from django.contrib.auth.models import User, Group

from django.db import models

class Owner(models.Model):

    user = models.ForeignKey(User, blank=True, null=True)

    group = models.ForeignKey(Group, blank=True, null=True)

    def __unicode__(self):

        if self.user:

            return self.user.username

        else:

            return self.group.name

class Document(models.Model):

    owner = models.ForeignKey(Owner, blank=True, null=True)

    class Meta:

        abstract = True