如何关闭扩展类的连接

Question

我有一个单例数据库连接类-db.php（通过谷歌搜索找到）：

<?php
/*
* Mysql database class - only one connection alowed
*/
class db {
    private $_connection;
    private static $_instance; //The single instance
    private $_host = "localhost";
    private $_username = "user_name";
    private $_password = "password";
    private $_database = "database";

    /*
    Get an instance of the Database
    @return Instance
    */
    public static function getInstance() {
        if(!self::$_instance) { // If no instance then make one
            self::$_instance = new self();
        }
        return self::$_instance;
    }

    // Constructor
    private function __construct() {
        $this->_connection = new mysqli($this->_host, $this->_username,
            $this->_password, $this->_database);

        // Error handling
        if(mysqli_connect_error()) {
            trigger_error("Failed to conencto to MySQL: " . mysql_connect_error(),
                 E_USER_ERROR);
        }

    // Magic method clone is empty to prevent duplication of connection
    private function __clone() { }

    // Get mysqli connection
    public function getConnection() {
        return $this->_connection;
    }

    public function closeConnection(){
      $this->_connection->close();
    }
}
?>

为了测试连通性，如果我像这样在 ext.php 中扩展该数据库类：

<?php
class ext extends db {
private $conn;
function __construct(){
 $this->connect();
 if(isset($this->conn)){
       echo 'Connection is established<br />';
  }
 $this->closeConn();
}
public function connect(){ 
    $this->conn = parent::getInstance()->getConnection();
}
public function closeConn(){
     parent::closeConnection();
}
}
?>

在我的 index.php 页面中：

<?php
spl_autoload_register(function ($class) {
    include '../classes/' . $class . '.php';
});
$test = new ext();
?>

现在我的输出如下：

Connection is established 
Fatal error: Call to a member function close() on a non-object in (line number) of db.php

我的问题是如何关闭扩展类 (ext.php) 中的连接？

Answer 1

解决方案是这样的：

• 首先，在ext类中创建父类db的private实例变量，如下所示：

  class ext extends db {
      ...
      private $parentInstance;
      ...
  }
  

• 然后使用此实例变量$parentInstance 来创建和关闭您的连接，如下所示：

  class ext extends db {
      private $conn;
      private $parentInstance;
      function __construct(){
          $this->connect();
          if(isset($this->conn)){
              echo 'Connection is established<br />';
          }
          $this->closeConn();
      }
      public function connect(){ 
          $this->parentInstance = parent::getInstance();
          $this->conn = $this->parentInstance->getConnection();
      }
      public function closeConn(){
           $this->parentInstance->closeConnection();
      }
  }
  

---

旁注：db 类中也有一个小的语法错误。构造方法的右括号丢失。