Periodically fetch data and display it with Django

Question

I would like to implement a kind of "real-time" notification system in my Django application.

I would store some messages destined to a specific user in my database. When a user is logged in the application, if there is a notification for him in the database, then the application displays it using the messages framework. When he clicks on the message, it is deleted from the database.

I am a bit stuck on the "fetch the data every minute" thing. I heard of celery (http://docs.celeryproject.org/en/latest/#), but I would like to be sure it is the way to go there before diving in, because it seems a bit complicated to set up and use.

If there is an easy way to daemonise a django fonction, or if something similar to what I want to do already exist, I would appreciate any hint !

Answer 1

If is just a simple task, you may do with Ajax.

Just declare one URL for the ajax query:

#urls.py

...
url(r'^ajax/my_query$', my_app.views.ajax_processor)
...

then in your my_app/views.py:

#views.py

def ajax_processor(request):

    ... do the processing you want as if it is a normal web request.
    ... like querying the database
    ... you can return a `json` dictionary 
    ... or a normal `render_to_response` template with html

That should do on the server side. On the client side it would be lovely to use jQuery with the $.ajax function and do this:

$.ajax({
    url:'/ajax/my_query',  // a normal get request
    success:function(data){  // success is the callback when the server responds
        /* if is json what you decided to return then process the json dict
           if is normal html render it wherver you want
        */
    }
});

Is just a simple set up, a bit of code in server-side and a bit of code in client-side.

If you are planning to develop a heavily real-time based application then you should rely on a better library, but if you only need to do a little query asynchronous then you may consider this way.

Here is a good and simple ajax tutorial provided by the W3Schools to help you understand Ajax, and here you can find useful information about polling with ajax/jquery.

Good luck!

Answer 2

Here are some options to consider:

• celery. Yes, it's not that trivial to set up, but it's very easy to configure and use from your python/django side via django-celery. Also take a look at celery periodic tasks.

• rq (Redis Queue). Simple job queue that is easy to set up.

• django-cronograph. Creating and running cron jobs easily from admin commands.

Also see:

• Examples of Django and Celery: Periodic Tasks
• Django - Set Up A Scheduled Job?