如何在Django中计算和显示与ManyToMany相关的对象

Question

我有一个包含新闻和类别的简单模型：

class Category(models.Model):
    name = models.CharField()
    slug = models.SlugField()

class News(models.Model):
    category = models.ManyToManyField(Category)
    title = models.CharField()
    slug = models.SlugField()
    text = models.TextField()
    date = models.DateTimeField()

我想统计每个类别的新闻，并在网站上显示，如下所示：

Sport (5)
School (4)
Films (6)
Computer (2)
etc...

我怎样才能做到这一点？？

谢谢！

Answer 1

从Django 1.1中检出annotate（）函数。

http://docs.djangoproject.com/en/dev/topics/db/aggregation/#topics-db-aggregation

示例（从上面的URL）：

>>> q = Book.objects.annotate(num_authors=Count('authors'))
>>> q[0].num_authors
2
>>> q[1].num_authors
1

Answer 2

很简单的：

>>> for category in Category.objects.all():
...     print category.name, category.news_set.count()