This is because it is expected that **your users** would define the actual **URL path** where they want to receive the webhook request in some other way (e.g. a web dashboard).

### Check the docs

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

Let's imagine that loading the model can **take quite some time**, because it has to read a lot of **data from disk**. So you don't want to do it for every request.

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

Because of that, the JSON Schema for a model can be different depending on if it's used for **input or output**:

* for **input** the `description` will **not be required**

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

{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

Here we have an empty `yield` because we are actually not using the database object directly.

It is connecting to the database and storing the connection data in an internal variable that is independent for each request (using the `contextvars` tricks from above).

Because the database connection is potentially I/O blocking, this dependency is created with a normal `def` function.

## Use the instance as a dependency

Then, we could use this `checker` in a `Depends(checker)`, instead of `Depends(FixedContentQueryChecker)`, because the dependency is the instance, `checker`, not the class itself.

And when solving the dependency, **FastAPI** will call this `checker` like:

```Python
checker(q="somequery")
```

When you need to use the `common_parameters()` dependency, you have to write the whole parameter with the type annotation and `Depends()`:

```Python
commons: Annotated[dict, Depends(common_parameters)]
```

But because we are using `Annotated`, we can store that `Annotated` value in a variable and use it in multiple places:

=== "Python 3.10+"

    ```Python hl_lines="12  16  21"

!!! info
    To receive uploaded files, 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 uploaded files are sent as "form data".

## Import `File`

Import `File` and `UploadFile` from `fastapi`:

=== "Python 3.9+"

    ```Python hl_lines="3"

This gives you a lot of flexibility. You can return any data type, override any data declaration or validation, etc.

## Using the `jsonable_encoder` in a `Response`

Because **FastAPI** doesn't do any change to a `Response` you return, you have to make sure it's contents are ready for it.