FastAPI接口未用Model定义Body参数，SwaggerUI无法生成对应文档

首先要注意：GET请求规范上不应该携带请求体，FastAPI虽然支持，但SwaggerUI遵循HTTP标准，会对GET请求的请求体参数渲染异常。这很可能是你遇到问题的核心原因，建议先将接口方法改为POST。

在此基础上，通过以下两种方式优化参数定义，让SwaggerUI正确识别参数的描述、必填/可选状态，无需使用Pydantic Model：

1. 显式指定Body参数的required属性 #

即使FastAPI会自动根据参数是否有默认值判断必填性，显式设置required参数可以让SwaggerUI更准确地识别状态，同时保留描述信息：

from fastapi import Body, Header, Request, APIRouter
from typing import Annotated, List

vault_router = APIRouter()

@vault_router.post('/secret')
def get_secret(
    token: Annotated[str, Header(description="Requires token to be sent in headers as access_token")],
    request: Request,
    path: Annotated[str, Body(description="key-vault path which needs to be accessed", required=True)], 
    keys: Annotated[List | None, Body(description="list of keys to fetch from the specified path", required=False)] = None
):
    # code goes here
    return {"path": path, "keys": keys}

2. 结合Pydantic Field增强元数据 #

使用Field定义参数的元数据（如描述），再嵌套到Body中，能让SwaggerUI更精准地解析参数信息：

from fastapi import Body, Header, Request, APIRouter
from pydantic import Field
from typing import Annotated, List

vault_router = APIRouter()

@vault_router.post('/secret')
def get_secret(
    token: Annotated[str, Header(description="Requires token to be sent in headers as access_token")],
    request: Request,
    path: Annotated[str, Body(Field(description="key-vault path which needs to be accessed"))], 
    keys: Annotated[List | None, Body(Field(description="list of keys to fetch from the specified path"))] = None
):
    # code goes here
    return {"path": path, "keys": keys}

修改后，SwaggerUI会正确展示每个请求体参数的描述、必填（path无默认值）和可选（keys默认值为None）状态，与Redoc的表现一致。

内容的提问来源于stack exchange，提问作者Ritik Saxena