万一链接中断：
from django.db import modelsclass Person(models.Model): name = models.CharField(max_length=128) def __str__(self): # __unipre__ on Python 2 return self.nameclass Group(models.Model): name = models.CharField(max_length=128) members = models.ManyToManyField(Person, through='Membership') def __str__(self): # __unipre__ on Python 2 return self.nameclass Membership(models.Model): person = models.ForeignKey(Person) group = models.ForeignKey(Group) date_joined = models.DateField() invite_reason = models.CharField(max_length=64)
