models.py

from django.db import models


class Bar(models.Model):
    spam = models.EmailField()


class Foo(models.Model):
    bars = models.ManyToManyField(Bar, through='ThroughFooBars')


class ThroughFooBars(models.Model):
    foo = models.ForeignKey(Foo, models.DO_NOTHING)
    bar = models.ForeignKey(Bar, models.DO_NOTHING)
    order = models.PositiveIntegerField(default=0)

    class Meta:
        db_table = 'through_foo_bars'
        unique_together = (('foo', 'bar'),)
        ordering = ('order',)