# Advanced Dependencies

## Parameterized dependencies

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

So, you could add additional data to the automatically generated schema.

For example, you could decide to read and validate the request with your own code, without using the automatic features of FastAPI with Pydantic, but you could still want to define the request in the OpenAPI schema.

You could do that with `openapi_extra`:

```Python hl_lines="20-37  39-40"

            Any,
            Doc(
                """
                The type to use for the response.

                It could be any valid Pydantic *field* type. So, it doesn't have to
                be a Pydantic model, it could be other things, like a `list`, `dict`,
                etc.

                It will be used for:

👆 💪 ✍ & ⚙️ 🌐 🔢 🐚, 🍵 💆‍♂ 🐍:

=== "💾, 🇸🇻, 🚪 🎉"

    <div class="termy">

    ```console
    // You could create an env var MY_NAME with
    $ export MY_NAME="Wade Wilson"

    // Then you could use it with other programs, like
    $ echo "Hello $MY_NAME"

    Hello Wade Wilson
    ```

    </div>

=== "🚪 📋"

    <div class="termy">

    {!> ../../../docs_src/body_multiple_params/tutorial001.py!}
    ```

!!! note
    Notice that, in this case, the `item` that would be taken from the body is optional. As it has a `None` default value.

## Multiple body parameters

In the previous example, the *path operations* would expect a JSON body with the attributes of an `Item`, like:

```JSON
{
    "name": "Foo",
    "description": "The pretender",

If it was in a type annotation we could have used the vertical bar, as:

```Python
some_variable: PlaneItem | CarItem
```

But if we put that in `response_model=PlaneItem | CarItem` we would get an error, because Python would try to perform an **invalid operation** between `PlaneItem` and `CarItem` instead of interpreting that as a type annotation.

This client could be a browser with a frontend, a code from someone else, an IoT device, etc.

You could need to tell the client that:

* The client doesn't have enough privileges for that operation.
* The client doesn't have access to that resource.
* The item the client was trying to access doesn't exist.
* etc.

```
.
├── app
│   ├── __init__.py
│   ├── main.py
│   └── test_main.py
```

The file `main.py` would have:

```Python
{!../../../docs_src/async_tests/main.py!}
```

The file `test_main.py` would have the tests for `main.py`, it could look like this now:

```Python
{!../../../docs_src/async_tests/test_main.py!}
```

## Run it

You can run your tests as usual via:

<img src="/img/tutorial/extending-openapi/image03.png">

## Change the Theme

The same way you could set the syntax highlighting theme with the key `"syntaxHighlight.theme"` (notice that it has a dot in the middle):

```Python hl_lines="3"
{!../../../docs_src/configure_swagger_ui/tutorial002.py!}
```

That configuration would change the syntax highlighting color theme:

<img src="/img/tutorial/extending-openapi/image04.png">

</blockquote>

## Investigation

By using all the previous alternatives I had the chance to learn from all of them, take ideas, and combine them in the best way I could find for myself and the teams of developers I have worked with.

For example, it was clear that ideally it should be based on standard Python type hints.

Also, the best approach was to use already existing standards.