具有Singleton的PDO无法访问私有财产 [英] PDO with Singleton cannot access private property

问题描述

我已经与PDO和单例模式建立了数据库连接. 只要将$_db变量设置为public，一切都可以正常工作，但是它必须是私有的.当我将它设为私有时，我当然会得到错误:无法访问私有属性Database :: $ _ db 有人可以告诉我如何将其设为私有并仍然能够获得实例吗?

I´ve made a database connection with PDO and the singleton pattern. Everything works fine as long as I have the $_db variable set as public but it needs to be private... When I make it private I off course get the Error: Cannot access private property Database::$_db Can someone tell me how to make it private and still be able to get an instance?

当我从另一个文件调用数据库连接时，我调用函数getInstance() 这是我从一个文件中调用它的示例:

When I call the database connection from another file I call the function getInstance() Here is an example how I call it from one file:

$db = Database::getInstance();
$query = $db->_db->prepare("SELECT `password`, `id` FROM `users` WHERE `username` = ?");     

这是我的数据库连接文件的样子:

This is what my database connection file looks like:

class Database 
{
    private $_db;
    static $_instance;

    private function __construct() 
    {
        $this->_db = new PDO('mysql:host=localhost;dbname=mvcuser', 'root', '');
        $this->_db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    private function __clone(){}

    public static function getInstance() 
    {
        if (!(self::$_instance instanceof self)) 
        {
            self::$_instance = new self();
        }
        return self::$_instance;
    }

    public function query($sql) 
    {
    return $this->_db->query($sql);
    }
}

推荐答案

您不需要写

You don't need to write

$ db-> _ db->
因为您已经在使用类的实例.

$db->_db->
Because you're already using instance of your class.

这里有您的数据库类的引用

Here you have a reference of your DB class

$db = Database::getInstance();

每次决定进行查询或填充时仅使用$db->query();, $db->prepare();

Every time when you decide to make a query or someting use only $db->query();, $db->prepare();

查看您的代码:您已经在$ DB类中使用$ _db引用. 因此，您无需将$ _db称为公共变量.

Look at your code: you're already using $_db reference in you DB class. So, you don't need to call $_db as public variable.

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