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我遇到了一个问题，在保存之前我无法检索到实例的值。它返回save()方法中的更新值。此外，我无法存储在__init__中，因为它运行的查询太多。我要运行的查询，只有当用户保存该实例在保存之前在Django模型中检索属性
这里是我的模型简化：
class Users(models.Model):
username = models.CharField(max_length=20)
class Groups(models.Model):
name = models.CharField(max_length=100)
user = models.ManyToManyField(Users)
'''def __init__(self, *args, **kwargs):
super(Groups, self).__init__(*args, **kwargs)
#store original values
for field in Groups._meta.get_fields():
f = field
if not f.many_to_many:
setattr(self, '__original_%s' % f.name, getattr(self, f.name))
else:
userlist = Users.objects.all().filter(groups__id=self.pk)
setattr(self, '__original_userlist', set(userlist)) #set() to force lazy query and get original value'''
#function trying to reproduce __init__
def store(self):
for field in Groups._meta.get_fields():
f = field
if not f.many_to_many:
setattr(self, '__original_%s' % f.name, getattr(self, f.name))
else:
userlist = Users.objects.all().filter(groups__id=self.pk)
setattr(self, '__original_userlist', set(userlist)) #set() to force lazy query
def save(self, *args, **kwargs):
self.store()
print(getattr(self, '__original_userlist')) #return the list with users
super(Groups, self).save(*args, **kwargs)
print(getattr(self, '__original_userlist')) #return the list with users
我不知道最好的办法的办法，因为我必须作出查询。我这样做来比较旧的和新的值，然后我可以在日志文件中存储不同的值。