class Person(models.Model):
    name = models.CharField(max_length=128)

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
How to add column in ManyToMany Table (Django)