Django：通过计数排序的聚集输出聚合

Question

我试图在我的Django模板中输出以下数据。

国家将按照故事排列顺序排列。 城市将被勒令故事＃下降（该国下）

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) 

什么是最简单的方法是什么？

Answer 1

此解决方案适用于我。你需要调整它才能将它传递给模板。

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

这里是将这些信息发送到模板的一种方式。这一个涉及使用自定义过滤器。

@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) 

而且在你的模板：

{% 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

变异与模型的自定义方法。

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。模板代码更改为：

{% 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 %}