如何做嵌套组由与注释在django orm?

Question

我有以下数据:

publisher                    title
--------------------------  -----------------------------------
New Age Books                Life Without Fear
New Age Books                Life Without Fear
New Age Books                Sushi, Anyone?
Binnet & Hardley             Life Without Fear
Binnet & Hardley             The Gourmet Microwave
Binnet & Hardley             Silicon Valley
Algodata Infosystems         But Is It User Friendly?
Algodata Infosystems         But Is It User Friendly?
Algodata Infosystems         But Is It User Friendly?

我想做的是:我想计算每个作者出版了多少本同名的书。我想得到以下结果:

{publisher: New Age Books, title: Life Without Fear, count: 2},
{publisher: New Age Books, title: Sushi Anyone?, count: 1},
{publisher: Binnet & Hardley, title: The Gourmet Microwave, count: 1},
{publisher: Binnet & Hardley, title: Silicon Valley, count: 1},
{publisher: Binnet & Hardley, title: Life Without Fear, count: 1},
{publisher: Algodata Infosystems, title: But Is It User Friendly?, count: 3} 

我的解决方案是这样的:

query_set.values('publisher', 'title').annotate(count=Count('title'))

但是没有产生期望的结果。

Answer 1

在Django中有一个特性，如果没有.order_by()子句，将不会对值执行GROUP BY。因此，您可以添加一个.order_by()子句，并使用

处理它:

query_set.values('publisher', 'title').annotate(
count=Count('pk')
).order_by('publisher', 'title')

通过对项目进行排序"到一个组中，因此我们计算每个组的主键的个数。