Django multi level reverse lookup - django

Question

I have a site where the items are classified by categories and subcategories. My models look like this:
from django.db import models
class Category(models.Model):
name = models.CharField(max_lenght=100)
class Subcategory(models.Model):
name = models.CharField(max_lenght=100)
category = models.ForeignKey('Category')
class Item(models.Model):
name = models.CharField(max_lenght=100)
subcategory = models.ForeignKey('Subcategory')
I need to display all the items of one category and all the subcategories with the items in the same page (it's a requisite of the project) and the lists should be in order, like this:
Category:
Item 1
Item 2
Item 3
Item 4
Item 5
Item 6
Subcategory 1
Item 1
Item 3
Item 4
Subcategory 2
Item 2
Item 5
Item 6
So far I have two possible queries but I can't get this done.
items = Item.objects.prefetch_related('subcategory', 'subcategory__category').filter(subcategory__category__slug=categorySlug)
This query gives me a QuerySet and I can do a for loop in my template to show all the items but I can't order them by subcategory.
{% for item in items %}
What I need is something like for subcategory in items.subcategory.
The next query is the inverse:
category = Category.objects.prefetch_related('subcategory_set', 'subcategory_set__item_set').get(slug=categorySlug)
With this query I can do a loop to show the items by subcategory
{% for subcategory in category.subcategory_set.all %}
{% for item in subcategory.item_set.all %}
What I can't do is to display all the items in order by category. I need something like for item in category.subcategory_set__item_set.all or for item in category.subcategory_set.all.item_set.all
I am aware that I can do it using multiple queries (in fact using the two queries at the same time), but I'm trying to use a single query to do this job. Is it possible?

Answer 1

You can just take a list of subcategories and use regroup
{% regroup subcategories by category as subcat_list %}
<ul>
{% for sub_cat in subcat_list %}
<li>{{ sub_cat.grouper }}
<ul>
{% for item in sub_cat.list %}
<li>{{ item.name }}</li>
{% endfor %}
</ul>
</li>
{% endfor %}
Can you do it with a single query? Not really since you need one to iterate over all subcategories and then another to for the categories to produce the first part of your list