she had never done such a thing before, but she remembered having
seen in her brother's Latin Grammar, `A mouse--of a mouse--to a
mouse--a mouse--O mouse!'  The Mouse looked at her rather
inquisitively, and seemed to her to wink with one of its little
eyes, but it said nothing.

  `Perhaps it doesn't understand English,' thought Alice; `I
daresay it's a French mouse, come over with William the

# Body - Multiple Parameters

Now that we have seen how to use `Path` and `Query`, let's see more advanced uses of request body declarations.

## Mix `Path`, `Query` and body parameters

First, of course, you can mix `Path`, `Query` and request body parameter declarations freely and **FastAPI** will know what to do.

And you can also declare body parameters as optional, by setting the default to `None`:

=== "Python 3.10+"

## Running on Startup

In most cases, when you create a web API, you want it to be **always running**, uninterrupted, so that your clients can always access it. This is of course, unless you have a specific reason why you want it to run only in certain situations, but most of the time you want it constantly running and **available**.

### In a Remote Server

So, even with the code above that doesn't use Pydantic explicitly, FastAPI is using Pydantic to convert those standard dataclasses to Pydantic's own flavor of dataclasses.

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.

<img src="/img/tutorial/security/image02.png">

!!! note
    It doesn't matter what you type in the form, it won't work yet. But we'll get there.

This is of course not the frontend for the final users, but it's a great automatic tool to document interactively all your API.

It can be used by the frontend team (that can also be yourself).

# Learn

Here are the introductory sections and the tutorials to learn **FastAPI**.

## External Courses

Although the [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} and this **Advanced User Guide** are written as a guided tutorial (like a book) and should be enough for you to **learn FastAPI**, you might want to complement it with additional courses.

Or it might be the case that you just prefer to take other courses because they adapt better to your learning style.

We get the same response:

```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

but this time at the URL with the prefix path provided by the proxy: `/api/v1`.

Of course, the idea here is that everyone would access the app through the proxy, so the version with the path prefix `/api/v1` is the "correct" one.

she had never done such a thing before, but she remembered having
seen in her brother's Latin Grammar, `A mouse--of a mouse--to a
mouse--a mouse--O mouse!'  The Mouse looked at her rather
inquisitively, and seemed to her to wink with one of its little
eyes, but it said nothing.

  `Perhaps it doesn't understand English,' thought Alice; `I
daresay it's a French mouse, come over with William the

| `Forwarded`   | For outgoing requests, the original source IP. Note that since we spoof IPs in most cases, this usually is the same as the actual IP seen. For incoming requests, this is used only for traffic from waypoints (which are trusted and cannot spoof IPs) |