name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


class User(BaseModel):
    username: str
    full_name: Union[str, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Item,
    user: User,
    importance: Annotated[int, Body(gt=0)],
    q: Union[str, None] = None,
):

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


@app.put("/items/{item_id}")
async def update_item(
    item_id: Annotated[int, Path(title="The ID of the item to get", ge=0, le=1000)],
    q: str | None = None,
    item: Item | None = None,
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

//// tab | Python 3.10+

```Python
q: str | None = None
```

////

//// tab | Python 3.9+

```Python
q: Union[str, None] = None
```

////

Мы «обернём» это в `Annotated`, и получится:

//// tab | Python 3.10+

```Python
q: Annotated[str | None] = None
```

////

//// tab | Python 3.9+

```Python
q: Annotated[Union[str, None]] = None
```

////

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    item_id: Annotated[int, Path(title="The ID of the item to get", ge=0, le=1000)],
    q: Union[str, None] = None,
    item: Union[Item, None] = None,
):
    results = {"item_id": item_id}
    if q:

from typing import Annotated

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Annotated[Item, Body(embed=True)]):
    results = {"item_id": item_id, "item": item}

代替：

```Python
q: Union[str, None] = None
```

但是现在我们正在用 `Query` 声明它，例如：

```Python
q: Union[str, None] = Query(default=None, min_length=3)
```

因此，当你在使用 `Query` 且需要声明一个值是必需的时，只需不声明默认参数：

{* ../../docs_src/query_params_str_validations/tutorial006.py hl[7] *}

### 使用`None`声明必需参数

你可以声明一个参数可以接收`None`值，但它仍然是必需的。这将强制客户端发送一个值，即使该值是`None`。

为此，你可以声明`None`是一个有效的类型，并仍然使用`default=...`：

@app.post("/optional-list-str", operation_id="optional_list_str")
async def read_optional_list_str(
    p: Annotated[Optional[list[str]], Body(embed=True)] = None,
):
    return {"p": p}


class BodyModelOptionalListStr(BaseModel):
    p: Optional[list[str]] = None


@app.post("/model-optional-list-str", operation_id="model_optional_list_str")
async def read_model_optional_list_str(p: BodyModelOptionalListStr):

app = FastAPI()


class UserIn(BaseModel):
    username: str
    password: str
    email: EmailStr
    full_name: Union[str, None] = None


class UserOut(BaseModel):
    username: str
    email: EmailStr
    full_name: Union[str, None] = None


@app.post("/user/", response_model=UserOut)
async def create_user(user: UserIn) -> Any:

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


@app.put("/items/{item_id}")
async def update_item(
    item_id: int,
    item: Item = Body(
        examples=[
            {
                "name": "Foo",
                "description": "A very nice Item",

from typing import Annotated, Union

from fastapi import Cookie, Depends, FastAPI

app = FastAPI()


def query_extractor(q: Union[str, None] = None):
    return q


def query_or_cookie_extractor(
    q: Annotated[str, Depends(query_extractor)],
    last_query: Annotated[Union[str, None], Cookie()] = None,
):
    if not q:
        return last_query
    return q


@app.get("/items/")
async def read_query(