```

!!! tip
    The `callback_url` query parameter uses a Pydantic <a href="https://docs.pydantic.dev/latest/concepts/types/#urls" class="external-link" target="_blank">URL</a> type.

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback

The actual callback code will depend heavily on your own API app.

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Just Modern Python

It's all based on standard **Python type** declarations (thanks to Pydantic). No new syntax to learn. Just standard modern Python.

If you need a 2 minute refresher of how to use Python types (even if you don't use FastAPI), check the short tutorial: [Python Types](python-types.md){.internal-link target=_blank}.

{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

For the **next request**, as we will reset that context variable again in the `async` dependency `reset_db_state()` and then create a new connection in the `get_db()` dependency, that new request will have its own database state (connection, transactions, etc).

!!! tip

如果您选择 "Watching" 而不是 "Releases only"，有人创建新 Issue 时，您会接收到通知。

然后您就可以尝试并帮助他们解决问题。

## 创建 Issue

您可以在 GitHub 资源库中<a href="https://github.com/tiangolo/fastapi/issues/new/choose" class="external-link" target="_blank">创建 Issue</a>，例如：

* 提出**问题**或**意见**
* 提出新**特性**建议

**注意**：如果您创建 Issue，我会要求您也要帮助别的用户。😉

## 创建 PR

<blockquote markdown="1">

**FastAPI** wouldn't exist if not for the previous work of others.

There have been many tools created before that have helped inspire its creation.

I have been avoiding the creation of a new framework for several years. First I tried to solve all the features covered by **FastAPI** using many different frameworks, plug-ins, and tools.

    Using these `dependencies` in the *path operation decorator* you can make sure they are executed while avoiding editor/tooling errors.

    It might also help avoid confusion for new developers that see an unused parameter in your code and could think it's unnecessary.

!!! info
    In this example we use invented custom headers `X-Key` and `X-Token`.

    * `200` is the default status code, which means everything was "OK".
    * Another example would be `201`, "Created". It is commonly used after creating a new record in the database.
    * A special case is `204`, "No Content".  This response is used when there is no content to return to the client, and so the response must not have a body.

    ```

### Declare the dependency, in the "dependant"

The same way you use `Body`, `Query`, etc. with your *path operation function* parameters, use `Depends` with a new parameter:

=== "Python 3.10+"

    ```Python hl_lines="13  18"
    {!> ../../../docs_src/dependencies/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="15  20"

    # can create race conditions/deadlocks if the context manager itself
    # has its own internal pool (e.g. a database connection pool)
    # to avoid this we let __exit__ run without a capacity limit
    # since we're creating a new limiter for each call, any non-zero limit
    # works (1 is arbitrary)
    exit_limiter = CapacityLimiter(1)
    try:
        yield await run_in_threadpool(cm.__enter__)
    except Exception as e:
        ok = bool(

Vous pouvez alors essayer de les aider à résoudre ces problèmes.

## Créer une Issue

Vous pouvez <a href="https://github.com/tiangolo/fastapi/issues/new/choose" class="external-link" target="_blank">créer une Issue</a> dans le dépôt GitHub, par exemple pour :

* Poser une question ou s'informer sur un problème.
* Suggérer une nouvelle fonctionnalité.