[Django]-Django post_save preventing recursion without overriding model save()

you can use update instead of save in the signal handler

queryset.filter(pk=instance.pk).update(....)

Don’t disconnect signals. If any new model of the same type is generated while the signal is disconnected the handler function won’t be fired. Signals are global across Django and several requests can be running concurrently, making some fail while others run their post_save handler.

I think creating a save_without_signals() method on the model is more explicit:

class MyModel()
    def __init__():
        # Call super here.
        self._disable_signals = False

    def save_without_signals(self):
        """
        This allows for updating the model from code running inside post_save()
        signals without going into an infinite loop:
        """
        self._disable_signals = True
        self.save()
        self._disable_signals = False

def my_model_post_save(sender, instance, *args, **kwargs):
    if not instance._disable_signals:
        # Execute the code here.

How about disconnecting then reconnecting the signal within your post_save function:

def my_post_save_handler(sender, instance, **kwargs):
    post_save.disconnect(my_post_save_handler, sender=sender)
    instance.do_stuff()
    instance.save()
    post_save.connect(my_post_save_handler, sender=sender)
post_save.connect(my_post_save_handler, sender=Order)

You should use queryset.update() instead of Model.save() but you need to take care of something else:

It’s important to note that when you use it, if you want to use the new object you should get his object again, because it will not change the self object, for example:

>>> MyModel.objects.create(pk=1, text='')
>>> el = MyModel.objects.get(pk=1)
>>> queryset.filter(pk=1).update(text='Updated')
>>> print el.text
>>> ''

So, if you want to use the new object you should do again:

>>> MyModel.objects.create(pk=1, text='')
>>> el = MyModel.objects.get(pk=1)
>>> queryset.filter(pk=1).update(text='Updated')
>>> el = MyModel.objects.get(pk=1) # Do it again
>>> print el.text
>>> 'Updated'

You could also check the raw argument in post_save and then call save_baseinstead of save.

the Model’s .objects.update() method bypasses the post_save signal

Try this something like this:

from django.db import models
from django.db.models.signals import post_save


class MyModel(models.Model):

    name = models.CharField(max_length=200)
    num_saves = models.PositiveSmallIntegerField(default=0)

    @classmethod
    def post_save(cls, sender, instance, created, *args, **kwargs):
        MyModel.objects.filter(id=instance.id).update(save_counter=instance.save_counter + 1)

post_save.connect(MyModel.post_save, sender=MyModel)

In this example, an object has a name and each time .save() is called, the .num_saves property is incremented, but without recursion.

Check this out…

Each signal has it’s own benefits as you can read about in the docs here but I wanted to share a couple things to keep in mind with the pre_save and post_save signals.

• Both are called every time .save() on a model is called. In other words, if you save the model instance, the signals are sent.

• running save() on the instance within a post_save can often create a never ending loop and therefore cause a max recursion depth exceeded error — only if you don’t use .save() correctly.

• pre_save is great for changing just instance data because you do not have to call save() ever which eliminates the possibility for above. The reason you don’t have to call save() is because a pre_save signal literally means right before being saved.

• Signals can call other signals and or run delayed tasks (for Celery) which can be huge for usability.

Source: https://www.codingforentrepreneurs.com/blog/post-save-vs-pre-save-vs-override-save-method/

Regards!!

In post_save singal in django for avoiding recursion ‘if created’ check is required

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

@receiver(post_save, sender=DemoModel)
def _post_save_receiver(sender,instance,created, **kwargs):
    if created:            
       print('hi..')
       instance.save()

I was using the save_without_signals() method by @Rune Kaagaard until i updated my Django to 4.1. On Django 4.1 this method started raising an Integrity error on the database that gave me 4 days of headaches and i couldn’t fix it.

So i started to use the queryset.update() method and it worked like a charm. It doesn’t trigger the pre_save() neither post_save() and you don’t need to override the save() method of your model. 1 line of code.

@receiver(pre_save, sender=Your_model)
def any_name(sender, instance, **kwargs):
    Your_model.objects.filter(pk=instance.pk).update(model_attribute=any_value)