Question

<?
class DbConn {
    const DB_HOST = 'localhost';
    const DB_USER = 'root';
    const DB_PASS = 'pw';
    const DB_NAME = 'db';

    static private $instance = NULL;
    private $_db;

    static function getInstance()
    {
      if (self::$instance == NULL)
      {
        self::$instance = new DbConn();
        if(mysqli_connect_errno()) {
            throw new Exception("Database connection failed: ".mysqli_connect_error());
        }
      }
      return self::$instance;
    }

    private function __construct()
    {
        $this->_db = new mysqli(self::DB_HOST, self::DB_USER, self::DB_PASS, self::DB_NAME) or die('Couldnt connect');
    }

    private function __clone() {}

}

DbConn::getInstance()->query();

?>

Im just learning and know I’ve got to singleton pattern, I tried to make my own DBConnect class using singleton, but when I’m trying executing it, it gives an error when calling DbConn::getInstance()->query(); saying that Call to undefined method DbConn::query() What am I doing wrong?

Answer 1

Try adding the following after the __construct function

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

then try

DbConn::getInstance()->query("SELECT * FROM Table"); //Replace your sql