What is Modified Preorder Tree Traversal?

MPTT is a technique for storing hierarchical data in a database. The aim is to make retrieval operations very efficient.

The trade-off for this efficiency is that performing inserts and moving items around the tree is more involved, as there’s some extra work required to keep the tree structure in a good state at all times.

Here’s a good article about MPTT to whet your appetite and provide details about how the technique itself works:

What is django-mptt?

django-mptt is a reusable Django app which aims to make it easy for you to use MPTT with your own Django models.

It takes care of the details of managing a database table as a tree structure and provides tools for working with trees of model instances.

Feature overview

  • Simple registration of models - fields required for tree structure will be added automatically.
  • The tree structure is automatically updated when you create or delete model instances, or change an instance’s parent.
  • Each level of the tree is automatically sorted by a field (or fields) of your choice.
  • New model methods are added to each registered model for:
    • changing position in the tree
    • retrieving ancestors, siblings, descendants
    • counting descendants
    • other tree-related operations
  • A TreeManager manager is added to all registered models. This provides methods to:
    • move nodes around a tree, or into a different tree
    • insert a node anywhere in a tree
    • rebuild the MPTT fields for the tree (useful when you do bulk updates outside of django)
  • Form fields for tree models.
  • Utility functions for tree models.
  • Template tags and filters for rendering trees.
  • Translations for:
    • Danish
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