Signals¶

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:

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 list 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.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:

And if we would then do something like this:

>>> t.pizza_set.remove(p)

the arguments sent to a m2m_changed handler would be:

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.

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.

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_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.

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.

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 is None.

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.

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.