Django Signals Deep Dive

Django Signals Best Practices

# Connect in apps.py ready() - not at module level
class BlogConfig(AppConfig):
    name = "blog"
    def ready(self):
        import blog.signals

# blog/signals.py
from django.db.models.signals import post_save, pre_delete
from django.dispatch import receiver, Signal

post_published = Signal()  # custom signal

@receiver(post_save, sender=Post)
def on_post_saved(sender, instance, created, **kwargs):
    if created:
        instance.author.profile.increment_post_count()

@receiver(post_published)
def notify_followers(sender, post, **kwargs):
    msg = post.author.name + " published: " + post.title
    for follower in post.author.followers.all():
        Notification.objects.create(recipient=follower, message=msg)

@receiver(pre_delete, sender=Post)
def cleanup_files(sender, instance, **kwargs):
    if instance.image:
        instance.image.delete(save=False)

# Fire custom signal
post_published.send(sender=Post, post=instance)