[QUESTION] Handling Exception Response format

Hello. I want to change the validation error response and make it inside app object.

I’ve found this example:

@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(), "body": exc.body}),
    )

But can’t understand how to add this function to app object without decorator:

app = FastAPI(
    title='Bla API',
    description='Bla description',
    APIRoute('/api', api.toggle, methods=['POST'],
             description='Switch interface state',
             response_description='Interface successfully switched',
             response_class=JSONResponse,
             response_model=api.Success,
             responses={**api.post_responses},
             ),
...

[horseinthesky]

@MacMacky Ok. Thanks again for your help.

[davemaharshi7]

may be you can try this:

"""For managing validation error for complete application."""
from typing import Union
from fastapi.exceptions import RequestValidationError
from fastapi.openapi.constants import REF_PREFIX
from fastapi.openapi.utils import validation_error_response_definition
from pydantic import ValidationError
from starlette.requests import Request
from starlette.responses import JSONResponse
from starlette.status import HTTP_422_UNPROCESSABLE_ENTITY


async def http422_error_handler(
    _: Request, exc: Union[RequestValidationError, ValidationError],
) -> JSONResponse:
    """To handle unprocessable request(HTTP_422) and log accordingly to file.

    Args:
        _ (Request): Request object containing metadata about Request
        exc (Union[RequestValidationError, ValidationError]): to handle RequestValidationError,
            ValidationError

    Returns:
        JSONResponse: JSON response with required status code.
    """
    return JSONResponse(
        {"error": exc.errors()}, status_code=HTTP_422_UNPROCESSABLE_ENTITY,
    )


validation_error_response_definition["properties"] = {
    "errors": {
        "title": "Errors",
        "type": "array",
        "items": {"$ref": "{0}ValidationError".format(REF_PREFIX)},
    },
}

And in main.py

app.add_exception_handler(RequestValidationError, http422_error_handler)