为此，你可以声明`None`是一个有效的类型，并仍然使用`default=...`：

{* ../../docs_src/query_params_str_validations/tutorial006c.py hl[9] *}

/// tip

Pydantic 是 FastAPI 中所有数据验证和序列化的核心，当你在没有设默认值的情况下使用 `Optional` 或 `Union[Something, None]` 时，它具有特殊行为，你可以在 Pydantic 文档中阅读有关<a href="https://docs.pydantic.dev/latest/concepts/models/#required-optional-fields" class="external-link" target="_blank">必需可选字段</a>的更多信息。

///

## 查询参数列表 / 多个值

from fastapi.logger import logger
from pydantic import (
    AnyUrl,
    BaseModel,
    Field,
    GetJsonSchemaHandler,
)
from typing_extensions import Literal, TypedDict
from typing_extensions import deprecated as typing_deprecated

try:
    import email_validator

    assert email_validator  # make autoflake ignore the unused import
    from pydantic import EmailStr
except ImportError:  # pragma: no cover

    - deployment/cloud.md
    - deployment/server-workers.md
    - deployment/docker.md
  - How To - Recipes:
    - how-to/index.md
    - how-to/general.md
    - how-to/migrate-from-pydantic-v1-to-pydantic-v2.md
    - how-to/graphql.md
    - how-to/custom-request-and-route.md
    - how-to/conditional-openapi.md
    - how-to/extending-openapi.md
    - how-to/separate-openapi-schemas.md

/// info | Info

Beachten Sie, dass der `TestClient` Daten empfängt, die nach JSON konvertiert werden können, keine Pydantic-Modelle.

    "price": 42.0,
    "tax": 3.2
}
```

但是你也可以声明多个请求体参数，例如 `item` 和 `user`：

{* ../../docs_src/body_multiple_params/tutorial002_py310.py hl[20] *}

在这种情况下，**FastAPI** 将注意到该函数中有多个请求体参数（两个 Pydantic 模型参数）。

因此，它将使用参数名称作为请求体中的键（字段名称），并期望一个类似于以下内容的请求体：

```JSON
{
    "item": {
        "name": "Foo",
        "description": "The pretender",
        "price": 42.0,
        "tax": 3.2
    },

from fastapi import FastAPI
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class Items(BaseModel):
    items: dict[str, int]


@app.post("/foo")
def foo(items: Items):
    return items.items


client = TestClient(app)


def test_additional_properties_post():
    response = client.post("/foo", json={"items": {"foo": 1, "bar": 2}})

from fastapi import FastAPI, Response
from fastapi.responses import JSONResponse
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class JsonApiResponse(JSONResponse):
    media_type = "application/vnd.api+json"


class Error(BaseModel):
    status: str
    title: str


class JsonApiError(BaseModel):
    errors: list[Error]


@app.get(
    "/a",

from fastapi import Depends, FastAPI, Security
from fastapi.security.open_id_connect_url import OpenIdConnect
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()

oid = OpenIdConnect(
    openIdConnectUrl="/openid", description="OpenIdConnect security scheme"
)


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str = Security(oid)):

/// warning | 注意

これらは今のあなたにとって重要でない場合は省略しても良い技術的な詳細です。

///

`RequestValidationError`はPydanticの<a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a>のサブクラスです。

**FastAPI** は`response_model`でPydanticモデルを使用していて、データにエラーがあった場合、ログにエラーが表示されるようにこれを使用しています。

from typing import Annotated, Union

from fastapi import FastAPI, Form
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class UserForm(BaseModel):
    name: str
    email: str


class CompanyForm(BaseModel):
    company_name: str
    industry: str


@app.post("/form-union/")
def post_union_form(data: Annotated[Union[UserForm, CompanyForm], Form()]):