Examples

Emails

Sending an email can take a while so why not queue it:

# Welcome mail with follow up example
from datetime import timedelta
from django.utils import timezone
from django_q import async, schedule, Schedule


def welcome_mail(user):
    msg = 'Welcome to our website'
    # send this message right away
    async('django.core.mail.send_mail',
          'Welcome',
          msg,
          'from@example.com',
          [user.email])
    # and this follow up email in one hour
    msg = 'Here are some tips to get you started...'
    schedule('django.core.mail.send_mail',
             'Follow up',
             msg,
             'from@example.com',
             [user.email],
             schedule_type=Schedule.ONCE,
             next_run=timezone.now() + timedelta(hours=1))

    # since the `repeats` defaults to -1
    # this schedule will erase itself after having run

Since you’re only telling Django Q to take care of the emails, you can quickly move on to serving web pages to your user.

Signals

A good place to use async tasks are Django’s model signals. You don’t want to delay the saving or creation of objects, but sometimes you want to trigger a lot of actions:

# Message on object change
from django.contrib.auth.models import User
from django.db.models.signals import pre_save
from django.dispatch import receiver
from django_q import async

# set up the pre_save signal for our user
@receiver(pre_save, sender=User)
def email_changed(sender, instance, **kwargs):
    try:
        user = sender.objects.get(pk=instance.pk)
    except sender.DoesNotExist:
        pass  # new user
    else:
        # has his email changed?
        if not user.email == instance.email:
            # tell everyone
            async('tasks.inform_everyone', instance)

The task will send a message to everyone else informing them that the users email address has changed. Note that this adds almost no overhead to the save action:

# tasks.py
def inform_everyone(user):
    mails = []
    for u in User.objects.exclude(pk=user.pk):
        msg = 'Dear {}, {} has a new email address: {}'
        msg = msg.format(u.username, user.username, user.email)
        mails.append(('New email', msg,
                      'from@example.com', [u.email]))
    return send_mass_mail(mails)

# or do it async again
def inform_everyone_async(user):
    for u in User.objects.exclude(pk=user.pk):
        msg = 'Dear {}, {} has a new email address: {}'
        msg = msg.format(u.username, user.username, user.email)
        async('django.core.mail.send_mail',
              'New email', msg, 'from@example.com', [u.email])

Of course you can do other things beside sending emails. These are just generic examples. You can use signals with async to update fields in other objects too. Let’s say this users email address is not just on the User object, but you stored it in some other places too without a reference. By attaching an async action to the save signal, you can now update that email address in those other places without impacting the the time it takes to return your views.

Reports

In this example the user requests a report and we let the cluster do the generating, while handling the result with a hook.

# Report generation with hook example
from django_q import async

# views.py
# user requests a report.
def create_report(request):
    async('tasks.create_html_report',
          request.user,
          hook='tasks.email_report')

# tasks.py
# report generator
def create_html_report(user):
    html_report = 'We had a great quarter!'
    return html_report

# report mailer
def email_report(task):
    if task.success:
        # Email the report
        async('django.core.mail.send_mail',
              'The report you requested',
              task.result,
              'from@example.com',
              task.args[0].email)
    else:
        # Tell the admins something went wrong
        async('django.core.mail.mail_admins',
              'Report generation failed',
              task.result)

The hook is practical here, cause it allows us to detach the sending task from the report generation function and to report on possible failures.

Note

If you have an example you want to share, please submit a pull request on github.