```python
from fastapi import FastAPI
```

::: fastapi.FastAPI
    options:
        members:
            - openapi_version
            - webhooks
            - state
            - dependency_overrides
            - openapi
            - websocket
            - include_router
            - get
            - put
            - post
            - delete
            - options

    我们将`SessionLocal()`请求的创建和处理放在一个`try`块中。

    然后我们在finally块中关闭它。

    通过这种方式，我们确保数据库会话在请求后始终关闭，即使在处理请求时出现异常也会关闭。

### 关于`request.state`

`request.state`是每个`Request`对象的属性。它用于存储附加到请求本身的任意对象，例如本例中的数据库会话。您可以在[Starlette 的关于`Request`state](https://www.starlette.io/requests/#other-state)的文档中了解更多信息。

对于这种情况下，它帮助我们确保在所有请求中使用单个数据库会话，然后关闭（在中间件中）。

### 使用`yield`依赖项与使用中间件的区别

在此处添加**中间件**与`yield`的依赖项的作用效果类似，但也有一些区别：

            - url
            - base_url
            - headers
            - query_params
            - path_params
            - cookies
            - client
            - state
            - url_for
            - client_state
            - application_state
            - receive
            - send
            - accept
            - receive_text
            - receive_bytes
            - receive_json
            - iter_text

    # Including PR: https://github.com/encode/httpx/pull/2309
    "ignore:'cgi' is deprecated:DeprecationWarning",
    # For passlib
    "ignore:'crypt' is deprecated and slated for removal in Python 3.13:DeprecationWarning",
    # see https://trio.readthedocs.io/en/stable/history.html#trio-0-22-0-2022-09-28
    "ignore:You seem to already have a custom.*:RuntimeWarning:trio",

     & ⤴️ 👥 🔐 ⚫️ `finally` 🍫.

    👉 🌌 👥 ⚒ 💭 💽 🎉 🕧 📪 ⏮️ 📨. 🚥 📤 ⚠ ⏪ 🏭 📨.

### 🔃 `request.state`

`request.state` 🏠 🔠 `Request` 🎚. ⚫️ 📤 🏪 ❌ 🎚 📎 📨 ⚫️, 💖 💽 🎉 👉 💼. 👆 💪 ✍ 🌅 🔃 ⚫️ <a href="https://www.starlette.io/requests/#other-state" class="external-link" target="_blank">💃 🩺 🔃 `Request` 🇵🇸</a>.

👥 👉 💼, ⚫️ ℹ 👥 🚚 👁 💽 🎉 ⚙️ 🔘 🌐 📨, &amp; ⤴️ 🔐 ⏮️ (🛠️).

legacy_request_state_context_var: ContextVar[Optional[Dict[str, Any]]] = ContextVar(
    "legacy_request_state_context_var", default=None
)

async def set_up_request_state_dependency():
    request_state = {"user": "deadpond"}
    contextvar_token = legacy_request_state_context_var.set(request_state)
    yield request_state
    legacy_request_state_context_var.reset(contextvar_token)
```

```python
from fastapi import FastAPI
```

::: fastapi.FastAPI
    options:
        members:
            - openapi_version
            - webhooks
            - state
            - dependency_overrides
            - openapi
            - websocket
            - include_router
            - get
            - put
            - post
            - delete
            - options

<img src="/img/tutorial/response-status-code/image01.png">

!!! note
    Some response codes (see the next section) indicate that the response does not have a body.

    FastAPI knows this, and will produce OpenAPI docs that state there is no response body.

## About HTTP status codes

!!! note
    If you already know what HTTP status codes are, skip to the next section.

```Python
# db._state = PeeweeConnectionState()
```

And in the file `sql_app/main.py` file, comment the body of the `async` dependency `reset_db_state()` and replace it with a `pass`:

```Python
async def reset_db_state():
#     database.db._state._state.set(db_state_default.copy())
#     database.db._state.reset()
    pass
```

Then run your app with Uvicorn:

## Recap

Use multiple Pydantic models and inherit freely for each case.