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

So, it won't expect to be accessed at `http://127.0.0.1:8000/api/v1/app`.

Uvicorn will expect the proxy to access Uvicorn at `http://127.0.0.1:8000/app`, and then it would be the proxy's responsibility to add the extra `/api/v1` prefix on top.

And you can declare some of the files as `bytes` and some as `UploadFile`.

!!! warning
    You can declare multiple `File` and `Form` parameters in a *path operation*, but you can't also declare `Body` fields that you expect to receive as JSON, as the request will have the body encoded using `multipart/form-data` instead of `application/json`.

    This is not a limitation of **FastAPI**, it's part of the HTTP protocol.

## Recap

    ```

=== "Python 3.8+"

    ```Python hl_lines="20"
    {!> ../../../docs_src/body_nested_models/tutorial004.py!}
    ```

This would mean that **FastAPI** would expect a body similar to:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {

* It exposes an actual Python <a href="https://docs.python.org/3/library/tempfile.html#tempfile.SpooledTemporaryFile" class="external-link" target="_blank">`SpooledTemporaryFile`</a> object that you can pass directly to other libraries that expect a file-like object.

### `UploadFile`

`UploadFile` has the following attributes:

* `filename`: A `str` with the original file name that was uploaded (e.g. `myimage.jpg`).

In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

!!! warning
    You can declare multiple `Form` parameters in a *path operation*, but you can't also declare `Body` fields that you expect to receive as JSON, as the request will have the body encoded using `application/x-www-form-urlencoded` instead of `application/json`.

    This is not a limitation of **FastAPI**, it's part of the HTTP protocol.

## Recap

!!! note
    If you use a response class with no media type, FastAPI will expect your response to have no content, so it will not document the response format in its generated OpenAPI docs.

## Use `ORJSONResponse`

    You can actually skip that extra header and it would still work.

    But it's provided here to be compliant with the specifications.

    Also, there might be tools that expect and use it (now or in the future) and that might be useful for you or your users, now or in the future.

    That's the benefit of standards...

## See it in action

They have proven to be **FastAPI Experts** by helping many others. ✨

!!! tip
    You could become an official FastAPI Expert too!

    Just [help others with questions in GitHub](help-fastapi.md#help-others-with-questions-in-github){.internal-link target=_blank}. 🤓

You can see the **FastAPI Experts** for:

!!! info
    A "bearer" token is not the only option.

    But it's the best one for our use case.

    And it might be the best for most use cases, unless you are an OAuth2 expert and know exactly why there's another option that suits better your needs.

    In that case, **FastAPI** also provides you with the tools to build it.