Django 等价于 count 和 group by [英] Django equivalent for count and group by
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问题描述
我有一个看起来像这样的模型:
I have a model that looks like this:
class Category(models.Model):
name = models.CharField(max_length=60)
class Item(models.Model):
name = models.CharField(max_length=60)
category = models.ForeignKey(Category)
我想要为每个类别选择项目的计数(只是计数),所以在 SQL 中它会像这样简单:
I want select count (just the count) of items for each category, so in SQL it would be as simple as this:
select category_id, count(id) from item group by category_id
是否有类似的Django 方式"?还是纯 SQL 是唯一的选择?我熟悉 Django 中的 count( ) 方法,但是我不知道 group by 将如何适合那里.
Is there an equivalent of doing this "the Django way"? Or is plain SQL the only option? I am familiar with the count( ) method in Django, however I don't see how group by would fit there.
推荐答案
这里,正如我刚刚发现的,是如何使用 Django 1.1 聚合 API 做到这一点:
Here, as I just discovered, is how to do this with the Django 1.1 aggregation API:
from django.db.models import Count
theanswer = Item.objects.values('category').annotate(Count('category'))
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