如何做嵌套组与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?

下面是我想做的:我想在单个对象中计算每个作者出版的书的数量。我想得到以下结果:

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

您可以使用groupby(…)对查询结果进行后处理。itertools的函数^[Python-doc]包<一口>[Python-doc]:

from django.db.models import Count
from itertools import groupby
from operator import itemgetter
qs = query_set.values('publisher', 'title').annotate(
count=Count('pk')
).order_by('publisher', 'title')
result = [
{
'publisher': p,
'titles': {r['title']: r['count']for r in rs }
}
for p, rs ingroupby(qs, itemgetter('publisher'))
]