Django：按计数排序的聚合的输出聚合

Question

我正在尝试在 django 模板中输出以下数据。

国家/地区将按故事数量降序排列。 城市将按故事数量降序排列（在该国家/地区下）

Country A(# of stories)
  City A (# of stories)
  City B (# of stories)

Country B(# of stories)
  City A (# of stories)
  City B (# of stories)

我的模型如下：

# Create your models here.
class Country(models.Model):
    name = models.CharField(max_length=50)

class City(models.Model):
    name = models.CharField(max_length=50)
    country = models.ForeignKey(Country)

class Story(models.Model):
    city = models.ForeignKey(City)
    country = models.ForeignKey(Country)
    name = models.CharField(max_length=255)

最简单的方法是什么？

Answer 1

这个解决方案对我有用。不过，您需要对其进行调整以将其传递给模板。

from django.db.models import Count
all_countries = Country.objects.annotate(Count('story')).order_by('-story__count')

for country in all_countries:
    print "Country %s (%s)" % (country.name, country.story__count)
    all_cities = City.objects.filter(country = country).annotate(Count('story')).order_by('-story__count')
    for city in all_cities:
        print "\tCity %s (%s)" % (city.name, city.story__count)

更新

这是将此信息发送到模板的一种方法。这涉及到使用自定义过滤器。

@register.filter
def get_cities_and_counts(country):
    all_cities = City.objects.filter(country = country).annotate(Count('story')).order_by('-story__count')
    return all_cities

查看：

def story_counts(request, *args, **kwargs):
    all_countries = Country.objects.annotate(Count('story')).order_by('-story__count')
    context = dict(all_countries = all_countries)
    return render_to_response(..., context)

在您的模板中：

{% for country in all_countries %}
    <h3>{{ country.name }} ({{ country.story__count }})</h3>
    {% for city in country|get_cities_and_counts %}
        <p>{{ city.name }} ({{ city.story__count }})</p>
    {% endfor %}
{% endfor %}

更新 2

模型中具有自定义方法的变体。

class Country(models.Model):
    name = models.CharField(max_length=50)

    def _get_cities_and_story_counts(self):
        retrun City.objects.filter(country = self).annotate(Count('story')).order_by('-story__count')
    city_story_counts = property(_get_cities_and_story_counts)

这可以让您避免定义过滤器。模板代码改为：

{% for country in all_countries %}
    <h3>{{ country.name }} ({{ country.story__count }})</h3>
    {% for city in country.city_story_counts %}
        <p>{{ city.name }} ({{ city.story__count }})</p>
    {% endfor %}
{% endfor %}