In some cases, you might still have to use Pydantic's version of `dataclasses`. For example, if you have errors with the automatically generated API documentation.

In that case, you can simply swap the standard `dataclasses` with `pydantic.dataclasses`, which is a drop-in replacement:

```{ .python .annotate hl_lines="1  5  8-11  14-17  23-25  28" }
{!../../../docs_src/dataclasses/tutorial003.py!}
```

```Python hl_lines="11  14-16"
{!../../../docs_src/sub_applications/tutorial001.py!}
```

### Mount the sub-application

In your top-level application, `app`, mount the sub-application, `subapi`.

In this case, it will be mounted at the path `/subapi`:

```Python hl_lines="11  19"
{!../../../docs_src/sub_applications/tutorial001.py!}
```

### Check the automatic API docs

{!../../../docs_src/async_sql_databases/tutorial001.py!}
```

!!! tip
    If you were connecting to a different database (e.g. PostgreSQL), you would need to change the `DATABASE_URL`.

## Create the tables

In this case, we are creating the tables in the same Python file, but in production, you would probably want to create them with Alembic, integrated with migrations, etc.

    {!> ../../../docs_src/extra_models/tutorial005.py!}
    ```

## Recap

Use multiple Pydantic models and inherit freely for each case.

        original_type = cast(Type[BaseModel], original_type)
        use_type = cloned_types.get(original_type)
        if use_type is None:
            use_type = create_model(original_type.__name__, __base__=original_type)
            cloned_types[original_type] = use_type
            for f in original_type.__fields__.values():
                use_type.__fields__[f.name] = create_cloned_field(

## Use Case

Let's start with an example **use case** and then see how to solve it with this.

Let's imagine that you have some **machine learning models** that you want to use to handle requests. 🤖

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

        ```

    * So, the colon in `main:app` would be equivalent to the Python `import` part in `from main import app`.

* `--workers`: The number of worker processes to use, each will run a Uvicorn worker, in this case, 4 workers.

* `--worker-class`: The Gunicorn-compatible worker class to use in the worker processes.
    * Here we pass the class that Gunicorn can import and use with:

        ```Python

::: fastapi.WebSocket
    options:
        members:
            - scope
            - app
            - url
            - base_url
            - headers
            - query_params
            - path_params
            - cookies
            - client
            - state
            - url_for
            - client_state

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  - contributing.md
- release-notes.md
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