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 typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None, Query(min_length=3, max_length=50, regex="^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:

`Optional` 부분은 편집기에게 더 나은 지원을 제공하기 위해서만 사용됩니다.

///

또한 `Query`로 더 많은 매개변수를 전달할 수 있습니다. 지금의 경우 문자열에 적용되는 `max_length` 매개변수입니다:

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

이는 데이터를 검증할 것이고, 데이터가 유효하지 않다면 명백한 오류를 보여주며, OpenAPI 스키마 *경로 작동*에 매개변수를 문서화 합니다.

## 검증 추가

매개변수 `min_length` 또한 추가할 수 있습니다:

```Python hl_lines="9"
{!../../docs_src/query_params_str_validations/tutorial003.py!}
```

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


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

///

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

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

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

## 🚮 🌅 🔬

👆 💪 🚮 🔢 `min_length`:

//// tab | 🐍 3️⃣.6️⃣ & 🔛

```Python hl_lines="10"

from fastapi import FastAPI, Query

app = FastAPI()


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

from pydantic import BaseModel, Field

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = Field(
        default=None, title="The description of the item", max_length=300
    )
    price: float = Field(gt=0, description="The price must be greater than zero")
    tax: float | None = None


@app.put("/items/{item_id}")

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


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