Vil gerne igang med session i mysqli

<?php
// ligger externt da connection skal bruges i flere filer
$db_host = "localhost";
$db_username ="root";
$db_password="";
$db = "test";
$test_database_session = mysqli_connect($db_host, $db_username, $db_password, $db);
if (!$test_database_session) {
    echo 'Der opstod en fejl.';
    exit();
}
mysqli_set_charset($test_database_session, "utf8");
?>

<?php
if(! isset($_SESSION) ){
    session_start();
    $_SESSION['kurv'] = array();    
    
    // test data skal slettes senere
    $_SESSION['kurv']=array(
        "4"=>array("id"=>4, "antal"=>2), 
        "2"=>array("id"=>2, "antal"=>2), 
        "1"=>array("id"=>1, "antal"=>2), 
        "7"=>array("id"=>7, "antal"=>2)
    );
    
}
require_once("connection.php");

foreach($_SESSION["kurv"] as $varer => $vare){ 
    $id = $vare['id'];
    $antal = $vare['antal'];
    $query_rsVarer = "SELECT * FROM tbl_vare WHERE id = ".$id;
    
    
    $rsVarer = mysqli_query($test_database_session, $query_rsVarer) or die(mysqli_error($test_database_session));
    $row_rsVarer = mysqli_fetch_assoc($rsVarer); 
    echo '<br /><a href="slet_en_vare.php?id='.$id.'">Slet</a><br />';
    echo '<br /><a href="slet_antal.php?id='.$id.'">Slet antal</a><br />';
    echo $id;
    echo "<br />";
    echo $id = $row_rsVarer['name'];
    echo "<br />";
    echo "Om varen: ".$row_rsVarer['tekst'];
    echo "<br />";
    echo "Pris: ".$row_rsVarer['pris']." kr.";
    echo "<br />";
    echo "Antal: ".$antal;
    echo "<br />";
    echo "Pris i alt: ".$antal * $row_rsVarer['pris']. " kr. i alt.";
    echo "<br />";
}
?>

---------------------------------

--
-- Database: `test`
--

-- --------------------------------------------------------

--
-- Struktur-dump for tabellen `tbl_vare`
--

CREATE TABLE IF NOT EXISTS `tbl_vare` (
`id` int(11) NOT NULL,
  `name` varchar(255) COLLATE utf8_danish_ci NOT NULL,
  `pris` float NOT NULL,
  `tekst` text COLLATE utf8_danish_ci NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COLLATE=utf8_danish_ci;

--
-- Data dump for tabellen `tbl_vare`
--

INSERT INTO `tbl_vare` (`id`, `name`, `pris`, `tekst`) VALUES
(1, 'sofa0', 12.5, 'brun læder sofa0'),
(2, 'sofa1', 12.5, 'brun læder sofa1'),
(3, 'sofa2', 12.5, 'brun læder sofa2'),
(4, 'sofa3', 12.5, 'brun læder sofa3');

<?php
if(! isset($_SESSION) ){
    session_start();        
}
if(! isset($_SESSION['kurv']) ){
    $_SESSION['kurv'] = array();    
}

if (isset($_POST['action'])) {
    $action = $_POST['action'];
    $id = $_POST['id'];
    switch ($action) {
        case 'add':
            $quantity = $_POST['quantity'];
            $_SESSION['kurv'][$id] = array("id" => $id, "antal" => $quantity);
            break;
        default: break;
    }
}

?>
<!DOCTYPE html>
<html>
<head>
 <meta charset="utf-8">
    <title>demo</title>
    
    <style type="text/css">
    </style>
    <script type="text/javascript">
    
    </script>
</head>
<body>
<?php
require_once("vis_kurv.php");
?>
        alle vare
        <div>
            <span>navn</span>
            <span>beskrivelse</span>
            <span>antal</span>
            <span>pris</span>
            <span>tilføj</span>
        </div>

        <?php
            $str = "";
            $sql ="SELECT * FROM tbl_vare";
            $rs = mysqli_query($test_database_session, $sql) or die(mysqli_error($test_database_session));
            while($row = mysqli_fetch_assoc($rs)){        
            $str.="\n";
            $str.='<div>';
            $str.='<form action="' . $_SERVER['PHP_SELF'] . '" method="post">';
            $id = $row['id'];
            $str.='<input type="hidden" name="id" value="' . $id . '" >';
            $str.='<span>' . $row['name'] . '</span>';
            $str.='<span>' . $row['tekst'] . '</span>';
            $str.='<span><input type="number" name="quantity" min="1" max="5"></span>';
            $str.='<span>' . $row['pris'] . '</span>';
            $str.='<span><input type="submit" name="action" value="add"></span>';
            $str.="</form>";
            $str.='</div>';
        }
        echo $str;
        ?>
</body>
</html>