def __unicode__(self):
    return self.name


class Group(models.Model):
    name = models.CharField(max_length=128)
members = models.ManyToManyField(Person, through='Membership')

def __unicode__(self):
    return self.name


class Membership(models.Model):
    person = models.ForeignKey(Person)
group = models.ForeignKey(Group)
date_joined = models.DateField()
invite_reason = models.CharField(max_length=64)
Как добавить столбец в таблицу ManyToMany (Django)