Django：通過計數排序的聚集輸出聚合

Question

我試圖在我的Django模板中輸出以下數據。

國家將按照故事排列順序排列。 城市將被勒令故事＃下降（該國下）

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) 

什麼是最簡單的方法是什麼？

Answer 1

此解決方案適用於我。你需要調整它才能將它傳遞給模板。

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

這裏是將這些信息發送到模板的一種方式。這一個涉及使用自定義過濾器。

@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

變異與模型的自定義方法。

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) 

這可以讓您避免定義過濾器。模板代碼更改爲：

{% 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 %}