Signals
A list of all the signals that Django sends. All built-in signals are sent using the send()
method.
See also
See the documentation on the signal dispatcher for information regarding how to register for and receive signals.
The authentication framework sends signals when a user is logged in / out.
Model signals
The django.db.models.signals
module defines a set of signals sent by the model system.
Warning
Many of these signals are sent by various model methods like __init__()
or save()
that you can override in your own code.
If you override these methods on your model, you must call the parent class’ methods for this signals to be sent.
Note also that Django stores signal handlers as weak references by default, so if your handler is a local function, it may be garbage collected. To prevent this, pass weak=False
when you call the signal’s connect()
.
Note
Model signals sender
model can be lazily referenced when connecting a receiver by specifying its full application label. For example, an Answer
model defined in the polls
application could be referenced as 'polls.Answer'
. This sort of reference can be quite handy when dealing with circular import dependencies and swappable models.
pre_init
-
django.db.models.signals.pre_init
Whenever you instantiate a Django model, this signal is sent at the beginning of the model’s __init__()
method.
Arguments sent with this signal:
-
sender
- The model class that just had an instance created.
-
args
- A list of positional arguments passed to
__init__()
: -
kwargs
- A dictionary of keyword arguments passed to
__init__()
:
For example, the tutorial has this line:
p = Poll(question="What's up?", pub_date=datetime.now())
The arguments sent to a pre_init
handler would be:
Argument | Value |
---|---|
sender |
Poll (the class itself) |
args |
[] (an empty list because there were no positional arguments passed to __init__() .) |
kwargs | {'question': "What's up?", 'pub_date': datetime.now()} |
post_init
-
django.db.models.signals.post_init
Like pre_init, but this one is sent when the __init__()
method finishes.
Arguments sent with this signal:
-
sender
- As above: the model class that just had an instance created.
-
instance
- The actual instance of the model that’s just been created.
pre_save
-
django.db.models.signals.pre_save
This is sent at the beginning of a model’s save()
method.
Arguments sent with this signal:
-
sender
- The model class.
-
instance
- The actual instance being saved.
-
raw
- A boolean;
True
if the model is saved exactly as presented (i.e. when loading a fixture). One should not query/modify other records in the database as the database might not be in a consistent state yet. -
using
- The database alias being used.
-
update_fields
- The set of fields to update as passed to
Model.save()
, orNone
ifupdate_fields
wasn’t passed tosave()
.
post_save
-
django.db.models.signals.post_save
Like pre_save
, but sent at the end of the save()
method.
Arguments sent with this signal:
-
sender
- The model class.
-
instance
- The actual instance being saved.
-
created
- A boolean;
True
if a new record was created. -
raw
- A boolean;
True
if the model is saved exactly as presented (i.e. when loading a fixture). One should not query/modify other records in the database as the database might not be in a consistent state yet. -
using
- The database alias being used.
-
update_fields
- The set of fields to update as passed to
Model.save()
, orNone
ifupdate_fields
wasn’t passed tosave()
.
pre_delete
-
django.db.models.signals.pre_delete
Sent at the beginning of a model’s delete()
method and a queryset’s delete()
method.
Arguments sent with this signal:
-
sender
- The model class.
-
instance
- The actual instance being deleted.
-
using
- The database alias being used.
post_delete
-
django.db.models.signals.post_delete
Like pre_delete
, but sent at the end of a model’s delete()
method and a queryset’s delete()
method.
Arguments sent with this signal:
-
sender
- The model class.
-
instance
-
The actual instance being deleted.
Note that the object will no longer be in the database, so be very careful what you do with this instance.
-
using
- The database alias being used.
m2m_changed
-
django.db.models.signals.m2m_changed
Sent when a ManyToManyField
is changed on a model instance. Strictly speaking, this is not a model signal since it is sent by the ManyToManyField
, but since it complements the pre_save
/post_save
and pre_delete
/post_delete
when it comes to tracking changes to models, it is included here.
Arguments sent with this signal:
-
sender
- The intermediate model class describing the
ManyToManyField
. This class is automatically created when a many-to-many field is defined; you can access it using thethrough
attribute on the many-to-many field. -
instance
- The instance whose many-to-many relation is updated. This can be an instance of the
sender
, or of the class theManyToManyField
is related to. -
action
-
A string indicating the type of update that is done on the relation. This can be one of the following:
-
"pre_add"
- Sent before one or more objects are added to the relation.
-
"post_add"
- Sent after one or more objects are added to the relation.
-
"pre_remove"
- Sent before one or more objects are removed from the relation.
-
"post_remove"
- Sent after one or more objects are removed from the relation.
-
"pre_clear"
- Sent before the relation is cleared.
-
"post_clear"
- Sent after the relation is cleared.
-
-
reverse
- Indicates which side of the relation is updated (i.e., if it is the forward or reverse relation that is being modified).
-
model
- The class of the objects that are added to, removed from or cleared from the relation.
-
pk_set
-
For the
pre_add
,post_add
,pre_remove
andpost_remove
actions, this is a set of primary key values that have been added to or removed from the relation.For the
pre_clear
andpost_clear
actions, this isNone
. -
using
- The database alias being used.
For example, if a Pizza
can have multiple Topping
objects, modeled like this:
class Topping(models.Model): # ... pass class Pizza(models.Model): # ... toppings = models.ManyToManyField(Topping)
If we connected a handler like this:
from django.db.models.signals import m2m_changed def toppings_changed(sender, **kwargs): # Do something pass m2m_changed.connect(toppings_changed, sender=Pizza.toppings.through)
and then did something like this:
>>> p = Pizza.objects.create(...) >>> t = Topping.objects.create(...) >>> p.toppings.add(t)
the arguments sent to a m2m_changed
handler (toppings_changed
in the example above) would be:
Argument | Value |
---|---|
sender |
Pizza.toppings.through (the intermediate m2m class) |
instance |
p (the Pizza instance being modified) |
action |
"pre_add" (followed by a separate signal with "post_add" ) |
reverse |
False (Pizza contains the ManyToManyField , so this call modifies the forward relation) |
model |
Topping (the class of the objects added to the Pizza ) |
pk_set |
{t.id} (since only Topping t was added to the relation) |
using |
"default" (since the default router sends writes here) |
And if we would then do something like this:
>>> t.pizza_set.remove(p)
the arguments sent to a m2m_changed
handler would be:
Argument | Value |
---|---|
sender |
Pizza.toppings.through (the intermediate m2m class) |
instance |
t (the Topping instance being modified) |
action |
"pre_remove" (followed by a separate signal with "post_remove" ) |
reverse |
True (Pizza contains the ManyToManyField , so this call modifies the reverse relation) |
model |
Pizza (the class of the objects removed from the Topping ) |
pk_set |
{p.id} (since only Pizza p was removed from the relation) |
using |
"default" (since the default router sends writes here) |
class_prepared
-
django.db.models.signals.class_prepared
Sent whenever a model class has been “prepared” – that is, once model has been defined and registered with Django’s model system. Django uses this signal internally; it’s not generally used in third-party applications.
Since this signal is sent during the app registry population process, and AppConfig.ready()
runs after the app registry is fully populated, receivers cannot be connected in that method. One possibility is to connect them AppConfig.__init__()
instead, taking care not to import models or trigger calls to the app registry.
Arguments that are sent with this signal:
-
sender
- The model class which was just prepared.
Management signals
Signals sent by django-admin.
pre_migrate
-
django.db.models.signals.pre_migrate
Sent by the migrate
command before it starts to install an application. It’s not emitted for applications that lack a models
module.
Arguments sent with this signal:
-
sender
- An
AppConfig
instance for the application about to be migrated/synced. -
app_config
- Same as
sender
. -
verbosity
-
Indicates how much information manage.py is printing on screen. See the
--verbosity
flag for details.Functions which listen for
pre_migrate
should adjust what they output to the screen based on the value of this argument. -
interactive
-
If
interactive
isTrue
, it’s safe to prompt the user to input things on the command line. Ifinteractive
isFalse
, functions which listen for this signal should not try to prompt for anything.For example, the
django.contrib.auth
app only prompts to create a superuser wheninteractive
isTrue
. -
using
- The alias of database on which a command will operate.
post_migrate
-
django.db.models.signals.post_migrate
Sent by the migrate
command after it installs an application, and the flush
command. It’s not emitted for applications that lack a models
module.
It is important that handlers of this signal perform idempotent changes (e.g. no database alterations) as this may cause the flush
management command to fail if it also ran during the migrate
command.
Arguments sent with this signal:
-
sender
- An
AppConfig
instance for the application that was just installed. -
app_config
- Same as
sender
. -
verbosity
-
Indicates how much information manage.py is printing on screen. See the
--verbosity
flag for details.Functions which listen for
post_migrate
should adjust what they output to the screen based on the value of this argument. -
interactive
-
If
interactive
isTrue
, it’s safe to prompt the user to input things on the command line. Ifinteractive
isFalse
, functions which listen for this signal should not try to prompt for anything.For example, the
django.contrib.auth
app only prompts to create a superuser wheninteractive
isTrue
. -
using
- The database alias used for synchronization. Defaults to the
default
database.
For example, you could register a callback in an AppConfig
like this:
from django.apps import AppConfig from django.db.models.signals import post_migrate def my_callback(sender, **kwargs): # Your specific logic here pass class MyAppConfig(AppConfig): ... def ready(self): post_migrate.connect(my_callback, sender=self)
Note
If you provide an AppConfig
instance as the sender argument, please ensure that the signal is registered in ready()
. AppConfig
s are recreated for tests that run with a modified set of INSTALLED_APPS
(such as when settings are overridden) and such signals should be connected for each new AppConfig
instance.
Request/response signals
Signals sent by the core framework when processing a request.
request_started
-
django.core.signals.request_started
Sent when Django begins processing an HTTP request.
Arguments sent with this signal:
-
sender
- The handler class – e.g.
django.core.handlers.wsgi.WsgiHandler
– that handled the request. -
environ
- The
environ
dictionary provided to the request.
The environ
argument was added.
request_finished
-
django.core.signals.request_finished
Sent when Django finishes delivering an HTTP response to the client.
Note
Some WSGI servers and middleware do not always call close
on the response object after handling a request, most notably uWSGI prior to 1.2.6 and Sentry’s error reporting middleware up to 2.0.7. In those cases this signal isn’t sent at all. This can result in idle connections to database and memcache servers.
Arguments sent with this signal:
-
sender
- The handler class, as above.
got_request_exception
-
django.core.signals.got_request_exception
This signal is sent whenever Django encounters an exception while processing an incoming HTTP request.
Arguments sent with this signal:
-
sender
- The handler class, as above.
-
request
- The
HttpRequest
object.
Test signals
Signals only sent when running tests.
setting_changed
-
django.test.signals.setting_changed
This signal is sent when the value of a setting is changed through the django.test.TestCase.settings()
context manager or the django.test.override_settings()
decorator/context manager.
It’s actually sent twice: when the new value is applied (“setup”) and when the original value is restored (“teardown”). Use the enter
argument to distinguish between the two.
You can also import this signal from django.core.signals
to avoid importing from django.test
in non-test situations.
The signal was moved to django.core.signals
as described above.
Arguments sent with this signal:
-
sender
- The settings handler.
-
setting
- The name of the setting.
-
value
- The value of the setting after the change. For settings that initially don’t exist, in the “teardown” phase,
value
isNone
. -
enter
- A boolean;
True
if the setting is applied,False
if restored.
template_rendered
-
django.test.signals.template_rendered
Sent when the test system renders a template. This signal is not emitted during normal operation of a Django server – it is only available during testing.
Arguments sent with this signal:
-
sender
- The
Template
object which was rendered. -
template
- Same as sender
-
context
- The
Context
with which the template was rendered.
Database Wrappers
Signals sent by the database wrapper when a database connection is initiated.
connection_created
-
django.db.backends.signals.connection_created
Sent when the database wrapper makes the initial connection to the database. This is particularly useful if you’d like to send any post connection commands to the SQL backend.
Arguments sent with this signal:
-
sender
- The database wrapper class – i.e.
django.db.backends.postgresql.DatabaseWrapper
ordjango.db.backends.mysql.DatabaseWrapper
, etc. -
connection
- The database connection that was opened. This can be used in a multiple-database configuration to differentiate connection signals from different databases.
© Django Software Foundation and individual contributors
Licensed under the BSD License.
https://docs.djangoproject.com/en/1.9/ref/signals/