Django — Signals

What are Signals?

Signals allow certain senders to notify a set of receivers when some action has taken place.

Built-in Signals

Signal	Sender	Description
pre_save	Model	Before save
post_save	Model	After save
pre_delete	Model	Before delete
post_delete	Model	After delete
m2m_changed	ManyToMany	M2M field changed

Basic Signal

# blog/signals.py
from django.db.models.signals import post_save
from django.dispatch import receiver
from django.contrib.auth.models import User

@receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
    if created:
        Profile.objects.create(user=instance)

Connect Signals

# blog/apps.py
class BlogConfig(AppConfig):
    default_auto_field = 'django.db.models.BigAutoField'
    name = 'blog'
    
    def ready(self):
        import blog.signals

Custom Signals

from django.dispatch import Signal

order_completed = Signal()

# Send signal
order_completed.send(sender=Order, order=order)

# Receive signal
@receiver(order_completed)
def send_confirmation(sender, order, **kwargs):
    send_mail('Order confirmed', 'Your order is ready', ...)

Mini Practice

1. Create a post_save signal
2. Connect signals in apps.py
3. Create a custom signal
4. Use signals for auditing

Up Next

Continue with Testing — writing tests in Django.