A data migration for every Django project

How to use a South data migration to avoid accidentally sending emails from example.com.

Problem

Consider the following snippet from Django’s docs¹ for sending a confirmation email:

from django.contrib.sites.models import Site
from django.core.mail import send_mail

def register_for_newsletter(request):
    current_site = Site.objects.get_current()
    send_mail(
        'Thanks for subscribing to %s alerts' % current_site.name,
        'Thanks for your subscription. We appreciate it.\n\n-The %s team.' % current_site.name,
        'editor@%s' % current_site.domain,
        [user.email]
    )

Here the domain for the email sender is taken from the ‘current site’ instance, which is controlled by Django’s ‘Sites’ framework and accessible by a custom method on the manager of the Site model.

By default, a Site instance is created with domain and display name ’example.com’ and you have to correct these values. This is often done by hand using the admin suite.

However, as with any manual change, it’s easy to forget and you’ll often find Django projects sending email from editor@example.com. Highly embarrassing.

Solution

Automation, of course! We can use a South data migration to set the domain and display name correctly in each environment.

First, ensure that each environment has settings for the domain and site name.

# conf/test.py
...
DOMAIN_NAME = 'test.project.client.tangentlabs.co.uk'
SITE_NAME = 'project - client (test)'

# conf/stage.py
...
DOMAIN_NAME = 'stage.project.client.tangentlabs.co.uk'
SITE_NAME = 'project - client (stage)'

This snippet assumes you are using a set-up similar to that outlined by David Cramer, where an environmental variable specifies an additional settings file to import. You don’t have to use this method; employing a settings_local.py file for each environment works just as well.

Next, create a data migration to set the domain and display name correctly in each environment. This migration sits most naturally in the django.contrib.sites app, but since that’s in Django’s core, it’s not an option. You could use an existing app within your project to house the migration or perhaps create a simple ‘core’ or ‘data’ app to house data migrations that alter 3rd party apps.

Since we’re not using the actual app where the Site model is defined, we must employ South’s --freeze option to ensure the Site model is available to the migration.

python manage.py datamigration <appname> create_domains --freeze=sites

Finally implement the forwards method:

from south.v2 import DataMigration
from django.conf import settings

class Migration(DataMigration):

    def forwards(self, orm):
        Site = orm['sites.Site']
        site = Site.objects.get(id=settings.SITE_ID)
        site.domain = settings.DOMAIN_NAME
        site.name = settings.SITE_NAME
        site.save()

Then your next deployment to each environment will perform the update.