Django has done a lot right with their framework and signals is one of the best parts. Signals help decoupled applications get notified when other actions occur in the framework.
Out of the box Django gives you several signals that are incredibly useful. You have the ability to do things pre and post save, init, delete, or even when a request is being processed. So lets get away from the concepts and demonstrate how these are used. Say we’ve got a blog
class Post(models.Model): title = models.CharField(_('title'), max_length=255) body = models.TextField(_('body')) created = models.DateTimeField(auto_now_add=True)
So somehow you want to notify one of the many blog-pinging services we’ve made a new post, rebuild the most recent posts cache, and tweet about it. Well with signals you have the ability to do all of this without having to add any methods to the Post class.
import twitter from django.core.cache import cache from django.db.models.signals import post_save from django.conf import settings def posted_blog(sender, created=None, instance=None, **kwargs): ''' Listens for a blog post to save and alerts some services. ''' if (created and instance is not None): tweet = 'New blog post! %s' instance.title t = twitter.PostUpdate(settings.TWITTER_USER, settings.TWITTER_PASSWD, tweet) cache.set(instance.cache_key, instance, 60*5) # send pingbacks # ... # whatever else else: cache.delete(instance.cache_key) post_save.connect(posted_blog, sender=Post)
There we go, by defining that function and using the post_init signal to connect the function to the Post model and execute it after it has been saved. The best part about it? It’s all built in.
Timblr fails at comments, so just @reply @notzach.
p.s. chances are this code is broken, examples fool.5 years ago