django-bit-category 0.2

Django category app which uses tree-like structure using bitwise primary key.

Author:

Tomas Peterka

licence:

GPL

django-bit-category

Abstract (and one concrete) Model with tree-like structure using bitwise ID field. This implementation is very simple and super fast! Given a category, you can query for related models (products) to the category and all it’s subcategories by SomeModel.objects.filter(category_id__gte=category.gte, category_id__lt=category.lt)

The key idea is to reserve a block of bits in model’s ID for different levels of hierarchy. In the basic setup we expect 32 bit ID (can be changed via ID_BIT_WIDTH) and we give 5 bits for each level (can be changed via LEVEL_BIT_WIDTH). The IDs looks like this:

XXXXX000000000000000000000000000  # mask for the root category
00001000000000000000000000000000  # first root
00010000000000000000000000000000  # second root
00011000000000000000000000000000  # third root

00001000010000000000000000000000  # first child of the first root
00001000100000000000000000000000  # second child of the first root

...and so on

Getting all descendants in all levels is in hierarchical_instance.descendants, but under the hood it is as simple as:

SomeModel.objects.filter(category_id__gte=category.gte, category_id__lt=category.lt)

What is included in this app

• abstract HierarchicalModel which takes care about the magic with IDs

• abstract BaseCategory which contains the most usual category implementation

• HierarchicalField which you can use for any custom model

• HierarchicalWidget which dynamically (via AJAX) creates / deletes select boxes

• urls.py and views.py which contains AJAX magic for form field working

How to make it work

If you want to use just a abstract model, then you don’t need to do anything special. Just import a model from bitcategory.models import BaseCategory and here you are.

If you would like to have the awesome dynamic select boxes you need to do more

• add the bitcategory into your INSTALLED_APPS

• add bitcategory.urls into your urls and specify your custom hierarchical model. If you didn’t make custom model, then you still have to specify bitcategory.models.Category. The most simple way looks like:

  # :file: urls.py
  from django.conf.urls import patterns, include, url
  from myapp.models import YourHierarchicalModel
  
  urlpatterns = patterns('',
        url('', include('bitcategory.urls'), {"model": YourHierarchicalModel}),
  )

And that’s done. Just use bitcategory.fields.HierarchicalField and don’t forget to include {{form.media}} into your template for javascripts.

Future:

• [DONE] Adding widget which handles the tree structure via many selects created via AJAX

• Finish the implementation of namespaceses (even in the Field) for different models