/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

## Query Parameters with a Pydantic Model { #query-parameters-with-a-pydantic-model }

Declare the **query parameters** that you need in a **Pydantic model**, and then declare the parameter as `Query`:

{* ../../docs_src/query_param_models/tutorial001_an_py310.py hl[9:13,17] *}

/// note | Technical Details

You could also use `from starlette import status`.

**FastAPI** provides the same `starlette.status` as `fastapi.status` just as a convenience for you, the developer. But it comes directly from Starlette.

///

## Changing the default { #changing-the-default }

/// note

**FastAPI** saura que la valeur de `q` n'est pas requise grâce à la valeur par défaut `= None`.

Le `Union` dans `Union[str, None]` permettra à votre éditeur de vous offrir un meilleur support et de détecter les erreurs.

///

## Validation additionnelle

```JSON
{"item_id":3}
```

/// check

Notice that the value your function received (and returned) is `3`, as a Python `int`, not a string `"3"`.

So, with that type declaration, **FastAPI** gives you automatic request <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>.

///

## Data validation { #data-validation }

```JSON
{"item_id":3}
```

/// check | Revisa

Nota que el valor que tu función recibió (y devolvió) es `3`, como un `int` de Python, no un string `"3"`.

Entonces, con esa declaración de tipo, **FastAPI** te ofrece <abbr title="convertir el string que viene de un request HTTP en datos de Python">"parsing"</abbr> automático de request.

///

## Validación de datos { #data-validation }

# Öğren

**FastAPI** öğrenmek için giriş bölümleri ve öğreticiler burada yer alıyor.

}
```

### Setting the `root_path` in the FastAPI app { #setting-the-root-path-in-the-fastapi-app }

Alternatively, if you don't have a way to provide a command line option like `--root-path` or equivalent, you can set the `root_path` parameter when creating your FastAPI app:

{* ../../docs_src/behind_a_proxy/tutorial002_py39.py hl[3] *}

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

/// tip

This same technique applies to `Query`, `Cookie`, and `Header`. 😎

///

## Cookies with a Pydantic Model { #cookies-with-a-pydantic-model }

new_app = UnicornMiddleware(app, some_config="rainbow")
```

Mas, o FastAPI (na verdade, o Starlette) fornece uma maneira mais simples de fazer isso que garante que os middlewares internos lidem com erros do servidor e que os manipuladores de exceções personalizados funcionem corretamente.

Para isso, você usa `app.add_middleware()` (como no exemplo para CORS).

```Python
from fastapi import FastAPI
from unicorn import UnicornMiddleware

app = FastAPI()

# 直接返回响应

当你创建一个 **FastAPI** *路径操作* 时，你可以正常返回以下任意一种数据：`dict`，`list`，Pydantic 模型，数据库模型等等。

**FastAPI** 默认会使用 `jsonable_encoder` 将这些类型的返回值转换成 JSON 格式，`jsonable_encoder` 在 [JSON 兼容编码器](../tutorial/encoder.md){.internal-link target=_blank} 中有阐述。

然后，**FastAPI** 会在后台将这些兼容 JSON 的数据（比如字典）放到一个 `JSONResponse` 中，该 `JSONResponse` 会用来发送响应给客户端。

但是你可以在你的 *路径操作* 中直接返回一个 `JSONResponse`。

直接返回响应可能会有用处，比如返回自定义的响应头和 cookies。

## 返回 `Response`