Django等同于count和group by [英] Django equivalent for count and group by

问题描述

我有一个如下所示的模型：

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)

我想为每个类别选择计数（只是计数）的项目，所以在SQL中这样简单：

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

有没有相当于做这个Django方式？还是纯SQL的唯一选择？我熟悉Django中的 count（）方法，但是我看不到 可以适应那里。

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

正如我刚才发现的那样，Django 1.1聚合API是如何做到的：

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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