The new docs will include Pydantic v2 and will use <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a> (which is also based on SQLAlchemy) once it is updated to use Pydantic v2 as well.

You can use the same dependency overrides from [Testing Dependencies with Overrides](testing-dependencies.md){.internal-link target=_blank} to alter a database for testing.

* <a href="https://www.uvicorn.org/" class="external-link" target="_blank">Uvicorn</a>: a high performance ASGI server.
* <a href="https://pgjones.gitlab.io/hypercorn/" class="external-link" target="_blank">Hypercorn</a>: an ASGI server compatible with HTTP/2 and Trio among other features.
* <a href="https://github.com/django/daphne" class="external-link" target="_blank">Daphne</a>: the ASGI server built for Django Channels.

You will see the automatic API docs for the main app, including only its own _path operations_:

<img src="/img/tutorial/sub-applications/image01.png">

And then, open the docs for the sub-application, at <a href="http://127.0.0.1:8000/subapi/docs" class="external-link" target="_blank">http://127.0.0.1:8000/subapi/docs</a>.

!!! warning "Deprecated"
    This tutorial is deprecated and will be removed in a future version.

You can also use <a href="https://github.com/encode/databases" class="external-link" target="_blank">`encode/databases`</a> with **FastAPI** to connect to databases using `async` and `await`.

    ```Python
    {!> ../../../docs_src/security/tutorial001.py!}
    ```


## Run it

!!! info
    First install <a href="https://github.com/Kludex/python-multipart" class="external-link" target="_blank">`python-multipart`</a>.

    E.g. `pip install python-multipart`.

    This is because **OAuth2** uses "form data" for sending the `username` and `password`.

Run the example with:

<div class="termy">

FastAPI 🐕‍🦺 🔗 👈 <abbr title='sometimes also called "exit", "cleanup", "teardown", "close", "context managers", ...'>➕ 🔁 ⏮️ 🏁</abbr>.

👉, ⚙️ `yield` ↩️ `return`, &amp; ✍ ➕ 🔁 ⏮️.

!!! tip
    ⚒ 💭 ⚙️ `yield` 1️⃣ 👁 🕰.

!!! note "📡 ℹ"
    🙆 🔢 👈 ☑ ⚙️ ⏮️:

    * <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a> ⚖️

```

</div>

That command line program called `fastapi` is **FastAPI CLI**.

FastAPI CLI takes the path to your Python program and automatically detects the variable with the FastAPI (commonly named `app`) and how to import it, and then serves it.

For production you would use `fastapi run` instead. 🚀

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps

The process normally is that **you define** in your code what is the message that you will send, the **body of the request**.

    {!> ../../../docs_src/dependencies/tutorial011.py!}
    ```

In this case, this `__call__` is what **FastAPI** will use to check for additional parameters and sub-dependencies, and this is what will be called to pass a value to the parameter in your *path operation function* later.

## Parameterize the instance

And now, we can use `__init__` to declare the parameters of the instance that we can use to "parameterize" the dependency:

In an advanced scenario where you know you need the dependency to be called at every step (possibly multiple times) in the same request instead of using the "cached" value, you can set the parameter `use_cache=False` when using `Depends`:

=== "Python 3.8+"

    ```Python hl_lines="1"