# 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`:

//// tab | Python 3.10+

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

////

//// tab | Python 3.8+

```Python hl_lines="14"

                    {
                        "type": "value_error.extra",
                        "loc": ["header", "tool"],
                        "msg": "extra fields not permitted",
                    }
                )
            ]
        }
    )


def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")

                                    </la:info>
                                    <la:errors/>
                                </div>
                                    <%-- Form Fields --%>
                                <table class="table table-bordered">
                                    <tbody>
                                    <tr>

                                    </la:info>
                                    <la:errors/>
                                </div>
                                    <%-- Form Fields --%>
                                <table class="table table-bordered">
                                    <tbody>
                                    <tr>

                    # TODO: remove when deprecating Pydantic v1
                    {
                        "type": "value_error.extra",
                        "loc": ["query", "tool"],
                        "msg": "extra fields not permitted",
                    }
                )
            ]
        }
    )


def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")

OAuth2 specifies that when using the "password flow" (that we are using) the client/user must send a `username` and `password` fields as form data.

And the spec says that the fields have to be named like that. So `user-name` or `email` wouldn't work.

But don't worry, you can show it as you wish to your final users in the frontend.

     * we can reference a node whose fields have been cleared is inside the iterator (and presumably
     * only under concurrent modification).
     *
     * To access these fields when you know that they are not null, call the pred() and succ()
     * methods, which perform null checks before returning the fields.
     */
    @CheckForNull private AvlNode<E> pred;

	"strings"

	color "github.com/minio/minio/internal/color"
)

// Extra ASN1 OIDs that we may need to handle
var (
	oidEmailAddress = []int{1, 2, 840, 113549, 1, 9, 1}
)

// printName prints the fields of a distinguished name, which include such
// things as its common name and locality.
func printName(names []pkix.AttributeTypeAndValue, buf *strings.Builder) []string {
	values := []string{}
	for _, name := range names {

                                    </la:info>
                                    <la:errors/>
                                </div>
                                    <%-- Form Fields --%>
                                <table class="table table-bordered">
                                    <tbody>
                                    <tr>

                                    </la:info>
                                    <la:errors/>
                                </div>
                                    <%-- Form Fields --%>
                                <table class="table table-bordered">
                                    <tbody>
                                    <tr>