Question

我认为这不应该很复杂，但是我做不到。

如何有条件地计算查询集中特定类别中的品牌数量？

views.py

def get_brands(request):

    all_brands = brand.objects.values('brand_name','brand_category').\
            annotate(brand_proportion=Count('brand_name')/Count('brand_name',
            filter=Q(brand_category="brand_category"))#I'm stuck here

    return JsonResponse(list(all_brands), safe=False)

我不确定要筛选品牌类别并计算其中的品牌数量类别。

For example: 

brand_category 'A' might have: Brand 1,Brand 1 ,Brand 1,Brand 2,Brand 2

Here, the proportion of Brand 1 in category A would be 3/5 = 0.6  or 60%

I can calculate the 3 using Count('brand_name') within the queryset, but how can i calculate 
the 5?

brand_category 'B' might have: Brand 1,Brand 2,Brand 3,Brand 4,Brand 5

Here, the proportion of Brand 1 in category B would be 1/5 = 0.2 or 20%

Answer 1

关于django doc。

from django.db.models import Count

q = Book.objects.annotate(num_authors=Count('authors'))
total_authors = som([x.num_authors for x in q])

所以我希望我成功了。

动态注释和过滤

1 个答案: