`Optional` の部分は、エディターによるより良いサポートを可能にします。

そして、さらに多くのパラメータを`Query`に渡すことができます。この場合、文字列に適用される、`max_length`パラメータを指定します。

```Python
q: Union[str, None] = Query(default=None, max_length=50)
```

これにより、データを検証し、データが有効でない場合は明確なエラーを表示し、OpenAPIスキーマの　*path operation* にパラメータを記載します。

## バリデーションをさらに追加する

パラメータ`min_length`も追加することができます:

```Python hl_lines="10"
{!../../../docs_src/query_params_str_validations/tutorial003.py!}

⤴️, 👥 💪 🚶‍♀️ 🌅 🔢 `Query`. 👉 💼, `max_length` 🔢 👈 ✔ 🎻:

```Python
q: Union[str, None] = Query(default=None, max_length=50)
```

👉 🔜 ✔ 📊, 🎦 🆑 ❌ 🕐❔ 📊 🚫 ☑, & 📄 🔢 🗄 🔗 *➡ 🛠️*.

## 🚮 🌅 🔬

👆 💪 🚮 🔢 `min_length`:

=== "🐍 3️⃣.6️⃣ & 🔛"

    ```Python hl_lines="10"

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str = Query(default="fixedquery", min_length=3)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

async def b():
    pass  # pragma: no cover


client = TestClient(app)


def test_get_response():
    response = client.get("/a")
    assert response.status_code == 204, response.text
    assert "content-length" not in response.headers
    assert response.content == b""


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {

```Python
q: str = Query(default=None, max_length=50)
```

Isso irá validar os dados, mostrar um erro claro quando os dados forem inválidos, e documentar o parâmetro na *operação de rota* do esquema OpenAPI..

## Adicionando mais validações

Você também pode incluir um parâmetro `min_length`:

```Python hl_lines="10"

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[Union[str, None], Query(min_length=3, max_length=50)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None], Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

        Query(
            alias="item-query",
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
            max_length=50,
            pattern="^fixedquery$",
            deprecated=True,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:

...使得参数可选，等同于：

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

但是 `Query` 显式地将其声明为查询参数。

然后，我们可以将更多的参数传递给 `Query`。在本例中，适用于字符串的 `max_length` 参数：

```Python
q: Union[str, None] = Query(default=None, max_length=50)
```

将会校验数据，在数据无效时展示清晰的错误信息，并在 OpenAPI 模式的*路径操作*中记录该参​​数。

## 添加更多校验

你还可以添加 `min_length` 参数：

```Python hl_lines="10"
{!../../../docs_src/query_params_str_validations/tutorial003.py!}
```

## 添加正则表达式