获取对模板中过滤的子查询的计数 [英] Get count on filtered subqueries in template
问题描述
如果我有一个父模型和一个子模型,那么我如何可以列出父对象的所有子对象,并为每个子对象设置一个过滤的计数列出他们的时候?
If I have a parent model and a child model, how can I then list all child objects of a parent object, and have a filtered count for each child object, when listing them?
举个例子,假设我们有这些模型:
To give an example, assume we have these models:
class Category(models.Model):
...
class SubCategory(models.Model):
category = models.ForeignKey(Category)
....
class Tag(models.Model):
....
class Article(models.Model)
sub_category = models.ForeignKey(SubCategory)
tag = models.ForeignKey(Tag)
然后我们有一个类别的DetailView,其中列出了该类别的所有子卡。在这个列表中,我们希望对每个子类别条目进行计数,其中包含的文章数量也是一个特定的标签(也就是说,不是所有的 em>这个子类别的文章,这似乎更为微不足道的构建)。这样的东西:
Then we have a DetailView for a Category, in which all SubCatoegories for that Category are listed. In this list, we want to have a count on each SubCategory entry, on the number of articles it contains that also is of a certain tag (that is, not a count on all articles of that SubCategory, which seems much more trivial to build). Something like this:
{% for sub_category in category.sub_category_set.all %}
{{ sub_category.name }} -- {{ sub_category.articles_set.filter(tag='xyz').all|length }}
我想这必须在某些方面在views.py和/或models.py中完成。我只是这样写,以澄清我的意思。那么我该怎么做到这样呢?
I guess this has to be done in the views.py and/or models.py in some way in the end. I just wrote it like this to clarify what I mean. So, how can I achieve something like this?
推荐答案
你是对的,你必须这样做。您可以使用注释获取每个子类别的过滤条目数:
You're right that you'll have to do this in the view. You can use annotation to get the number of filtered articles for each subcategory:
from django.db.models import Count
def my_view(request, other, arguments):
...
subcategories = category.sub_category_set.filter(tag__tagname='xyz') \
.annotate(num_articles=Count('article__id'))
...
通过子类别
到您的模板上下文中,您可以在模板中执行以下操作:
Pass subcategories
to your template context, and in your template you can do this:
{% for subcategory in subcategories %}
{{ subcategory.name }} -- {{ subcategory.num_articles }}
{% endfor %}
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