Da wir im obigen Beispiel `user_dict` von `user_in.model_dump()` bekommen haben, wäre dieser Code:

```Python
user_dict = user_in.model_dump()
UserInDB(**user_dict)
```

gleichwertig zu:

```Python
UserInDB(**user_in.model_dump())
```

client = TestClient(app)


@pytest.mark.parametrize(
    ("user_id", "expected_response"),
    [
        ("me", {"user_id": "the current user"}),
        ("alice", {"user_id": "alice"}),
    ],
)
def test_get_users(user_id: str, expected_response: dict):
    response = client.get(f"/users/{user_id}")
    assert response.status_code == 200, response.text
    assert response.json() == expected_response

@user_router.get("/")
def get_users():
    return [{"user_id": "u1"}, {"user_id": "u2"}]


@user_router.get("/{user_id}")
def get_user(user_id: str):
    return {"user_id": user_id}


@item_router.get("/")
def get_items(user_id: Optional[str] = None):
    if user_id is None:
        return [{"item_id": "i1", "user_id": "u1"}, {"item_id": "i2", "user_id": "u2"}]
    else:

                                "schema": {"$ref": "#/components/schemas/UserIn"}
                            }
                        },
                        "required": True,
                    },
                }
            }
        },
        "components": {
            "schemas": {
                "UserIn": {
                    "title": "UserIn",
                    "required": ["username", "password", "email"],

                                "schema": {"$ref": "#/components/schemas/UserIn"}
                            }
                        },
                        "required": True,
                    },
                }
            }
        },
        "components": {
            "schemas": {
                "UserIn": {
                    "title": "UserIn",
                    "required": IsList(

                                },
                            }
                        },
                    },
                    "UserIn": {
                        "title": "UserIn",
                        "required": ["username", "email", "password"],
                        "type": "object",
                        "properties": {

                                "anyOf": [{"type": "string"}, {"type": "null"}],
                            },
                        },
                    },
                    "UserIn": {
                        "title": "UserIn",
                        "required": ["username", "password", "email"],
                        "type": "object",
                        "properties": {

    assert response.status_code == 200
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/users/{user_id}/items/{item_id}": {
                "get": {
                    "summary": "Read User Item",
                    "operationId": "read_user_item_users__user_id__items__item_id__get",
                    "parameters": [

`BaseUser` verfügt über die Basis-Felder. Dann erbt `UserIn` von `BaseUser` und fügt das Feld `password` hinzu, sodass es nun alle Felder beider Modelle hat.

Wir annotieren den Funktionsrückgabetyp als `BaseUser`, geben aber tatsächlich eine `UserIn`-Instanz zurück.

* Allow path parameters to have default values (e.g. `None`) and discard them instead of raising an error.
    * This allows declaring a parameter like `user_id: str = None` that can be taken from a query parameter, but the same *path operation* can be included in a router with a path `/users/{user_id}`, in which case will be taken from the path and will be required.