聚合函数返回AttributeError:'Sum'对象没有属性'lookup'

Question

我正在尝试聚合函数,我得到了这个奇怪的结果(最新的官方Django 1.2版本).这是模型:

class Reputation(models.Model):
    user = models.ForeignKey(User)
    modifier = models.IntegerField()
    activity = models.ForeignKey(Activity)

这就是我得到的:

In [37]: Reputation.objects.aggregate(r=Sum('modifier'))
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)

C:\Data\Development\django_projects\oko\lib\site-packages\django\db\models\manager.pyc in aggregate(self, *args, **kwargs)
    142
    143     def aggregate(self, *args, **kwargs):
--> 144         return self.get_query_set().aggregate(*args, **kwargs)
    145
    146     def annotate(self, *args, **kwargs):

C:\Data\Development\django_projects\oko\lib\site-packages\django\db\models\query.pyc in aggregate(self, *args, **kwargs)
    315         for (alias, aggregate_expr) in kwargs.items():
    316             query.add_aggregate(aggregate_expr, self.model, alias,
--> 317                 is_summary=True)
    318
    319         return query.get_aggregation(using=self.db)

C:\Data\Development\django_projects\oko\lib\site-packages\django\db\models\sql\query.pyc in add_aggregate(self, aggregate, model, alias, is_summary)
    929         """
    930         opts = model._meta
--> 931         field_list = aggregate.lookup.split(LOOKUP_SEP)
    932         if len(field_list) == 1 and aggregate.lookup in self.aggregates:
    933             # Aggregate is over an annotation

AttributeError: 'Sum' object has no attribute 'lookup'

Answer 1

确保导入正确的Sum:

from django.db.models import Sum

如果导入django.db.models.sql.aggregates.Sum,您将继续看到该错误.