Signals¶
A list of all the signals that Django sends.
See also
See the documentation on the signal dispatcher for information regarding how to register for and receive signals.
The comment framework sends a set of comment-related 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
module 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()
.
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 explicitly specified in the
save()
method.None
if this argument was not used in thesave()
call.
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 explicitly specified in the
save()
method.None
if this argument was not used in thesave()
call.
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 list 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:
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.object.create(...)
>>> t = Topping.objects.create(...)
>>> p.toppings.add(t)
the arguments sent to a m2m_changed
handler (topppings_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.
Arguments that are sent with this signal:
sender
- The model class which was just prepared.
Management signals¶
Signals sent by django-admin.
post_syncdb¶
-
django.db.models.signals.
post_syncdb
¶
Sent by the syncdb
command after it installs an application, and the
flush
command.
Any handlers that listen to this signal need to be written in a particular
place: a management
module in one of your INSTALLED_APPS
. If
handlers are registered anywhere else they may not be loaded by
syncdb
. 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
syncdb
command.
Arguments sent with this signal:
sender
- The
models
module that was just installed. That is, ifsyncdb
just installed an app called"foo.bar.myapp"
,sender
will be thefoo.bar.myapp.models
module. app
- Same as
sender
. created_models
- A list of the model classes from any app which
syncdb
has created so far. verbosity
Indicates how much information manage.py is printing on screen. See the
--verbosity
flag for details.Functions which listen for
post_syncdb
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
.
For example, yourapp/management/__init__.py
could be written like:
from django.db.models.signals import post_syncdb
import yourapp.models
def my_callback(sender, **kwargs):
# Your specific logic here
pass
post_syncdb.connect(my_callback, sender=yourapp.models)
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.
request_finished¶
-
django.core.signals.
request_finished
¶
Sent when Django finishes processing an HTTP request.
Note
When a view returns a streaming response, this signal is sent only after the entire response is consumed by the client (strictly speaking, by the WSGI gateway).
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.utils.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”).
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
.
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_psycopg2.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.