mengambil data di databse mengunakan oop

 <?php

class user{

 public function __construct(){
   $this->_db = db::getInstance();

 }

public function register_user($data = array())
{
    if($this->_db->insert('users',$data)) return true;
    else return false;
}

public function login_user($username,$password)
{

    $data = $this->_db->get_info('users', 'username', $username);

    if(password_verify($password,$data['password'])){
      return true;
    }else {
      return false;
    }
}

public function check_nama ($username)
{
    $data = $this->_db->get_info('users','username',$username);
    if( empty($data)) return false;
    else return true;
}

public function level ($user)
{
    $data = $this->_db->get_level('users','username',$user);
    $level = $data['level'];

    if($level == 1) return true;
    else return false;
}

public function ambildata()
{
  $data = $this->_db->get_data('users','username',$user);

  if(        ) return true;
  else return false;
}

}
 ?>

 <?php require_once 'header.php';

$user = session:get('username');
$data = $user->ambildata($user);

 ?>

saya mau bertanya saya bingung logika mengambil data dari database gimana yang di baguan funchtion ambildata