Double Dependency Injection?

[Whiskas]

		$_SESSION[user] = $userService->getUser(); 
	

A session entry is a serialized piece of data, which cannot hold any resource variables.

Thanks this is the thing I needed to know. I was wrongly thinking that mysqli object was the main problem.

read the stuff you need every time a user opens the page, so you don't have any out-of-sync data.

I wanted to make global user class object that would have functions (with mysql queries) returning appropriate data.

Like $user->getSomething(); and it would return information from the database about that something (groups this user belongs etc).

So, now my problem is finding a way to make global object.
Attempt:

index.php

		global $user;

if (isset($user)) {
    header("Location: home.php");
}

if (isset($_POST['btn-login'])) {

    $userService = new UserService($mysqli, $_POST['identity_number'], $_POST['password']);
    if ($userService->login()) {
        $user = $userService->getUser();
        header("Location: home.php");
    }
} 
	

home.php

		global $user;

if (!isset($user))
    header("Location: index.php"); 
	

After moving to home.php variable $user isn't set..

Reading most comments over this problem directs to Singleton Pattern, but personally I have no clue, how to pass parameters to the instance, so it could contain $id, $name etc.

		class Singleton {
    private static $instance;

    private function __construct() {}
    private function __clone() {}

    public static function getInstance() {
        if (!Singleton::$instance instanceof self) {
             Singleton::$instance = new self();
        }
        return Singleton::$instance;
    }

    public function DoSomething() {
        ...
    }
} 
	

Any known sollution to make class object globl score?

Thanks again for your help.

EDIT:

I found sollution:

		<?php

/**
 * Created by PhpStorm.
 * User: Meh
 * Date: 20.11.2016
 * Time: 12:51
 */
class DB extends MySQLi {
    private static $instance = null ;

    private $host = 'localhost';
    private $user = "root";
    private $password = "Wilki0101";
    private $database = "mydb";

    public function __construct($host, $user, $password, $database){
        parent::__construct($host, $user, $password, $database);
    }

    public static function getInstance(){
        if (self::$instance == null){
            self::$instance = new self('localhost', "user", "pass", "db");
        }
        return self::$instance ;
    }
}	

Now, when the Class user needs to make queries, it just get's an instance like that:

		include "DB.php";

class User
{
    //private static $instance;
    public $_id;
    public $_name;
    public $_lastname;
    public $_groupID;
    public $_subgroupID;
    protected $_db;

    public function __construct($id, $name, $lastname, $groupID, $subgroupID)
    {
        $this->_id = $id;
        $this->_name = $name;
        $this->_lastname = $lastname;
        $this->_groupID = $groupID;
        $this->_subgroupID = $subgroupID;
    }

    public function __toString()
    {
        return $this->_name . " " . $this->_lastname;
    }

    public function getUserGroups()
    {
        $this->_db = DB::getInstance();

        $result = $this->_db->query("select p.idpodgrupy, p.nazwapodgrupy from podgrupy p
                                join grupy_podgrupy g
                                on p.idpodgrupy=g.idpodgrupy
                                join grupy gp
                                on gp.idgrupy = g.idgrupy
                                join uzytkownicy u
                                on u.idgrupy = gp.idgrupy
                                where u.iduzytkownika = 16");

        print_r($result);    
    }
} 
	

And the $results aren't empty.

Thanks anyway kung for your tip with $_SESSION!