Django one-off on_save callbacks

utils.py

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


def on_save(obj: models.Model, callback, on_commit=False):
    """
    Attaches a one-off callback that's triggered after a Django model instance is
    saved. Optionally makes use of transaction.on_commit to defer until any wrapping
    transaction has also committed.
    
    This lets us build up a queue of side-effects to get triggered after some changes
    are saved to the database, but crucially in a way such that the side-effects aren't
    triggered if the save fails for some reason.
    
    Usage:
    
    on_save(my_instance, lambda: track_event('Something happened'))
    on_save(my_instance, lambda: track_event('Something happened'), on_commit=True)
    
    """

    def receiver(sender, instance, using, **kwargs):
        if instance == obj:
            if on_commit:
                transaction.on_commit(callback, using=using)
            else:
                callback()
            post_save.disconnect(receiver)

    post_save.connect(receiver, sender=type(obj))