/**
  * @param string $strName
  * @return QQColumnNode
  * @throws QCallerException
  */
 public function GetVirtualNode($strName)
 {
     $strName = QQ::GetVirtualAlias($strName);
     if (isset($this->objVirtualNodeArray[$strName])) {
         return $this->objVirtualNodeArray[$strName];
     } else {
         throw new QCallerException('Undefined Virtual Node: ' . $strName);
     }
 }