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Code Issues 32 Releases Wiki Activity

[4.1.x] Fixed #30801 -- Improved guidance for making good use of signals.

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Backport of 71e9694856 from main
This commit is contained in:
Joseph Victor Zammit
2022-10-22 18:52:53 +02:00
committed by Carlton Gibson
parent e8ea852f07
commit 018311d481
2 changed files with 35 additions and 23 deletions
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44
docs/topics/signals.txt
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@@ -11,38 +11,34 @@ allow certain *senders* to notify a set of *receivers* that some action has
taken place. They're especially useful when many pieces of code may be
interested in the same events.
Django provides a :doc:`set of built-in signals </ref/signals>` that let user
code get notified by Django itself of certain actions. These include some useful
notifications:
For example, a third-party app can register to be notified of settings
changes::
* :data:`django.db.models.signals.pre_save` &
:data:`django.db.models.signals.post_save`
from django.apps import AppConfig
from django.core.signals import setting_changed
Sent before or after a model's :meth:`~django.db.models.Model.save` method
is called.
def my_callback(sender, **kwargs):
print("Setting changed!")
* :data:`django.db.models.signals.pre_delete` &
:data:`django.db.models.signals.post_delete`
class MyAppConfig(AppConfig):
...
Sent before or after a model's :meth:`~django.db.models.Model.delete`
method or queryset's :meth:`~django.db.models.query.QuerySet.delete`
method is called.
def ready(self):
setting_changed.connect(my_callback)
* :data:`django.db.models.signals.m2m_changed`
Django's :doc:`built-in signals </ref/signals>` let user code get notified of
certain actions.
Sent when a :class:`~django.db.models.ManyToManyField` on a model is changed.
You can also define and send your own custom signals. See
:ref:`defining-and-sending-signals` below.
* :data:`django.core.signals.request_started` &
:data:`django.core.signals.request_finished`
.. warning::
Sent when Django starts or finishes an HTTP request.
Signals give the appearance of loose coupling, but they can quickly lead to
code that is hard to understand, adjust and debug.
See the :doc:`built-in signal documentation </ref/signals>` for a complete list,
and a complete explanation of each signal.
You can also `define and send your own custom signals`_; see below.
.. _define and send your own custom signals: `defining and sending signals`_
Where possible you should opt for directly calling the handling code,
rather than dispatching via a signal.
Listening to signals
====================
@@ -218,6 +214,8 @@ bound to the signal once for each unique ``dispatch_uid`` value::
request_finished.connect(my_callback, dispatch_uid="my_unique_identifier")
.. _defining-and-sending-signals:
Defining and sending signals
============================