Here's a tip from my very **subjective** point of view:

* 🚨 Avoid using `Optional[SomeType]`
* Instead ✨ **use `Union[SomeType, None]`** ✨.

Both are equivalent and underneath they are the same, but I would recommend `Union` instead of `Optional` because the word "**optional**" would seem to imply that the value is optional, and it actually means "it can be `None`", even if it's not optional and is still required.

And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

/// info

Keep in mind that dataclasses can't do everything Pydantic models can do.

So, you might still need to use Pydantic models.

But there are situations where you might need to access the `Request` object directly.

## Details about the `Request` object { #details-about-the-request-object }

As **FastAPI** is actually **Starlette** underneath, with a layer of several tools on top, you can use Starlette's [`Request`](https://www.starlette.dev/requests/) object directly when you need to.

## HTTPX { #httpx }

Even if your **FastAPI** application uses normal `def` functions instead of `async def`, it is still an `async` application underneath.

`UploadFile` has the following `async` methods. They all call the corresponding file methods underneath (using the internal `SpooledTemporaryFile`).

* `write(data)`: Writes `data` (`str` or `bytes`) to the file.
* `read(size)`: Reads `size` (`int`) bytes/characters of the file.

Because of that, it's now recommended to instead use the `lifespan` as explained above.

## Technical Details { #technical-details }

Just a technical detail for the curious nerds. 🤓

Underneath, in the ASGI technical specification, this is part of the [Lifespan Protocol](https://asgi.readthedocs.io/en/latest/specs/lifespan.html), and it defines events called `startup` and `shutdown`.

/// info

Import `SQLModel` and create a database model:

{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[1:11] hl[7:11] *}

The `Hero` class is very similar to a Pydantic model (in fact, underneath, it actually *is a Pydantic model*).

There are a few differences:

$ python main.py

I solemnly swear 🐺
```

</div>

## Alternatives { #alternatives }

This is a simple guide to get you started and teach you how everything works **underneath**.

There are many **alternatives** to managing virtual environments, package dependencies (requirements), projects.

In the chapters about security, there are utility functions that are implemented in this same way.

If you understood all this, you already know how those utility tools for security work underneath.

///

## Dependencies with `yield`, `HTTPException`, `except` and Background Tasks { #dependencies-with-yield-httpexception-except-and-background-tasks }

/// warning

### [Django REST Framework](https://www.django-rest-framework.org/) { #django-rest-framework }

Django REST framework was created to be a flexible toolkit for building Web APIs using Django underneath, to improve its API capabilities.

It is used by many companies including Mozilla, Red Hat and Eventbrite.