How to save a model without sending a signal?

Question

How can I save a model, such that signals arent sent. (post_save and pre_save)

Answer 1

As far as I'm aware there still isn't a 'nice' way to do this, but if you're open to exploring hacky solutions, then I'll add one to the mix.

If you look at the django model source code, specifically save_base() here and here, you'll see that the pre_save() and post_save() signals are both wrapped in a conditional:

if not meta.auto_created:
  // Emit signal

We can directly manipulate the meta options of a model or instance through the _meta API which means we're able to 'disable' the signals from firing by setting auto_created = True on the instance we want to save.

For example:

@receiver(post_save, sender=(MyModel))
def save_my_model(sender, instance=None, created=False, **kwargs):
    if created:
        # Modify the instance
        instance.task_id = task.task_hash

        # HACK: Prevent `post_save` signal from being called during save
        instance._meta.auto_created = True
        instance.save()
        instance._meta.auto_created = False

    elif instance.has_changed("schedule"):
        # Modify the instance
        instance.task_id = 'abc123'

        # HACK: Prevent `post_save` signal from being called during save
        instance._meta.auto_created = True
        instance.save()
        instance._meta.auto_created = False

The major caveat here is that this is undocumented behaviour and it could well change it future releases of django.