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[英]Django ORM: How to use count method inside values_list method?
[英]Use django count or values_list counter, which is better?
我寫了一個導出數據的視圖,我的模型是這樣的:
class Event(models.Model):
KIND_CHOICES = (('doing', 'doing'),
('done', 'done'),
('cancel', 'cancel'))
created_at = models.DateTimeField(auto_now_add=True)
created_by = models.ForeignKey('auth.User')
kind = models.CharField(max_length=20, choices=KIND_CHOICES)
事件是三種中的一種,每個用戶每月可能有3~10個事件,首先我查詢本月的事件:
events_this_month = Event.objects.filter(created_at__year=2013,
created_at__month=5)
然后找到所有用戶:
users = User.objects.all()
我導出這樣的數據:
for user in users:
# 1000 users with 5 events each
user_events = events_this_month.filter(created_by=user)
doing_count = user_events.filter(kind='doing').count()
done_count = user_events.filter(kind='done').count()
cancel_count = user.events.filter(kind='cancel').count()
append_to_csv([user.username, doing_count, done_count, cancel_count])
然后我嘗試使用collections.Counter
,我認為這將減少計數SQL次數(實際上它從3000+減少到1200):
for user in users:
user_events = events_this_month.filter(created_by=user)
counter = Counter(user_events.values_list('kind', flat=True))
doing_count = counter['doing']
done_count = counter['done']
cancel_count = counter['cancel']
...
哪種方式更好 ?
就是一個更地道的方式,更有效牙縫算這樣的數據?
這不是測試,但這個想法是由一群user
,然后按組kind
:
from django.db.models import Count
events_this_month = Event.objects.values('created_by', 'kind') \
.filter(created_at__year=2013, created_at__month=5) \
.annotate(cc=Count('kind'))
讓我知道這是否有效,因為我沒有測試過這個。
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