php poo connection

<?php
class Connection{
    public $host;
     public $user;
     public $psw;
     public $db;
    public $sql;

   
    public function Connect(){       
       return mysqli_connect($this->host, $this->user, $this->psw, $this->db);
    }
 
    public function Query(){
        return mysqli_query($this->Connect(),$this->sql);
    }
   
    public function Total(){
        return mysqli_num_rows($this->Query());
    }
   
    public function Fetch(){
        return mysqli_fetch_assoc($this->Query());
    }
 
   
}

$conn=new Connection;
$conn->host="localhost";
$conn->user="root";
$conn->psw="usbw";
$conn->db="si";
$conn->sql="select * from users";
$f=$conn->Fetch();
echo $f['username'];



?>