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 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=<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 the post_init signal, so _state attributes always have their default values. For example, _state.db is None and cannot be used to check an instance database.

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(), or None if update_fields wasn’t passed to save().

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(), or None if update_fields wasn’t passed to save().

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: