Unlimited Categories Implementation by Recursively

1. MySQL Table Definition:

   CREATE TABLE `categories` (
     `id` int(10) unsigned NOT NULL auto_increment,
     `name` varchar(50) NOT NULL,
     `parent_id` int(10) unsigned zerofill NOT NULL,
     `type` int(10) unsigned zerofill NOT NULL default '0',
     PRIMARY KEY  (`id`)
   ) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=utf8;

2. Implementation for DataObject

   public static function get_all($type = NULL, $parent_id = 0, $depth = 3, $count = 0){
       if($count == $depth) return;
       $condition = is_int($type) ? "AND type=$type" : '';
       
       $categories = Database::instance()->query("SELECT * FROM categories WHERE parent_id = '$parent_id' $condition")->result_array(FALSE);
   
       if(count($categories) == 0) return NULL;
       foreach ($categories as &$category) {
           $category['parent_id'] = intval($category['parent_id']);
           $category['type'] = intval($category['type']);
           $subcategories = self::get_all($type, $category['id'], $depth, $count+1);
           if($subcategories) $category['subcategories'] = $subcategories;
       }
       
       return $categories;
   }

3. Implementation for Logical UI

   public static function output_options($categories,  $depth = 2, $level = 0, $nest = 0){
       if($nest == $depth || !is_array($categories)) return '';
   
       $html = '';
       foreach($categories as $category){
           $html .= "<option value=\"{$category['id']}\"";
           if($nest < $level) $html .= ' disabled="disabled"';
           $html .= '>';
           for($i=0,$j=$nest;$i<$j;$i++) $html .= '　';
           $html .= "{$category['name']}</option>\n";
   
           if(isset($category['subcategories'])) {
               $html .= self::output_options($category['subcategories'], $depth, $level, $nest+1);
           }
       }
       return $html;
   }

4. Usage

   $categories = category::get_all(0,0,2); // All Type, Parent Id = 0, MaxDepth = 2
   echo category::output_options($categories, 2);