I want my ModelForm error handler to show validation errors from the save() method just like they do in the clean() method – i.e. as a warning on the admin form, instead of generating a 500 page.

The code flow is as follows, in admin.py:

class XForm(ModelForm):
    def save(self, **kwargs):
        super().save(**kwargs)
        try:
            self.instance.update_more_stuff_based_on_extra_fields_in_the_form()
        except IntegrityError:
            raise ValidationError(_("Earth to Monty Python."))
        return self.instance


class XAdmin(admin.ModelAdmin):
    form = XForm

admin.site.register(X, XAdmin)

This results in a debugger’s 500 page when the validation error is triggered, not the preferred admin warning.

Note: The following question addresses the similar problem of raising a validation error within the model’s save method. Here we want to raise the error in the model form’s save method.