Before Starlette `0.24.0`, a new instance of each middleware class would be created when a new middleware was added. That normally was not a problem, unless the middleware class expected to be created only once, with only one instance, that happened in some cases. This upgrade would solve those cases (thanks [@adriangb](https://github.com/adriangb)! Starlette PR [#2017](https://github.com/encode/starlette/pull/2017)). Now the middleware class instances are created once, right before the first request...

    class SomeCustomClass(BaseModel):
        model_config = {"arbitrary_types_allowed": True}

        a_uuid: MyUuid

        @field_serializer("a_uuid")
        def serialize_a_uuid(self, v):
            return str(v)

    @app.get("/get_custom_class")
    def return_some_user():
        # Test that the fix also works for custom pydantic classes

WebSocketErrorModel: type[BaseModel] = create_model("WebSocket")


class FastAPIError(RuntimeError):
    """
    A generic, FastAPI-specific error.
    """


class DependencyScopeError(FastAPIError):
    """
    A dependency declared that it depends on another dependency with an invalid
    (narrower) scope.
    """


class ValidationException(Exception):
    def __init__(
        self,

Example:

    Source (English):

        «««
        <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel docs</a>
        »»»

    Result (German):

        «««
        <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel-Dokumentation</a>
        »»»

from pydantic import BaseModel, Field, ValidationError


class Person:
    def __init__(self, name: str):
        self.name = name


class Pet:
    def __init__(self, owner: Person, name: str):
        self.owner = owner
        self.name = name


@dataclass
class Item:
    name: str
    count: int


class DictablePerson(Person):
    def __iter__(self):

            else:
                # It would probably make more sense for all response classes to have an
                # explicit default status_code, and to extract it from them, instead of
                # doing this inspection tricks, that would probably be in the future
                # TODO: probably make status_code a default class attribute for all
                # responses in Starlette

def test_raises_pydantic_v1_model_in_endpoint_param() -> None:
    class ParamModelV1(BaseModel):
        name: str

    app = FastAPI()

    with pytest.raises(PydanticV1NotSupportedError):

        @app.post("/param")
        def endpoint(data: ParamModelV1):  # pragma: no cover
            return data


def test_raises_pydantic_v1_model_in_return_type() -> None:
    class ReturnModelV1(BaseModel):
        name: str

def test_propagates_pydantic2_model_config():
    app = FastAPI()

    class Missing:
        def __bool__(self):
            return False

    class EmbeddedModel(BaseModel):
        model_config = ConfigDict(arbitrary_types_allowed=True)
        value: Union[str, Missing] = Missing()

    class Model(BaseModel):
        model_config = ConfigDict(
            arbitrary_types_allowed=True,
        )

@pytest.fixture(name="client")
def get_client():
    from pydantic import BaseModel, ValidationInfo, field_validator

    app = FastAPI()

    class ModelB(BaseModel):
        username: str

    class ModelC(ModelB):
        password: str

    class ModelA(BaseModel):
        name: str
        description: Optional[str] = None
        foo: ModelB
        tags: dict[str, str] = {}

from typing_extensions import Literal, deprecated

from ._compat import (
    Undefined,
)

_Unset: Any = Undefined


class ParamTypes(Enum):
    query = "query"
    header = "header"
    path = "path"
    cookie = "cookie"


class Param(FieldInfo):  # type: ignore[misc]
    in_: ParamTypes

    def __init__(
        self,
        default: Any = Undefined,
        *,