# 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"

    ```

=== "Python 3.8+"

    ```Python hl_lines="15-23"
    {!> ../../../docs_src/schema_extra_example/tutorial001.py!}
    ```

这些额外的信息将按原样添加到输出的JSON模式中。

## `Field` 的附加参数

在 `Field`, `Path`, `Query`, `Body` 和其他你之后将会看到的工厂函数，你可以为JSON 模式声明额外信息，你也可以通过给工厂函数传递其他的任意参数来给JSON 模式声明额外信息，比如增加 `example`:

=== "Python 3.10+"

    ```Python hl_lines="2  8-11"

### 🖼 🩺 🎚

⏮️ `examples` 🚮 `Body()` `/docs` 🔜 👀 💖:

<img src="/img/tutorial/body-fields/image02.png">

## 📡 ℹ

!!! warning
    👉 📶 📡 ℹ 🔃 🐩 **🎻 🔗** &amp; **🗄**.

    🚥 💭 🔛 ⏪ 👷 👆, 👈 💪 🥃, &amp; 👆 🎲 🚫 💪 👉 ℹ, 💭 🆓 🚶 👫.

🕐❔ 👆 🚮 🖼 🔘 Pydantic 🏷, ⚙️ `schema_extra` ⚖️ `Field(example="something")` 👈 🖼 🚮 **🎻 🔗** 👈 Pydantic 🏷.

                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "password"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "loc": ["query", "token"],
                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["query", "token"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "loc": ["query", "token"],
                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["query", "token"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "loc": ["query", "query"],
                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["query", "query"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "type": "missing",
                    "loc": ["header", "x-token"],
                    "msg": "Field required",
                    "input": None,
                },
                {
                    "type": "missing",
                    "loc": ["header", "x-key"],
                    "msg": "Field required",
                    "input": None,
                },
            ]
        }
    ) | IsDict(

        return False
    else:
        assert isinstance(
            param_field.field_info, params.Body
        ), f"Param: {param_field.name} can only be a request body, using Body()"
        return True


def add_param_to_fields(*, field: ModelField, dependant: Dependant) -> None:
    field_info = field.field_info
    field_info_in = getattr(field_info, "in_", None)

class CallableGenDependency:
    def __call__(self, value: str) -> Generator[str, None, None]:
        yield value


class AsyncCallableDependency:
    async def __call__(self, value: str) -> str:
        return value


class AsyncCallableGenDependency:
    async def __call__(self, value: str) -> AsyncGenerator[str, None]:
        yield value


class MethodsDependency:
    def synchronous(self, value: str) -> str: