Django 1.6 如何同时正确注释 Count() 和 Sum()？

Question

简单描述:

#for each q in Question , q.votes is correct
Question.objects.annotate(votes=Sum('vote__value')) 
#add a Count annotate, q.answers is correct, while q.votes not.
Question.objects.annotate(votes=Sum('vote__value', distinct=True),answers=Count('answer', distinct=True),)

如果我想同时注释Count()和Sum()，怎么办？因此我可以做类似的事情:

qs = Question.objects.annotate(votes=Sum('vote__value', distinct=True),answers=Count('answer', distinct=True),)
for q in qs:
    #do something with q.votes and q.answers in a template
    #this will be convenient.

Click Here如果需要，可以下载测试项目代码。测试函数在raw.tests.test()中

Answer 1

使用 Django 1.11，您可以使用 Subquery()

votes = Vote.objects.filter(question=OuterRef('pk').order_by().values('question')
sum_votes = votes.annotate(s=Sum('value')).values('s')

answers = Answer.objects.filter(question=OuterRef('pk').order_by().values('question')
count_answers = answers.annotate(c=Count('*')).values('c')

qs = Question.objects.annotate(votes=Subquery(sum_votes),
                               answers=Subquery(count_answers))