如何在Django中获得3级对象计数

Question

I'm building a list of sections, categories and subcategories for a small e-market project on Django.

I have a model like this:

Section > Category (FK Section) > SubCategory (FK Category) > ShopProduct (FK SubCategory)

The problem is that I have many of categories (and subcategories) which are empty, and for that reason I filter data in the query set with:

{% if section.shopcategory_set.count > 0 %}

It will filter the sections if there are more than 1 categories assigned to this section. (But it doesn't filter if any items are assigned deeper)

So, I want to count final objects from the first level cycle

Something like:

{% for section in sections %}
    {% if section.category_set.subcategory_set.shopproduct_set.count > 0 %}
    {{ section.name }}
    {% endif %}
{% endfor %}

Answer 1

The general principle is to start from the object you want to retrieve, or in this case count. So, you need to start with ShopProduct and follow the relationships. In a view that would be:

ShopProduct.objects.filter(subcategory__category__section=my_section)

However, you can't do this in the template, because you can't call methods with parameters. So you'd need to define this as a method on the Section class, replacing my_section with self , then you can do (eg) {{ section.get_product_count }} .