過濾器在使用循環

Question

查詢集我有inital查詢集和我遍歷這個

stats = {} 
queryset = Item.objects.all() 
for sub in Subject.objects.all(): 
     stats[str(sub.id)] = queryset.filter(subjects=sub.id).count() 

我怎麼能這樣不打DB如此頻繁？

Answer 1

查找django aggregation：

from django.db.models import Count 

stats = Subject.objects.annotate(count=Count('item')) 

現在每個統計對象將有count領域：

stats[0].count 

Answer 2

Subject.objects.values('pk').annotate(total=Count('item'))