<?php

class Database extends MySQLi
{
    private $host, $user, $pass, $name;
    private $connection, $result;

    public function __construct($host, $username, $password, $dbname)
    {
        $this->host = $host;
        $this->user = $username;
        $this->pass = $password;
        $this->name = $dbname;

        $this->_connect();
    }

    private function _connect()
    {
        $this->connection = new MySQLi($this->host, $this->user, $this->pass, $this->name);
    }

    public function query($sql)
    {
        $this->result = $this->connection->query($sql);
        return $this;
    }

    public function fetchAll()
    {
        $obj = new stdClass();

        while($fetch = $this->result->fetch_object())
        {
            $obj = $fetch;
        }

        return $obj;
    }
}

$db = new Database('localhost', 'root', '', 'test_db');
$db->query("SELECT * FROM `tabelle`)->fetchAll();