Django has long supported "signals", a feature that can be really useful. It allows you to get notified in a callback when a certain event occurs. One of the most common use cases is connecting to model signals. These signals get triggered when a model gets saved, or deleted.

Django's built-in signals have one major flaw:

• The QuerySet.update(..) method does not emit any signals.

Because of this limitation, Django's signals cannot be reliably used to be signaled on model changes. django-postges-extra adds three new signals which are much more primitive, but work reliably across the board.

The signals defined by this library are completely valid, standard Django signals. Therefore, their documentation also applies: https://docs.djangoproject.com/en/1.10/topics/signals/.

Each of the signals send upon model modification send one parameter containing the value of the primary key of the row that was affected. Therefore the signal's signature looks like this:

def my_receiver(sender, pk: int):
    # pk is the primary key, a keyword argument

psqlextra.signals.create

Send after a new model instance was created.

from django.db import models
from psqlextra.models import PostgresModel
from psqlextra import signals

class MyModel(PostgresModel):
    myfield = models.CharField(max_length=255, unique=True)

def on_create(sender, **kwargs):
     print('model created with pk %d' % kwargs['pk'])

signals.create.connect(MyModel, on_create, weak=False)

# this will trigger the signal
instance = MyModel(myfield='cookies')
instance.save()

# but so will this
MyModel.objects.create(myfield='cheers')

psqlextra.signals.update

Send after a new model instance was updated.

from django.db import models
from psqlextra.models import PostgresModel
from psqlextra import signals

class MyModel(PostgresModel):
    myfield = models.CharField(max_length=255, unique=True)

def on_update(sender, **kwargs):
     print('model updated with pk %d' % kwargs['pk'])

signals.update.connect(MyModel, on_update, weak=False)

# for every row that is affected, the signal will be send
MyModel.objects.filter(myfield='cookies').update(myfield='cheers')

psqlextra.signals.delete

Send before a new model instance is deleted.

from django.db import models
from psqlextra.models import PostgresModel
from psqlextra import signals

class MyModel(PostgresModel):
    myfield = models.CharField(max_length=255, unique=True)

def on_delete(sender, **kwargs):
     print('model deleted with pk %d' % kwargs['pk'])

signals.delete.connect(MyModel, on_update, weak=False)

# for every row that is affected, the signal will be send
MyModel.objects.filter(myfield='cookies').delete()

# in this case, a single row is deleted, the signal will be send
# for this particular row
MyModel.objects.get(id=1).delete()