Signals

Wagtail’s PageRevision and Page implement Signals from django.dispatch. Signals are useful for creating side-effects from page publish/unpublish events.

For example, you could use signals to send publish notifications to a messaging service, or POST messages to another app that’s consuming the API, such as a static site generator.

page_published

This signal is emitted from a PageRevision when a revision is set to published.

sender:The page class.
instance:The specific Page instance.
revision:The PageRevision that was published.
kwargs:Any other arguments passed to page_published.send().

To listen to a signal, implement page_published.connect(receiver, sender, **kwargs). Here’s a simple example showing how you might notify your team when something is published:

from wagtail.core.signals import page_published
import requests


# Let everyone know when a new page is published
def send_to_slack(sender, **kwargs):
    instance = kwargs['instance']
    url = 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
    values = {
        "text" : "%s was published by %s " % (instance.title, instance.owner.username),
        "channel": "#publish-notifications",
        "username": "the squid of content",
        "icon_emoji": ":octopus:"
    }

    response = requests.post(url, values)

# Register a receiver
page_published.connect(send_to_slack)

Receiving specific model events

Sometimes you’re not interested in receiving signals for every model, or you want to handle signals for specific models in different ways. For instance, you may wish to do something when a new blog post is published:

from wagtail.core.signals import page_published
from mysite.models import BlogPostPage

# Do something clever for each model type
def receiver(sender, **kwargs):
    # Do something with blog posts
    pass

# Register listeners for each page model class
page_published.connect(receiver, sender=BlogPostPage)

Wagtail provides access to a list of registered page types through the get_page_models() function in wagtail.core.models.

Read the Django documentation for more information about specifying senders.

page_unpublished

This signal is emitted from a Page when the page is unpublished.

sender:The page class.
instance:The specific Page instance.
kwargs:Any other arguments passed to page_unpublished.send()

pre_page_move and post_page_move

New in version 2.10.

These signals are emitted from a Page immediately before and after it is moved.

Subscribe to pre_page_move if you need to know values BEFORE any database changes are applied. For example: Getting the page’s previous URL, or that of its descendants.

Subscribe to post_page_move if you need to know values AFTER database changes have been applied. For example: Getting the page’s new URL, or that of its descendants.

The following arguments are emitted for both signals:

sender:The page class.
instance:The specific Page instance.
parent_page_before:
 The parent page of instance before moving.
parent_page_after:
 The parent page of instance after moving.
url_path_before:
 The value of instance.url_path before moving.
url_path_after:The value of instance.url_path after moving.
kwargs:Any other arguments passed to pre_page_move.send() or post_page_move.send().

Distinguishing between a ‘move’ and a ‘reorder’

The signal can be emitted as a result of a page being moved to a different section (a ‘move’), or as a result of a page being moved to a different position within the same section (a ‘reorder’). Knowing the difference between the two can be particularly useful, because only a ‘move’ affects a page’s URL (and that of its descendants), whereas a ‘reorder’ only affects the natural page order; which is probably less impactful.

The best way to distinguish between a ‘move’ and ‘reorder’ is to compare the url_path_before and url_path_after values. For example:

from wagtail.core.signals import pre_page_move
from wagtail.contrib.frontend_cache.utils import purge_page_from_cache

# Clear a page's old URLs from the cache when it moves to a different section
def clear_page_url_from_cache_on_move(sender, **kwargs):

    if kwargs['url_path_before'] == kwargs['url_path_after']:
        # No URLs are changing :) nothing to do here!
        return

    # The page is moving to a new section (possibly even a new site)
    # so clear old URL(s) from the cache
    purge_page_from_cache(kwargs['instance'])

# Register a receiver
pre_page_move.connect(clear_old_page_urls_from_cache)