Imagine scenario when i want to explicitly mark a field that model constraint should raise ValidationError for:
class CustomUniqueConstraint(UniqueConstraint):
def validate(self, *args, **kwargs):
try:
value = super().validate(*args, **kwargs)
except ValidationError as e:
raise ValidationError(
{
'email': e,
}
)
return value
class AbstractUser(django.contrib.auth.models.AbstractUser):
class Meta:
abstract = True
constraints = [
CustomUniqueConstraint(
Lower("email"),
name="%(app_label)s_%(class)s_email_unique",
)
]
This wont work because:
1425, in validate_constraints
if e.code == "unique" and len(constraint.fields) == 1:
^^^^^^
AttributeError: 'ValidationError' object has no attribute 'code'
Maybe all unique constraints should allow raising validation error for specific field like ?
from django.core.exceptions import ValidationError
from django.db import models
class ViolationFieldNameMixin:
"""
Mixin for BaseConstraint subclasses that builds custom
ValidationError message for the `violation_field_name`.
By this way we can bind the error to the field that caused it.
This is useful in ModelForms where we can display the error
message next to the field and also avoid displaying unique
constraint violation error messages more than once for the same field.
"""
def __init__(self, *args, **kwargs):
self.violation_field_name = kwargs.pop("violation_field_name", None)
self.violation_code = kwargs.pop("violation_code", None)
super().__init__(*args, **kwargs)
def validate(self, *args, **kwargs):
try:
value = super().validate(*args, **kwargs)
except ValidationError as e:
e.code = self.violation_code
# Create a new ValidationError with the violation_field_name attribute as the key
e = ValidationError({self.violation_field_name: e})
# Set the error code to None
# See https://code.djangoproject.com/ticket/34319#ticket
e.code = self.violation_code
raise e
return value
def deconstruct(self):
path, args, kwargs = super().deconstruct()
kwargs["violation_field_name"] = self.violation_field_name
kwargs["violation_code"] = self.violation_code
return path, args, kwargs
def __eq__(self, other):
return (
super().__eq__(other)
and self.violation_field_name == getattr(other, "violation_field_name", None)
and self.violation_code == getattr(other, "violation_code", None)
)
class UniqueConstraint(ViolationFieldNameMixin, models.UniqueConstraint):
...
Replying to Mateusz Kurowski:
This is a regression in 667105877e6723c6985399803a364848891513cc, that we should fix.
I don't think that adding extra arguments is a step forward here, we should be able to recognized violated fields by inspecting
expression, see #34007.