如何在django中处理未保存的多对多关系？

from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=100)

class Group(models.Model):
    name = models.CharField(max_length=100)
    members = models.ManyToManyField(Person, through='Membership')

class Membership(models.Model):
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=100)

# 创建一个新的 Person 和 Group 对象
person = Person.objects.create(name='John')
group = Group.objects.create(name='Friends')

# 创建一个新的 Membership 对象，将 Person 和 Group 对象关联起来
membership = Membership(person=person, group=group, date_joined=datetime.date.today(), invite_reason='Neighbors')
membership.save()

# 获取 Person 对象的所有关联的 Group 对象
groups = person.group_set.all()

# 获取 Group 对象的所有关联的 Person 对象
people = group.person_set.all()

# 更新 Membership 对象中的 invite_reason 字段
membership.invite_reason = 'New reason'
membership.save()

# 删除 Membership 对象，同时删除 Person 和 Group 之间的关系
membership.delete()