django-xvalidate allows you to declare cross-field validators within a Django model.
As an example, consider a Django model named Event.
from django.db import models
class Event(models.Model):
title = models.CharField(max_length=255)
start_date = models.DateField()
end_date = models.DateField()django-xvalidate allows you to declare that the start date precedes the end date as follows:
from django.db import models
from xvalidate import XValidatedModel, XLe
class Event(XValidatedModel, models.Model):
title = models.CharField(max_length=255)
start_date = models.DateField()
end_date = models.DateField()
class XVMeta(XValidatedModel.XVMeta):
spec = [
XLe('start_date', 'end_date').message(
'The start date should precede the end date')
]XValidatedModel ensures that this specification is maintained
invoking Event.clean() and raises ValidationError as
appropriate.
django-xvalidate allows you to specify how to validate your model instances
in a more declarative manner than writing imperative code within your
clean() methods. Without django-xvalidate you would have to
implement the above example as
def clean(self):
super(Event, self).clean()
if (self.start_date is not None) and (self.end_date is not None):
if (self.end_date < self.start_date):
raise ValidationError('The start date should precede the end date')With a more declarative format we have the option at some point in the future to automate the creation of test data that passes (or fails) validation.
django-xvalidate comes some operator overloading that brings syntactic sugar to your declarations making them very easy to read. For instance, you could specify:
((XF('end_date') - 'start_date') > datetime.timedelta(days=4)).message(
'Event should last at least 5 days'
)django-xvalidate also allows the use of Django's double-underscore (__) syntax to dereference related objects, enabling succinct definitions such as the following
(XF('registration_date') <= 'event__end_date').message(
'Must register before the event ends')