Another model for a notification

models.py

class Notification(models.Model):
    sender = models.ForeignKey('auth.User', null=True)
    recipient = models.ForeignKey('auth.User', related_name='notifications')

    subject = models.CharField(max_length=255)
    body = models.TextField()

    # Some projects may want to categorise their notifications.  You may want
    # to use this field to show a different icons next to the notification.
    category = models.CharField(max_length=255, null=True)

    INBOX, ARCHIVE = 'Inbox', 'Archive'
    choices = (
        (INBOX, _(INBOX)),
        (ARCHIVE, _(ARCHIVE)))
    location = models.CharField(max_length=32, choices=choices,
                                default=INBOX)

    date_sent = models.DateTimeField(auto_now_add=True)
    date_read = models.DateTimeField(null=True)