id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
35073	models.SET's callable is called when there are no objects to update.	Fabio Sangiovanni	bcail	"Hello everybody.

With an upgrade from Django 4.1 to 4.2 (but also verified in Django 5.0), I've noticed a change in behavior with how on_delete=models.SET is handled.
Given the following models:


{{{
from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=32)

    def __str__(self):
        return self.name


def get_default_person():
    return Person.objects.get_or_create(name=""ghost"")[0]


class Pet(models.Model):
    name = models.CharField(max_length=32)
    person = models.ForeignKey(Person, related_name=""pets"", on_delete=models.SET(get_default_person))

    def __str__(self):
        return self.name

}}}

I can see what follows in Django 4.2+ (in ./manage.py shell):

{{{
>>> from pets.models import Person, Pet
>>> Person.objects.all()
<QuerySet []>
>>> Pet.objects.all()
<QuerySet []>
>>> Person.objects.create(name=""johndoe"")
<Person: johndoe>
>>> Person.objects.all()
<QuerySet [<Person: johndoe>]>
>>> Person.objects.all().delete()
(1, {'pets.Person': 1})
>>> Person.objects.all()
<QuerySet [<Person: ghost>]>
}}}

What is strange to me is that the ""ghost"" Person instance is created upon deletion of the ""johndoe"" instance, even if there are no Pets with a ForeignKey to ""johndoe"".
Django 4.1 behaves differently (no ""ghost"" Person is created on deletion of other Person objects).

Is this an intended change? I couldn't find any documentation of this in the release notes.

Thanks so much for your help.

Fabio
"	Bug	closed	Database layer (models, ORM)	4.2	Normal	fixed		Simon Charette bcail	Ready for checkin	1	0	0	0	0	0