php中的PDO類

Question

美好的一天！我有這個問題：

final class Db 
{ 
    /* 
    @ var object of PDO 
    */ 
    private static $connection = FALSE; 

    /* 
    @ database settings 
    */ 
    private static $data = []; 

    private function __construct() 
    { 
     self::$data['host'] = 'localhost'; 
     self::$data['user'] = 'root'; 
     self::$data['pass'] = ''; 
     self::$data['db'] = '123'; 
    } 

    /* 
    @ method connect to PDO 
    */ 
    private static function connect() 
    { 
     if(!isset(self::$connection)) 
     { 
      try 
      { 
       self::$connection = new \PDO('mysql:host='.self::$data['host'].';dbname='.self::$data['db'], self::$data['user'], self::$data['pass']); 
       self::$connection -> setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION); 
       self::$connection -> exec('SET NAMES utf8'); 
      } 
      catch (PDOException $e) 
      { 
       die('Ошибка подключения к БД'); 
      } 
     } 
    } 

    //HERE 
    /* 
    @ method SQL query in database + return array 
    @ param (string) $sql   SQL query 
    @ param (array) $param   Values for execute 
    @ param (const) $const   PDO Constants for tipization 
    @ return (array) 
    */ 
    public function queryFetch($sql, $params = [], $const = PDO::FETCH_ASSOC) 
    { 
     self::connect(); 
     return self::$connection -> prepare($sql)-> execute($params) -> fetch($const); 
    } 

} 

$array = Db::queryFetch('SELECT * FROM `user` WHERE id = ?', ['1']); 
var_dump($array); 

致命錯誤：調用一個成員函數上布爾製備（）在C：\ OpenServer的\ OpenServer的\域\ test1.ru \的index.php上線68
請如果你知道我必須做的，幫助我，這對我來說非常重要

Answer 1

更換if(!isset(self::$connection))到if(!self::$connection)

或更換private static $connection = FALSE;到private static $connection = null;

而且在isset()上閱讀documentation：

isset — Determine if a variable is set and is not NULL