db.class.php

<?php
class DB {

    private $host = 'localhost';
    private $username = 'root';
    private $password = '';
    private $database = 'purpoze';
    private $db;

    public function __construct($host = null, $username = null, $password = null, $database = null){
        if ($host != null){
            $this->host = $host;
            $this->username = $username;
            $this->password = $password;
            $this->database = $database;
        }

        $this->db = new PDO('mysql:host='.$this->host.';dbname='.$this->database, $this->username,
                  $this->password, array(
                      PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES UTF8',
                      PDO::ATTR_ERRMODE => PDO::ERRMODE_WARNING
                  ));

    }

    public function query($sql, $data = array()){
      $req = $this->db->prepare($sql);
      $req->execute($data);
      return $req->fetchall(PDO::FETCH_OBJ);
    }
}