PHP: Convert 'Adjacency List Model' database to a 'Nested Set Model' database

rebuild_tree.php

<?php

	rebuild_tree(1, 1);

	function rebuild_tree($parent_id, $left) {

		// The right value of this node is the left value + 1
		$right = $left+1;

		// Get all children of this node
		$this->db->select('id');
		$this->db->from('geo');
		$this->db->where('parent_id', $parent_id);
		$result = $this->db->get();

		foreach ($result->result() as $row) {
			$right = $this->rebuild_tree($row->id, $right);
		}

		// We've got the left value, and now that we've processed
		// the children of this node we also know the right value
		$this->db->where('id', $parent_id);
		$this->db->update('geo', array('lft' => $left, 'rgt' => $right)); 

		// Return the right value of this node + 1
		return $right+1;

	}