如何创建可接受File/Form或JSON请求体的FastAPI端点？

你可以通过两种方式实现需求：一是检测请求的Content-Type头来分别处理不同类型的请求体，二是通过依赖项统一解析逻辑。以下是具体实现方案：

方案一：检测请求类型并分别处理 #

通过Request对象获取请求头中的Content-Type，判断当前请求是JSON还是multipart/form-data，再对应解析数据：

from fastapi import FastAPI, Request, Form, File, UploadFile
from pydantic import BaseModel
from typing import Optional

app = FastAPI()

class Item(BaseModel):
    name: str
    description: Optional[str] = None

@app.post("/process")
async def process_request(
    request: Request,
    file: Optional[UploadFile] = File(None),
    name: Optional[str] = Form(None),
    description: Optional[str] = Form(None)
):
    content_type = request.headers.get("Content-Type")
    if not content_type:
        return {"error": "Missing Content-Type header"}
    
    if "application/json" in content_type:
        # 解析JSON请求体
        json_data = await request.json()
        item = Item(**json_data)
    elif "multipart/form-data" in content_type:
        # 解析form-data表单数据
        if not name:
            return {"error": "Missing 'name' field in form-data"}
        item = Item(name=name, description=description)
        # 处理上传的文件（如果有）
        file_info = file.filename if file else None
    else:
        return {"error": "Unsupported Content-Type. Use application/json or multipart/form-data"}
    
    response = {"received_item": item.dict()}
    if "file_info" in locals():
        response["uploaded_file"] = file_info
    return response

方案二：用依赖项统一解析逻辑 #

将请求解析逻辑封装为依赖函数，让端点代码更简洁：

from fastapi import FastAPI, Depends, Request, Form, File, UploadFile
from pydantic import BaseModel
from typing import Optional

app = FastAPI()

class Item(BaseModel):
    name: str
    description: Optional[str] = None

async def parse_request(request: Request, name: Optional[str] = Form(None), description: Optional[str] = Form(None)) -> Item:
    content_type = request.headers.get("Content-Type")
    if "application/json" in content_type:
        return Item(**await request.json())
    elif "multipart/form-data" in content_type:
        if not name:
            raise ValueError("'name' field is required in form-data")
        return Item(name=name, description=description)
    else:
        raise ValueError("Unsupported Content-Type")

@app.post("/process")
async def process_request(item: Item = Depends(parse_request), file: Optional[UploadFile] = File(None)):
    response = {"item": item.dict()}
    if file:
        response["uploaded_file"] = file.filename
    return response

注意事项 #

• 判断Content-Type时用包含判断（in），因为multipart/form-data请求通常会带boundary参数（如multipart/form-data; boundary=----WebKitFormBoundaryxxx）。
• 若form-data的字段名与JSON模型字段不一致，需在Form参数中做映射（比如Form(None, alias="form_field_name")）。
• JSON请求无法直接传递文件，文件上传仅支持multipart/form-data格式，因此File参数需设为可选。

内容的提问来源于stack exchange，提问作者STY