Django: How to create a signal for deleting a instance of pre_save signal?

Question

I have the following pre_save signal in my models:

@receiver(pre_save, sender=Purchase)
def user_created_purchase_cgst(sender,instance,*args,**kwargs):
    c = Journal.objects.filter(user=instance.user, company=instance.company).count() + 1
    if instance.cgst_alltotal != None and instance.cgst_alltotal != 0:
        Journal.objects.update_or_create(
            user=instance.user,
            company=instance.company,
            by=ledger1.objects.filter(user=instance.user,company=instance.company,name__icontains='CGST').first(),
            to=instance.party_ac,
            defaults={
                'counter' : c,
                'date': instance.date,
                'voucher_id' : instance.id,
                'voucher_type' : "Journal",
                'debit': instance.cgst_alltotal,
                'credit': instance.cgst_alltotal}
            )

I want to create another signal similar to the above that when the sender is deleted then the sender instance will also get deleted.

i.e when a Purchase object is deleted then the corresponding Journal object which is created by the pre_save signal will get deleted.

Any idea anyone how to perform this?

Thank you

Your question is confusing. There is nothing being deleted on your code. What exactly are you trying to do. — Stargazer, Mar 28 '19 at 11:35
Just read my question I said I want to create another signal for deleting the instance whenever the sender is being deleted — Niladry Kar, Mar 28 '19 at 11:36
Why don't you just use django's `pre_delete` or `post_delete` built-in signals? https://docs.djangoproject.com/en/2.1/ref/signals/#pre-delete — Stargazer, Mar 28 '19 at 11:46
I am actually new to django and have not used much of `pre_delete` signal...So I was wondering how it should be done — Niladry Kar, Mar 28 '19 at 11:48

Stargazer · Accepted Answer · 2019-03-28T11:59:43.550

3

It will be something like this:

@receiver(pre_delete, sender=Purchase)
def delete_related_journal(sender, instance, **kwargs):
    journal = instance.journal # instance is your Purchase instance that is
    # about to be deleted
    journal.delete()

But be aware, if the Journal purchase Foreign Key is setted to on_delete=models.CASCADE, you don't have to do this at all. So, if CASCADE is not setted, you might want to do it instead using a signal.

class JournalModel(models.Model):
    # Your other fields here
    purchase = models.ForeignKey(Purchase, on_delete=models.CASCADE)

Django: How to create a signal for deleting a instance of pre_save signal?

1 Answers1