categories.php

<?php
/**
 * Copyright (c) 2009, Ionut Gabriel Stan. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *    * Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *    * Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @author    Ionut G. Stan <ionut.g.stan@gmail.com>
 * @license   New BSD license
 * @copyright Copyright (c) 2009, Ionut Gabriel Stan. All rights reserved.
 */

/**
 * Each element in the return array has a 'data' key, holding category data,
 * like name, and a 'children' key holding its subcategories.
 *
 * @param  resource $resource      MySQL resource resulted from mysql_query
 * @param  string   $id_key        Name of the 'id' field
 * @param  string   $parent_id_key Name of the 'parent_id' field
 * @param  boolean  $use_cache     Use cached result from previous calls. Defaults to TRUE
 * @return array
 */
function categories($resource, $id_key, $parent_id_key, $use_cache = true) {
    // Cache the categories in a static local variable. This way, the query
    // will be executed just for the first function call. Subsequent calls
    // will return imediatelly, unless you tell it not to.
    static $tree = array();

    if ($tree && $use_cache) {
        return $tree;
    }
    
    // Flat representation of the categories for fast retrieval using array
    // keys. Each element will be referenced in the $tree array. This
    // allows to build a tree data structure using a flat one.
    $flat = array();
    
    // Reset the $tree, in case $use_cache=false in a subsequent call
    $tree = array();

    while ($row = mysql_fetch_object($resource)) {
        $flat[$row->$id_key] = array(
            'data'     => $row,
            'children' => array(),
        );

        if (array_key_exists($row->$parent_id_key, $flat)) {
            // Assign children by reference so that possible subcategories of
            // this one will appear in the tree structure ($tree)
            $flat[$row->$parent_id_key]['children'][] =& $flat[$row->$id_key];
        }

        if ($row->$parent_id_key == 0) {
            // Assign by reference for synchronizing $flat with $tree;
            $tree[] =& $flat[$row->$id_key];
        }
    }

    return $tree;
}