# Body - Nested Models

With **FastAPI**, you can define, validate, document, and use arbitrarily deeply nested models (thanks to Pydantic).

## List fields

You can define an attribute to be a subtype. For example, a Python `list`:

=== "Python 3.10+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/body_nested_models/tutorial001_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="14"

                                if message.get_content_maintype() == "application":
                                    subtype = message.get_content_subtype()
                                    if subtype == "json" or subtype.endswith("+json"):
                                        json_body = await request.json()
                            if json_body != Undefined: