/**
  * Return composite product type Ids
  *
  * @return array
  */
 public static function getCompositeTypes()
 {
     if (is_null(self::$_compositeTypes)) {
         self::$_compositeTypes = array();
         $types = self::getTypes();
         foreach ($types as $typeId => $typeInfo) {
             if (array_key_exists('composite', $typeInfo) && $typeInfo['composite']) {
                 self::$_compositeTypes[] = $typeId;
             }
         }
     }
     return self::$_compositeTypes;
 }