Django 3 Web Development Cookbook - Fourth Edition

How it works...

The MPTTModel mixin will add the tree_id, lft, rght, and level fields to the Category model:

• The tree_id field is used as you can have multiple trees in the database table. In fact, each root category is saved in a separate tree.
• The lft and rght fields store the left and right values used in the MPTT algorithms.
• The level field stores the node's depth in the tree. The root node will be level 0.

Through the order_insertion_by meta option specific to MPTT, we ensure that when new categories are added, they stay in alphabetical order by title.

Besides new fields, the MPTTModel mixin adds methods to navigate through the tree structure similar to how you navigate through DOM elements using JavaScript. These methods are as follows: ...