Forum Categories MPTT for CodeIgniter 4

A modern Modified Preorder Tree Traversal (MPTT) implementation for managing hierarchical forum categories in CodeIgniter 4.

This library is designed to be a forward-thinking replacement for traditional adjacency lists by providing:

• Efficient read operations (descendants, siblings, paths)
• Full create, move, copy, delete operations with transactional safety
• Soft deletes and hard deletes
• Tree integrity checks and a rebuild method for recovery
• Integrated CodeIgniter caching to minimize database queries
• Easy UI helpers (toList(), toSelect())

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🚀 Features

• Add nodes anywhere in the tree (root, child, sibling)
• Move or copy entire subtrees
• Retrieve descendants, siblings, and parent relationships
• Soft deletes (delete()) and permanent deletes (hardDelete())
• verifyTree() to check consistency of the tree
• rebuildTree() to restore a broken hierarchy
• Caching via CodeIgniter’s cache drivers (APCu, Redis, File, etc.)

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📦 Installation

Copy the class file into your application:

app/Libraries/CategoryMPTT.php

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🗄️ Database Schema

Example schema for the forum_categories table:

CREATE TABLE `forum_categories` (
  `id` INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  `name` VARCHAR(255) NOT NULL,
  `slug` VARCHAR(255) NOT NULL,
  `parent_id` INT UNSIGNED DEFAULT NULL,
  `lft` INT UNSIGNED NOT NULL,
  `rgt` INT UNSIGNED NOT NULL,
  `depth` INT UNSIGNED NOT NULL DEFAULT 0,
  `created_at` DATETIME DEFAULT CURRENT_TIMESTAMP,
  `updated_at` DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `deleted_at` DATETIME DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

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⚙️ Usage

Load the library

use App\Libraries\CategoryMPTT;

$mptt = new CategoryMPTT();

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Add Categories

// Root category
$programmingId = $mptt->add([
    'name' => 'Programming',
    'slug' => 'programming'
]);

// Child category under Programming
$phpId = $mptt->add([
    'name' => 'PHP',
    'slug' => 'php'
], $programmingId, 'lastChild');

// Another child category
$ci4Id = $mptt->add([
    'name' => 'CodeIgniter 4',
    'slug' => 'codeigniter-4'
], $phpId, 'lastChild');

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Move or Copy Nodes

// Move "CodeIgniter 4" under "Programming"
$mptt->move($ci4Id, $programmingId, 'lastChild');

// Copy "PHP" subtree under "Programming"
$newPhpId = $mptt->copy($phpId, $programmingId, 'lastChild');

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Delete Categories

// Soft delete (marks as deleted_at)
$mptt->delete($phpId);

// Hard delete (removes node + descendants, adjusts tree)
$mptt->hardDelete($ci4Id);

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Retrieve Information

// Get all descendants of "Programming"
$children = $mptt->getDescendants($programmingId);

// Get parent of "CodeIgniter 4"
$parent = $mptt->getParent($ci4Id);

// Get siblings of "PHP"
$siblings = $mptt->getSiblings($phpId);

// Breadcrumb path for "CodeIgniter 4"
$path = $mptt->getPath($ci4Id);

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UI Helpers

// Generate <ul>/<li> list
echo $mptt->toList();

// Generate <select> options with indentation
$options = $mptt->toSelect();

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Tree Integrity

// Verify tree consistency
if (! $mptt->verifyTree()) {
    echo "Tree is broken!";
}

// Rebuild tree if necessary
$mptt->rebuildTree();

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🧪 Caching

This library uses CodeIgniter’s caching system.

• Default cache key: categories_tree
• Default TTL: 300 seconds
• Cache is automatically invalidated after write operations.

You can configure cache drivers in app/Config/Cache.php.

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🛡️ Transactions

All write operations (add, move, delete, hardDelete, copy, update, rebuildTree) run inside InnoDB transactions for data integrity.

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📌 Example: Rendering a Category Select

$mptt = new CategoryMPTT();
$options = $mptt->toSelect();

echo '<select name="category_id">';
foreach ($options as $id => $label) {
    echo "<option value='{$id}'>{$label}</option>";
}
echo '</select>';

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📌 Example: Breadcrumb Navigation

$path = $mptt->getPath($ci4Id);

echo '<nav aria-label="breadcrumb"><ol class="breadcrumb">';
foreach ($path as $node) {
    echo "<li class='breadcrumb-item'>{$node['name']}</li>";
}
echo '</ol></nav>';

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✅ Summary

This MPTT library gives you:

• Fast reads for hierarchical forum categories
• Safe writes with transactions
• Flexibility with soft/hard deletes
• Recovery tools for rebuilding corrupted trees
• CI4 caching to minimize database hits

Perfect for forums, blogs, menus, product categories, and any nested data structure.

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📋 Requirements

• PHP 8.1+
• CodeIgniter 4.5+
• MySQL 8.0+ (InnoDB engine recommended)

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📜 License

This project is open-sourced software licensed under the MIT license.

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