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
Signals can make your code harder to maintain. Consider implementing a helper method on a custom manager, to both update your models and perform additional logic, or else overriding model methods before using model signals.
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 these 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
Question
model defined in the polls
application could be referenced
as 'polls.Question'
. 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:
q = Question(question_text="What's new?", pub_date=timezone.now())
The arguments sent to a pre_init
handler would be:
Argument | Value |
---|---|
sender |
Question (the class itself) |
args |
[] (an empty list because there were no positional
arguments passed to __init__() ) |
kwargs |
{'question_text': "What's new?",
'pub_date': datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=datetime.timezone.utc)} |
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.
Note
instance._state
isn’t set before sending thepost_init
signal, so_state
attributes always have their default values. For example,_state.db
isNone
.
Warning
For performance reasons, you shouldn’t perform queries in receivers of
pre_init
or post_init
signals because they would be executed for
each instance returned during queryset iteration.
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.
origin
- New in Django Development version.
The origin of the deletion being the instance of a
Model
orQuerySet
class.
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.
origin
- New in Django Development version.
The origin of the deletion being the instance of a
Model
orQuerySet
class.
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
andpost_add
actions, this is a set of primary key values that will be, or have been, added to the relation. This may be a subset of the values submitted to be added, since inserts must filter existing values in order to avoid a databaseIntegrityError
.For the
pre_remove
andpost_remove
actions, this is a set of primary key values that was submitted to be removed from the relation. This is not dependent on whether the values actually will be, or have been, removed. In particular, non-existent values may be submitted, and will appear inpk_set
, even though they have no effect on the database.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 a 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
.stdout
- A stream-like object where verbose output should be redirected.
using
- The alias of database on which a command will operate.
plan
- The migration plan that is going to be used for the migration run. While
the plan is not public API, this allows for the rare cases when it is
necessary to know the plan. A plan is a list of two-tuples with the first
item being the instance of a migration class and the second item showing
if the migration was rolled back (
True
) or applied (False
). apps
- An instance of
Apps
containing the state of the project before the migration run. It should be used instead of the globalapps
registry to retrieve the models you want to perform operations on.
post_migrate
¶
-
django.db.models.signals.
post_migrate
¶
Sent at the end of the migrate
(even if no migrations are run) and
flush
commands. It’s not emitted for applications that lack a
models
module.
Handlers of this signal must not perform database schema alterations as doing
so may cause the flush
command to fail if it runs 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
.stdout
- A stream-like object where verbose output should be redirected.
using
- The database alias used for synchronization. Defaults to the
default
database. plan
- The migration plan that was used for the migration run. While the plan is
not public API, this allows for the rare cases when it is necessary to
know the plan. A plan is a list of two-tuples with the first item being
the instance of a migration class and the second item showing if the
migration was rolled back (
True
) or applied (False
). apps
- An instance of
Apps
containing the state of the project after the migration run. It should be used instead of the globalapps
registry to retrieve the models you want to perform operations on.
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.
Warning
Signals can make your code harder to maintain. Consider using a middleware before using request/response signals.
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.
request_finished
¶
-
django.core.signals.
request_finished
¶
Sent when Django finishes delivering an HTTP response to the client.
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
- Unused (always
None
). 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.
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.
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.