PDO with Singleton cannot access private property

问题

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?

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` = ?");

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);
    }
}

回答1:

You don't need to write

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

Here you have a reference of your DB class

$db = Database::getInstance();

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

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.

回答2:

Oh, I can't stand all that static struggle no more.

Here is a minified version of @nikic's static PDO class

class DB
{
    protected static $instance = null;

    final private function __construct() {}
    final private function __clone() {}

    public static function instance()
    {
        if (self::$instance === null)
        {
            $dsn = 'mysql:host='.DB_HOST.';dbname='.DB_NAME;
            self::$instance = new PDO($dsn, DB_USER, DB_PASS);
            self::$instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        }
        return self::$instance;
    }
    public static function __callStatic($method, $args) {
        return call_user_func_array(array(self::instance(), $method), $args);
    }
}

Used the way static classes ought to be

echo DB::query("SELECT 'foo'")->fetchColumn();
echo DB::lastInsertId();

Without this __callStatic() magic you will have to mirror all the PDO methods manually, just like ComFreek said.

来源：https://stackoverflow.com/questions/20101082/pdo-with-singleton-cannot-access-private-property

标签

php

pdo

singleton