Cancel saving model when using pre_save in django

Question

I have a model:

class A(models.Model):     number = models.IntegerField() 

But when I call A.save(), I want to ensure that number is a prime (or other conditions), or the save instruction should be cancelled.

So how can I cancel the save instruction in the pre_save signal receiver?

@receiver(pre_save, sender=A) def save_only_for_prime_number(sender, instance, *args, **kwargs):     # how can I cancel the save here? 

Answer 1

See my another answer: https://stackoverflow.com/a/32431937/2544762

This case is normal, if we just want to prevent the save, throw an exception:

from django.db.models.signals import pre_save, post_save  @receiver(pre_save) def pre_save_handler(sender, instance, *args, **kwargs):     # some case     if case_error:         raise Exception('OMG') 

Answer 2

I'm not sure you can cancel the save only using the pre_save signal. But you can easily achieve this by overriding the save method:

def save(self):     if some_condition:         super(A, self).save()     else:        return   # cancel the save 

As mentioned by @Raptor, the caller won't know if the save was successful or not. If this is a requirement for you, take look at the other answer which forces the caller to deal with the "non-saving" case.