class - OOP PHP + PDO - Is this how it should be? -

i'm trying create simple example class before start implementing following projects , know if there could/should improve. glad if gives me input of how doing now.

simple class example:

  // define class   class user{   private $userid;   private $username;   private $email;    function setuserid($newuserid){     $this -> userid = $newuserid;     }    function getuserid(){     return $this -> userid;     }    function setusername($newusername){     // update object     $this -> username = $newusername;     }     function getusername(){     return $this -> username;     }    function setemail($newemail){     $this -> email = $newemail;               }     function getemail(){     return $this -> email;     }    public function saveuser(){     // check if user exists     $user = new user();     if ($user->userexists($this->userid)){       // user exists - update him       $pdo = new pdo('mysql:host=localhost;dbname=cms;charset=utf8', 'xxx', 'xxx');         $query = $pdo->prepare("update user set username = :username, email = :email, userid = :userid userid = :userid");       $query->bindvalue(':username', $this->username);       $query->bindvalue(':email', $this->email);       $query->bindvalue('userid', $this->userid);       $query->execute();       $pro = null;       }     else{       // insert new       $pdo = new pdo('mysql:host=localhost;dbname=cms;charset=utf8', 'xxx', 'xxx');         $query = $pdo->prepare("insert user (username, email) values (:username, :email)");       $query->bindvalue(':username', $this->username);       $query->bindvalue(':email', $this->email);       $query->execute();       // close connection       $pdo = null;        }     }    private function userexists($userid){     // returns true if users exists, false if not     $pdo = new pdo('mysql:host=localhost;dbname=cms;charset=utf8', 'root', 'vertrigo');     $query = $pdo->prepare("select * user userid=:userid");      $query->bindvalue(':userid', $userid);     $query->execute();     $row = $query->fetch(pdo::fetch_assoc);     $pdo = null;      // user     if ($row){       return true;       }     else{       return false;       }     }           }  function getuserinfo($userid){   // open pdo   $pdo = new pdo('mysql:host=localhost;dbname=cms;charset=utf8', 'root', 'vertrigo');     $query = $pdo->prepare("select * user userid=:userid");   $query->bindvalue(':userid', $userid);   $query->execute();   $row = $query->fetch(pdo::fetch_assoc);   $pdo = null;    // userinfo   $userinfo = new user();   $userinfo -> setuserid($userid);   $userinfo -> setusername($row["username"]);    $userinfo -> setemail($row["email"]);     // return userinfo   return $userinfo;   } 

this basic example of how work it. think should improve?

any php application have connect database once.
thus, class have use created connection, not create every time.

class user{   private $userid;   private $username;   private $email;   private $db;    function __construct($pdo) {     $this->db = $pdo;   }    private function userexists($userid)   {     $sql = "select 1 user userid=?";     $stm = $this->db->prepare($sql);     $stm->execute(array($userid));     return $stm->fetchcolumn();     }           }   // rest going use same approach }  $pdo = //see pdo tag wiki theproper  example  $user = new user($pdo); if ($user->userexists($userid)) {   // whatever }