Sending and receiving signals in django models

Question

I am using django 2.0.8 and Python 3.5. I want to be able to send and receive custom signals when an object is saved to the database.

I have followed the Django documentation on listening to signals and also the core signals bundled with Django - however, I am unable to get my example to work.

This is what I have so far:

myapp/models.py

from django.db import models
import django.dispatch

my_signal = django.dispatch.Signal(providing_args=["name"])

class Foo(models.Model):
    name = models.CharField(max_length=16)

def save(self, *args, **kwargs):
    try:
        # Call the "real" save() method.
        super().save(*args, **kwargs)  

        # Fire off signal         
        my_signal.send(sender=self.__class__, name=self.name)

    except Exception as e:
        print ('Exception:', e)
        #pass

myapp/signals.py

from django.db.models.signals import post_save
from django.dispatch import receiver
from .models import Foo


@receiver(post_save, sender=Foo)
def foo_handler(sender, **kwargs):
    print('Foo Signal Recieved!')
    print(kwargs)

myapp/app.py

class MyappConfig(AppConfig):
    name = 'myapp'
    label = 'myapp'

    def ready(self):
        import myapp.signals

Sample usage

from myapp.models import Foo

foo = Foo(name='Homer Simpson')
foo.save() # Object is saved, but event is not fired!

Can anyone explain why the signal is not being fired?

Answer 1

It seems you need two features supplied by Django. signal and contenttypes.

So read the doc first

The model Activity is related to contenttypes,seems you miss object_id Field, which indicate which model instance is being crud.

For every crud action, An Activity instance is being created.This part is just the code written in signal.py

signal: signal have to connect each concrete model. Fortunately,See the source code of decorator receiver.

We have a signal list [post_save,post_delete] and a model list (FoodooChile, FooBarChile) to connect .

In post_save,argument created indicate the action is create or update.

At last, Usually we import the signal file in urls.py, maybe not the best practice.

---

It is also related to your settings.py. use 'myapp.apps.MyappConfig' replace myapp in settings.py,or define default_app_config = 'myapp.apps.MyappConfig' in myapp/__init__.py. The link above in comments describe this in detail