Instance.delete() cascade deletes related objects with null=True

[oremj]

Server model relation:

server_model = models.ForeignKey('ServerModel', blank=True, null=True)

a = System.objects.all()[0]
b = ServerModels.objects.all()[0]

b.delete()

Both b and a are deleted.

db.connection.queries:

 {'sql': u'SELECT `systems`.`id`, `systems`.`hostname`, `systems`.`serial`, `systems`.`operating_system_id`, `systems`.`server_model_id`, `systems`.`created_on`, `systems`.`updated_on`, `systems`.`oob_ip`, `systems`.`asset_tag`, `systems`.`notes`, `systems`.`licenses`, `systems`.`allocation_id`, `systems`.`system_rack_id`, `systems`.`rack_order`, `systems`.`switch_ports`, `systems`.`patch_panel_port`, `systems`.`oob_switch_port`, `systems`.`purchase_date`, `systems`.`purchase_price`, `systems`.`system_status_id`, `systems`.`change_password`, `systems`.`ram` FROM `systems` WHERE `systems`.`server_model_id` = 221 ',
 {'sql': u'UPDATE `systems` SET `server_model_id` = NULL WHERE `id` IN (1333)',
 {'sql': u'DELETE FROM `systems` WHERE `id` IN (1333)'},
 {'sql': u'DELETE FROM `server_models` WHERE `id` IN (221)'}]

I'm not seeing this problem on 1.1, but I am seeing it on 1.1.1 and later.

[oremj]

Nevermind, this also happens on 1.1.

[Alexander Schepanovski]

Having the same problem with:

class Blog(models.Model):
    ...
    last_comment = models.ForeignKey('BlogComment', blank = True, null = True, editable = False)

class BlogComment(CommonComment):
    blog = models.ForeignKey(Blog)

When deleting last comment the whole blog is deleted. Django should be able to behave in 'on delete set null' style.
Having this on 1.1

[Karen Tracey]

More options for delete behavior is the subject of #7539. Right now Django just does CASCADE. If that isn't what you want there are ways to get around it, see for example: ​http://stackoverflow.com/questions/1006135/how-do-i-create-a-django-model-with-foreignkeys-which-does-not-cascade-deletes-to