考虑以下模型:
class User(AbstractUser):
def messages(self):
return Message.objects.filter(user=self).order_by('-created_on')
class Message(models.Model):
user = models.ForeignKey('account.User', related_name='message', on_delete=models.CASCADE)
created_on = models.DateTimeField(auto_now=True)
data = models.TextField()
read = models.BooleanField(default=False)
objects = MessageManager()
我想重写 Message
模型的 QuerySet 行为以包含自定义方法 unread_count
:
class MessageManager(models.Manager):
def get_queryset(self):
queryset = super().get_queryset()
unread_count = queryset.filter(read=False).count()
print(unread_count) # this works
# these don't work
queryset.unread_count = unread_count
setattr(queryset, 'unread_count', unread_count)
#
return queryset
messages
方法工作正常,并且管理器内的 print 语句执行,但如果我尝试访问 unread_count
,我会收到 AttributeError
:
>>>user = User.objects.get(id=1)
>>>messages = user.messages()
2 # this is from the print statement
>>>messages.unread_count
AttributeError: 'QuerySet' object has no attribute 'unread_count'
我在这里缺少什么?
最佳答案
您应该对 models.QuerySet
进行子类化,而不是 models.Manager
:
class MessageQuerySet(models.QuerySet):
@property
def unread_count(self):
return self.filter(read=False).count()
然后使用as_manager
模型中的方法:
class Message(models.Model):
...
objects = MessageQuerySet.as_manager()
如果您需要向从管理器返回的 QuerySet
以及管理器本身添加方法,则需要使用 from_queryset
:
class MessageManager(models.Manager):
def some_manager_only_method(self):
print('do stuff')
class MessageQuerySet(models.QuerySet):
@property
def unread_count(self):
return self.filter(read=False).count()
class Message(models.Model):
...
objects = MessageManager.from_queryset(MessageQuerySet)()
关于python - 如何在 Django 中向查询集添加自定义属性?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58210689/