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 the save() 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 the save() 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 the through 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 the ManyToManyField 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 and post_remove actions, this is a set of primary key values that have been added to or removed from the relation.
For the pre_clear and post_clear actions, this is None.
- 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.objects.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 | 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 | 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.
pre_syncdb¶
- django.db.models.signals.pre_syncdb¶
Sent by the syncdb command before it starts to install an application.
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.
Arguments sent with this signal:
- sender
- The models module that was just installed. That is, if syncdb just installed an app called "foo.bar.myapp", sender will be the foo.bar.myapp.models module.
- app
- Same as sender.
- create_models
- A list of the model classes from any app which syncdb plans to create.
- verbosity
Indicates how much information manage.py is printing on screen. See the --verbosity flag for details.
Functions which listen for pre_syncdb should adjust what they output to the screen based on the value of this argument.
- interactive
If interactive is True, it’s safe to prompt the user to input things on the command line. If interactive is False, 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 when interactive is True.
- db
- The alias of database on which a command will operate.
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, if syncdb just installed an app called "foo.bar.myapp", sender will be the foo.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 is True, it’s safe to prompt the user to input things on the command line. If interactive is False, 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 when interactive is True.
- db
- The database alias used for synchronization. Defaults to the default database.
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.
Before Django 1.5, this signal was sent before delivering content to the client. In order to accommodate streaming responses, it is now sent after the response has been fully delivered 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.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”). Use the enter argument to distinguish between the two.
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 is None.
- enter
- New in Django Development version:
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_psycopg2.DatabaseWrapper or django.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.
Questions/Feedback
Having trouble? We'd like to help!
- Try the FAQ — it's got answers to many common questions.
- Search for information in the archives of the django-users mailing list, or post a question.
- Ask a question in the #django IRC channel, or search the IRC logs to see if it has been asked before.
- If you notice errors with this documentation, please open a ticket and let us know! Please only use the ticket tracker for criticisms and improvements on the docs. For tech support, use the resources above.