Using Pre_delete Signal in django

Question

In my app I want to keep a track of all the questions that are being deleted. And so I have created a class(table) as such in my models file.

class Deleted(models.Model):
question = models.IntegerField(null=True, blank=True)#id of question being deleted
user = models.IntegerField(null=True, blank=True)#id of user deleting the question
dt = models.DateTimeField(null=True, blank=True)#time question is deleted

When a user tries to delete a question This delete function is called:

def delete_questions(request, user, questions):
  for q in questions:
        q.delete()

My doubt is how can i make a pre_delete signal of django to populate the new table I have created.

~newbie trying hefty task~ Thanks in advance:)

Answer 1

You start off by defining the receiver you want to use:

def log_deleted_question(sender, instance, using, **kwargs):
    d = Deleted()
    d.question = instance.id
    d.dt = datetime.datetime.now() # consider using auto_now=True in your Deleted definition
    # not sure how you'd get the user via a signal, 
    # since it can happen from a number of places (like the command line)
    d.save()

Then define your receiver decorator:

from django.db.models.signals import pre_delete
from django.dispatch import receiver

@receiver(pre_delete, sender=Question, dispatch_uid='question_delete_log')

Add it altogether:

from django.db.models.signals import pre_delete
from django.dispatch import receiver

@receiver(pre_delete, sender=Question, dispatch_uid='question_delete_signal')
def log_deleted_question(sender, instance, using, **kwargs):
    d = Deleted()
    d.question = instance.id
    d.dt = datetime.datetime.now() 
    d.save()

You can put this function in your models.py file, as you know it'll be loaded and connected up correctly.

The problem though, is that you don't get the user requesting the delete. Since a delete can be triggered from the django api (command line, shell, etc), which doesn't have a request associated with it. For this reason, you might want to avoid using signals if it's absolutely critical that you store the user along with the delete.