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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