DRF validation - returns error 500 when error in Model.clean

Question

I have the fields refundable and refundable_price in my model. I need to be sure that there is refundable_price not None in case refundable is True.

Since I want it everywhere, I've overridden SubOffer.clean method:

from django.core.exceptions import ValidationError

def save(self, **kwargs):
    self.full_clean()
    super().save(**kwargs)

def clean(self):
    super().clean()
    if self.refundable and self.refundable_price is None:
        raise ValidationError("V prípade refundovateľnej ponuky je nutné zadať sumu (je možné zadať aj 0)")

And I use ModelViewSet.

class SubOfferViewSet(ModelViewSet):
    serializer_class = SubOfferSerializer
    filterset_fields = {
        # 'approved_by': ['exact'],
        # 'approved_dt': ['gte', 'lte', 'gt', 'lt'],
    }

    def get_queryset(self):
        return SubOffer.objects.all()

The weird thing is that when I send POST to the ViewSet it returns 500 instead of JSON errors if there is an error in Suboffer.clean. Other errors work correctly.

It's the same when I use AJAX and when I use DRF API Viewer.

How is that possible and how to make it work properly?

Answer 1

A clean way that will handle all of your Validation errors (and any other errors you might want) is to have a custom EXCEPTION_HANDLER that converts the Django ValidationError to a DRF one.

See:

from django.core.exceptions import ValidationError as DjangoValidationError
from rest_framework.exceptions import ValidationError as DRFValidationError
from rest_framework.serializers import as_serializer_error
from rest_framework.views import exception_handler as drf_exception_handler


def exception_handler(exc, context):

    if isinstance(exc, DjangoValidationError):
        exc = DRFValidationError(as_serializer_error(exc))

    return drf_exception_handler(exc, context)


"""
In settings:

REST_FRAMEWORK = {
    'EXCEPTION_HANDLER': 'path.to_module.drf.exception_handler',
}
"""

Source: https://gist.github.com/twidi/9d55486c36b6a51bdcb05ce3a763e79f

A more in-depth example: https://github.com/HackSoftware/Django-Styleguide-Example/blob/9761c7592af553084e95bb5f8f9407a173aac66f/styleguide_example/api/exception_handlers.py