Question

我是django框架和Python的新手。我要求对用户在运行时选择的字段进行聚合

class Department(models.Model):
  code = models.CharField(max_length=10, primary_key=True)
  size = models.IntegerField(blank=True, null=True)
  budget = models.IntegerField(blank=True, null=True)

我想通过执行类似以下的操作，选择使用** kwarg执行大小，预算或两者的总和

from django.db.models import Avg, Count, Sum
# let Fname has the name of the field to sum on, set by a user input
FName='size' 
FList={}
# problem in passing the following
FList['total_size']="Sum(' "+FName+" ')" 
data=Department.objects.annotate(**FList)

但我收到以下错误

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "c:\python34\lib\site-packages\django\db\models\query.py", line 802, in annotate
    is_summary=False)
  File "c:\python34\lib\site-packages\django\db\models\sql\query.py", line 1030, in add_aggregate
    field_list = aggregate.lookup.split(LOOKUP_SEP)
AttributeError: 'str' object has no attribute 'lookup'

从列表中的讨论中暗示，在密钥，值对

中无法识别Sum

赞赏将** kwarg传递给注释的任何帮助

Answer 1

你传递字符串“Sum（blah）”，因此错误。

FList['total_size'] = Sum(FName)

但实际上没有理由在这里使用kwargs：

data=Department.objects.annotate(total_size=Sum(FName))

Answer 2

简化..

from django.db.models import Avg, Count, Sum
# let Fname has the name of the field to sum on, set by a user input
FName='size' 
data=Department.objects.annotate(total_size=Sum(FName))

由于FName是一个字符串，因此您不需要用引号将其包装起来。如果你需要运行一个不同的功能，比如avg等...

from django.db.models import Avg, Count, Sum
# let Fname has the name of the field to sum on, set by a user input
FName='size' 
function_t = Sum # or Avg, or Count
data=Department.objects.annotate(total_size=function_t(FName))

我希望这可以帮助你走上正轨

Django：如何将** kwarg传递给annotate（）

2 个答案: