如何在Django中计数和显示关系ManyToMany中的对象

Question

我有一个包含新闻和分类的简单模型：

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()

我想要计算每个类别的新闻，并将其显示在网站上，如下所示：

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

我该怎么做呢？？

谢谢!

Answer 1

查看Django 1.1中的annotate()函数。

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

示例(来自上面的URL )：

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

Answer 2

非常简单：

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