAlias,  # pyright: ignore
+    cast,
+)
 
 from msgspec import UnsetType
 from typing_extensions import NotRequired, Required, Self, get_args, get_origin, get_type_hints, is_typeddict
@@ -442,6 +456,19 @@ def is_subclass_of(self, cl: type[Any] | tuple[type[Any], ...]) -> bool:
             if self.origin in UnionTypes:
                 return all(t.is_subclass_of(cl) for t in self.inner_types)
 
+            if isinstance(self.annotation, _GenericAlias) and self.origin not in (ClassVar, Literal):
+                cl_args = get_args(cl)
+                cl_origin = get_origin(cl) or cl
+                return (
+                    issubclass(self.origin, cl_origin)
+                    and (len(cl_args) == len(self.args) if cl_args else True)
+                    and (
+                        all(t.is_subclass_of(cl_arg) for t, cl_arg in zip(self.inner_types, cl_args))
+                        if cl_args
+                        else True
+                    )
+                )
+
             return self.origin not in UnionTypes and is_class_and_subclass(self.origin, cl)
 
         if self.annotation is AnyStr:

litestar/utils/typing.py

@@ -249,7 +249,9 @@ def get_type_hints_with_generics_resolved(
     if origin is None:
         # Implies the generic types have not been specified in the annotation
         type_hints = get_type_hints(annotation, globalns=globalns, localns=localns, include_extras=include_extras)
-        typevar_map = {p: p for p in annotation.__parameters__}
+        if not (parameters := getattr(annotation, "__parameters__", None)):
+            return type_hints
+        typevar_map = {p: p for p in parameters}
     else:
         type_hints = get_type_hints(origin, globalns=globalns, localns=localns, include_extras=include_extras)
         # the __parameters__ is only available on the origin itself and not the annotation

tests/unit/test_dto/test_factory/test_base_dto.py

@@ -2,14 +2,15 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import TYPE_CHECKING, Tuple, TypeVar, Union
+from typing import TYPE_CHECKING, Generic, Tuple, TypeVar, Union
 
 import pytest
 from typing_extensions import Annotated
 
 from litestar import Request
 from litestar.dto import DataclassDTO, DTOConfig
 from litestar.exceptions.dto_exceptions import InvalidAnnotationException
+from litestar.types.empty import Empty
 from litestar.typing import FieldDefinition
 
 from . import Model
@@ -19,7 +20,8 @@
 
     from litestar.dto._backend import DTOBackend
 
-T = TypeVar("T", bound=Model)
+T = TypeVar("T")
+ModelT = TypeVar("ModelT", bound=Model)
 
 
 def get_backend(dto_type: type[DataclassDTO[Any]]) -> DTOBackend:
@@ -77,7 +79,7 @@ def test_extra_annotated_metadata_ignored() -> None:
 
 def test_overwrite_config() -> None:
     first = DTOConfig(exclude={"a"})
-    generic_dto = DataclassDTO[Annotated[T, first]]  # pyright: ignore
+    generic_dto = DataclassDTO[Annotated[ModelT, first]]  # pyright: ignore
     second = DTOConfig(exclude={"b"})
     dto = generic_dto[Annotated[Model, second]]  # pyright: ignore
     assert dto.config is second
@@ -86,13 +88,13 @@ def test_overwrite_config() -> None:
 def test_existing_config_not_overwritten() -> None:
     assert getattr(DataclassDTO, "_config", None) is None
     first = DTOConfig(exclude={"a"})
-    generic_dto = DataclassDTO[Annotated[T, first]]  # pyright: ignore
+    generic_dto = DataclassDTO[Annotated[ModelT, first]]  # pyright: ignore
     dto = generic_dto[Model]  # pyright: ignore
     assert dto.config is first
 
 
 def test_config_assigned_via_subclassing() -> None:
-    class CustomGenericDTO(DataclassDTO[T]):
+    class CustomGenericDTO(DataclassDTO[ModelT]):
         config = DTOConfig(exclude={"a"})
 
     concrete_dto = CustomGenericDTO[Model]
@@ -161,3 +163,28 @@ class SubType(Model):
     assert (
         dto_type._dto_backends["handler_id"]["data_backend"].parsed_field_definitions[-1].name == "c"  # pyright: ignore
     )
+
+
+def test_type_narrowing_with_generic_type() -> None:
+    @dataclass
+    class Foo(Generic[T]):
+        foo: T
+
+    hints = DataclassDTO.get_model_type_hints(Foo[int])
+    assert hints == {
+        "foo": FieldDefinition(
+            raw=int,
+            annotation=int,
+            type_wrappers=(),
+            origin=None,
+            args=(),
+            metadata=(),
+            instantiable_origin=None,
+            safe_generic_origin=None,
+            inner_types=(),
+            default=Empty,
+            extra={},
+            kwarg_definition=None,
+            name="foo",
+        )
+    }

tests/unit/test_dto/test_integration.py

@@ -1,19 +1,22 @@
 from __future__ import annotations
 
-from typing import Dict
+from dataclasses import dataclass
+from typing import Dict, Generic, TypeVar
 from unittest.mock import MagicMock
 
 import pytest
 
 from litestar import Controller, Litestar, Router, post
 from litestar.config.app import ExperimentalFeatures
-from litestar.dto import AbstractDTO, DTOConfig
+from litestar.dto import AbstractDTO, DataclassDTO, DTOConfig, DTOData
 from litestar.dto._backend import DTOBackend
 from litestar.dto._codegen_backend import DTOCodegenBackend
 from litestar.testing import create_test_client
 
 from . import Model
 
+T = TypeVar("T")
+
 
 @pytest.fixture()
 def experimental_features(use_experimental_dto_backend: bool) -> list[ExperimentalFeatures] | None:
@@ -153,3 +156,23 @@ def handler(data: Model) -> Model:
 
     backend = handler.resolve_data_dto()._dto_backends[handler.handler_id]["data_backend"]  # type: ignore[union-attr]
     assert isinstance(backend, DTOBackend)
+
+
+def test_dto_for_generic_model() -> None:
+    @dataclass
+    class Foo(Generic[T]):
+        foo: T
+
+    FooDTO = DataclassDTO[Foo[int]]
+
+    @post("/foo", dto=FooDTO, signature_types=[Foo])
+    async def foo_handler(data: DTOData[Foo[int]]) -> Foo[int]:
+        return data.create_instance()
+
+    with create_test_client(route_handlers=foo_handler) as client:
+        response = client.post("/foo", json={"foo": 1})
+        assert response.status_code == 201
+        assert response.json() == {"foo": 1}
+        response = client.post("/foo", json={"foo": "1"})
+        assert response.status_code == 400
+        assert response.json() == {"status_code": 400, "detail": "Expected `int`, got `str` - at `$.foo`"}