向最终用户显示 FastAPI 验证错误

Question

我正在寻找一些库或代码示例来将 FastAPI 验证消息格式化为人类可读的格式。例如这个端点：

@app.get("/")
async def hello(name: str):
    return {"hello": name}

如果我们错过name查询参数，将产生下一个 json 输出：

{ 
    "detail":[ 
        { 
            "loc":[ 
                "query",
                "name"
            ],
            "msg":"field required",
            "type":"value_error.missing"
        }
    ]
}

所以我的问题是，如何：

1. 将其转换为“需要名称字段”（针对各种可能的错误）以显示在吐司中。
2. 使用它来显示表单验证消息
3. 如果可能的话，从 api 描述中自己生成表单

Answer 1

I reached here with a similar question - and I ended up handling the RequestValidationError to give back a response where every field is an array of the issues with that field. The response to your request would become (with a status_code=400)

    {
        "detail": "Invalid request",
        "errors": {"name": ["field required"]}
    }

that's quite handy to manage on the frontend for snackbar notifications and flexible enough.

Here's the handler

from collections import defaultdict

from fastapi import status
from fastapi.encoders import jsonable_encoder
from fastapi.responses import JSONResponse


@app.exception_handler(RequestValidationError)
async def custom_form_validation_error(request, exc):
    reformatted_message = defaultdict(list)
    for pydantic_error in exc.errors():
        loc, msg = pydantic_error["loc"], pydantic_error["msg"]
        filtered_loc = loc[1:] if loc[0] in ("body", "query", "path") else loc
        field_string = ".".join(filtered_loc)  # nested fields with dot-notation
        reformatted_message[field_string].append(msg)

    return JSONResponse(
        status_code=status.HTTP_400_BAD_REQUEST,
        content=jsonable_encoder(
            {"detail": "Invalid request", "errors": reformatted_message}
        ),
    )

Answer 2

FastAPI 具有出色的异常处理，因此您可以通过多种方式自定义异常。

您可以引发 HTTPException，HTTPException 是一个普通的 Python 异常，带有与 API 相关的附加数据。但是你不能返回它你需要提高它，因为它是一个 Python 异常

from fastapi import HTTPException
...
@app.get("/")
async def hello(name: str):
    if not name:
        raise HTTPException(status_code=404, detail="Name field is required")
    return {"Hello": name}

通过添加name: str为查询参数，它会自动成为必需的，因此您需要添加Optional

from typing import Optional
...
@app.get("/")
async def hello(name: Optional[str] = None):
    error = {"Error": "Name field is required"}
    if name:
        return {"Hello": name}
    return error

$ curl 127.0.0.1:8000/?name=imbolc
{"Hello":"imbolc"}
...
$ curl 127.0.0.1:8000
{"Error":"Name field is required"}

但在您的情况下，我认为这是处理 FastAPI 中错误的最佳方法，覆盖了validation_exception_handler：

from fastapi import FastAPI, Request, status
from fastapi.encoders import jsonable_encoder
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
...
@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
    return JSONResponse(
        status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
        content=jsonable_encoder({"detail": exc.errors(), "Error": "Name field is missing"}),
    )
...
@app.get("/")
async def hello(name: str):
    return {"hello": name}

你会得到这样的回应：

$ curl 127.0.0.1:8000

 {
   "detail":[
      {
         "loc":[
            "query",
            "name"
         ],
         "msg":"field required",
         "type":"value_error.missing"
      }
   ],
   "Error":"Name field is missing"
}

content如果您愿意，您可以自定义您的然而：

{
"Error":"Name field is missing",
   "Customize":{
      "This":"content",
      "Also you can":"make it simpler"
   }
}