Making Django's Signals Async with Celery

#django #python

Prepare

Django project with long-task logic
Celery with any backend

For example: send push after any event or auth user through sms code or email link.

Mark: to sign-in/sign-up users via SMS you may use this library

Problems

Django signals synchronous by default
We must to wait when transaction completed
Clients can to wait response for a long time

Short description

Configure celery
Create application (for example, notifier)
Configure post_save signal through celery task
Configure AppConfig to load function

Detail

Create notifier application
Add tasks.py

tasks.py

import uuid
from collections import namedtuple
from django.db.models.signals import post_save
from run_celery import app

from some_apps.models import SomeModel1, SomeModel2, SomeModel3

Ctx = namedtuple('Ctx', 'class_name identifier')

models = [
  SomeModel1, 
  SomeModel2, 
  SomeModel3
]


def register_models():
    for model in models:
        post_save.connect(_post_save,
                          sender=model,
                          dispatch_uid=uuid.uuid4())


def _post_save(sender, instance, **kwargs):
    ctx = Ctx(class_name=instance.__class__.__name__,
                        identifier=instance.pk)
    _async_post_save_handler.delay(ctx)


@app.task
def _async_post_save_handler(ctx: Ctx):
    """
    Get model and instance from notifier object and then make
    some other logic
    """
  ...

Finally, add to apps.py:


from django.apps import AppConfig


class NotifierConfig(AppConfig):
    name = 'notifier'

    def ready(self):
        from apps.notifier.tasks import register_models
        register_models() # here!