def clear_expiration_field_for_expired_jobs(self):
        '''Set the expiration date of every job that has expired.'''
        # Only select rows where there is an expiration date set
        for job in JobPriority.objects.filter(expiration_date__isnull=False):
            if job.has_expired():
                job.expiration_date = None
                job.save()
Set the expiration date of every job that has expired.