"msg": "Field required",
                    "input": {"name": "Foo"},
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "price"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "msg": "Field required",
                    "input": {"name": "Foo"},
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "price"],
                    "msg": "field required",
                    "type": "value_error.missing",

from typing import List

from fastapi import FastAPI
from fastapi._compat import PYDANTIC_V2
from fastapi.testclient import TestClient
from pydantic import BaseModel, ConfigDict, Field

app = FastAPI()


class Model(BaseModel):
    name: str = Field(alias="alias")


class ModelNoAlias(BaseModel):
    name: str

    if PYDANTIC_V2:
        model_config = ConfigDict(
            json_schema_extra={

from .utils import needs_pydanticv2


@pytest.fixture(name="client")
def get_client():
    app = FastAPI()

    from pydantic import BaseModel, computed_field

    class Rectangle(BaseModel):
        width: int
        length: int

        @computed_field
        @property
        def area(self) -> int:
            return self.width * self.length

    @app.get("/")
    def read_root() -> Rectangle:

                """
                `username` string. The OAuth2 spec requires the exact field name
                `username`.
                """
            ),
        ],
        password: Annotated[
            str,
            Form(),
            Doc(
                """
                `password` string. The OAuth2 spec requires the exact field name
                `password".
                """
            ),
        ],

    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "missing",
                    "loc": ["query", "needy"],
                    "msg": "Field required",
                    "input": None,
                },
                {
                    "type": "int_parsing",
                    "loc": ["query", "skip"],

                    "type": "missing",
                    "loc": ["body", "file"],
                    "msg": "Field required",
                    "input": None,
                },
                {
                    "type": "missing",
                    "loc": ["body", "fileb"],
                    "msg": "Field required",
                    "input": None,
                },
                {

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

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

## `Field`のインポート

まず、以下のようにインポートします:

```Python hl_lines="4"
{!../../../docs_src/body_fields/tutorial001.py!}
```

!!! warning "注意"
    `Field`は他の全てのもの（`Query`、`Path`、`Body`など）とは違い、`fastapi`からではなく、`pydantic`から直接インポートされていることに注意してください。

## モデルの属性の宣言

以下のように`Field`をモデルの属性として使用することができます:

```Python hl_lines="11 12 13 14"