</div>

Bu, alanın **her zaman bir değeri olacağı** anlamına gelir; sadece bazen bu değer `None` olabilir (JSON'da `null`).

Dolayısıyla API'nizi kullanan client'ların bu değerin var olup olmadığını kontrol etmesine gerek yoktur; **alanın her zaman mevcut olacağını varsayabilirler**, sadece bazı durumlarda default değer olan `None` gelecektir.

try:
    from fastapi_cli.cli import main as cli_main

except ImportError:  # pragma: no cover
    cli_main = None  # type: ignore


def main() -> None:
    if not cli_main:  # type: ignore[truthy-function]  # ty: ignore[unused-ignore-comment]
        message = 'To use the fastapi command, please install "fastapi[standard]":\n\n\tpip install "fastapi[standard]"\n'
        print(message)
        raise RuntimeError(message)  # noqa: B904

client = TestClient(
    app,
    base_url="https://example.com",
    follow_redirects=False,
)


def test_redirect() -> None:
    response = client.get("/items")
    assert response.status_code == 307
    assert response.headers["location"] == "https://example.com/items/"


def test_no_redirect() -> None:
    response = client.get("/items/")
    assert response.status_code == 200

    sponsors_token: SecretStr
    pr_token: SecretStr
    github_repository: str
    httpx_timeout: int = 30


def get_graphql_response(
    *,
    settings: Settings,
    query: str,
    after: str | None = None,
) -> dict[str, Any]:
    headers = {"Authorization": f"token {settings.sponsors_token.get_secret_value()}"}
    variables = {"after": after}
    response = httpx.post(
        github_graphql_url,

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float = 10.5
    tags: list[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},
    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}

@app.put("/items/{item_id}")
async def read_items(
    item_id: UUID,
    start_datetime: datetime = Body(),
    end_datetime: datetime = Body(),
    process_after: timedelta = Body(),
    repeat_at: time | None = Body(default=None),
):
    start_process = start_datetime + process_after
    duration = end_datetime - start_process
    return {
        "item_id": item_id,
        "start_datetime": start_datetime,

```
http://127.0.0.1:8000/items/?skip=20
```

查询参数的值就是：

* `skip=20`：在 URL 中设定的值
* `limit=10`：使用默认值

## 可选参数 { #optional-parameters }

同理，把默认值设为 `None` 即可声明可选的查询参数：

{* ../../docs_src/query_params/tutorial002_py310.py hl[7] *}

本例中，查询参数 `q` 是可选的，默认值为 `None`。

/// check | 检查

注意，**FastAPI** 可以识别出 `item_id` 是路径参数，`q` 不是路径参数，而是查询参数。

///

## 查询参数类型转换 { #query-parameter-type-conversion }

</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):

    )
    assert response.status_code == 200
    assert response.json() == {
        "item_id": 123,
        "name": "Foo",
        "price": 50.1,
        "description": None,
        "tax": None,
    }


def test_put_with_no_data(client: TestClient):
    response = client.put("/items/123", json={})
    assert response.status_code == 422
    assert response.json() == {
        "detail": [