public static function getPK()
    {
        $cls = get_called_class();
        return array_key_exists($cls, self::$_pk) ? self::$_pk[$cls] : "id";
    }
public static function getPK()
    {
        $cls = get_called_class();
        return array_key_exists($cls, self::$_pk) ? self::$_pk[$cls] : "id";
    }
public static function getPK ( ) { $ cls = get_called_class ( ) ; return array_key_exists ( $ cls , self :: $ _pk ) ? self :: $ _pk [ $ cls ] : "id" ; }
Returns the primary key column.

@return string primary key
Returns the primary key column .