Isso é útil para operações que precisam acontecer após uma solicitação, mas que o cliente realmente não precisa esperar a operação ser concluída para receber a resposta.

Isso inclui, por exemplo:

- Envio de notificações por email após a realização de uma ação:

## Lista de parâmetros de consulta / múltiplos valores

Quando você declara explicitamente um parâmetro com `Query` você pode declará-lo para receber uma lista de valores, ou podemos dizer, que irá receber mais de um valor.

Por exemplo, para declarar que o parâmetro `q` pode aparecer diversas vezes na URL, você escreveria:

```Python hl_lines="9"

<img src="/img/tutorial/websockets/image05.png">

## Verbindungsabbrüche und mehreren Clients handhaben

Wenn eine WebSocket-Verbindung geschlossen wird, löst `await websocket.receive_text()` eine `WebSocketDisconnect`-Exception aus, die Sie dann wie in folgendem Beispiel abfangen und behandeln können.

=== "Python 3.9+"

    ```Python hl_lines="79-81"

    # TODO: remove after upgrading python-jose to a version that explicitly supports Python 3.12
    # also, if it won't receive an update, consider replacing python-jose with some alternative
    # related issues:
    #   - https://github.com/mpdavis/python-jose/issues/332
    #   - https://github.com/mpdavis/python-jose/issues/334

...But here I want to show you the community.

---

**FastAPI** receives a lot of support from the community. And I want to highlight their contributions.

These are the people that:

Those worker processes would be the ones running your application, they would perform the main computations to receive a **request** and return a **response**, and they would load anything you put in variables in RAM.

<img src="/img/deployment/concepts/process-ram.svg">

Para o `await` funcionar, tem que estar dentro de uma função que suporte essa assincronicidade. Para fazer isso, apenas declare a função com `async def`:

```Python hl_lines="1"

If you depended on exceptions not being received by dependencies with `yield`, and receiving an exception breaks the code after `yield`, you can use a block with `try` and `finally`:

```Python
async def do_something():
    try:
        yield something

Let's imagine that you have a database `fake_db` that only receives JSON compatible data.

For example, it doesn't receive `datetime` objects, as those are not compatible with JSON.

So, a `datetime` object would have to be converted to a `str` containing the data in <a href="https://en.wikipedia.org/wiki/ISO_8601" class="external-link" target="_blank">ISO format</a>.

}
```

and it would expect a response from that *external API* with a JSON body like:

```JSON
{
    "ok": true
}
```

!!! tip
    Notice how the callback URL used contains the URL received as a query parameter in `callback_url` (`https://www.external.org/events`) and also the invoice `id` from inside of the JSON body (`2expen51ve`).

### Add the callback router