Adding multiple items to a basket page. PHP Sessions & SQL.

Hi guys,

At the moment I've managed to create a database of art images. I can then get those images from my SQL database and create html code for them to be displayed on a page (arts.php) based on category.

I've added a "purchase" button to them, which, when I click it, adds the item to the shop page (shop.php).

At the moment, I have figured out how to send one single item to the shop page using the following code:

<!-- The purchase button(on every single art item): It contains the GET queries for the item's ID and category.-->

<a href='addtocart.php?cat=".$item["category"]."&id=".$item["ID"]."' class='back-img cart-button purchase-cart' role='button'></a>

After clicking the puchase button, the following code is then executed on addtocart.php

<?php
    session_start();
    if(isset($_GET['id']) & !empty($_GET['id'])){
            $cat = $_GET['cat'];
            $items = $_GET['id'];
            $_SESSION['cart'] = $items;
            header('location: art.php?cat='.$cat.'&status=success');
    }else{
        header('location: art.php?cat='.$cat.'&status=failed');
    }
?>

The user only sees the art.php refresh (although the query changes). However, in the back end, a session variable is created holding the ID of the art item clicked for purchase. This session variable is used on shop.php to create the html for the item.

The only thing is, I want to be able to add several items. I've tried to use the following code:

<?php
    session_start();
    if(isset($_GET['id']) & !empty($_GET['id'])){
            $items = $_GET['id'];
            $cat = $_GET['cat'];
            $_SESSION['cart'] = $items;
            header('location: art.php?cat='.$cat.'&status=success');
    }else{
        header('location: art.php?cat='.$cat.'&status=failed');
    }
    if(isset($_SESSION['cart']) & !empty($_SESSION['cart'])){
        $items = $_SESSION['cart'] . "," . $_GET['id'];
        $cartitems = explode(",", $items);
        $_SESSION['cart'] = $items;
        $_SESSION['cartItems'] = $cartitems;
        header('location: art.php?cat='.$cat.'&status=success');
    }else{
        $items = $_GET['id'];
        $_SESSION['cart'] = $items;
        header('location: art.php?cat='.$cat.'&status=success');
    }
?>

For some reason, though, when I click a different item, it doesn't the new ID to the list (exploding it with a comma), instead it just makes two of the most recent item clicked.

For example. Var_dump of $_SESSION['cart'] using just the single item code: string(1) "5"

var_dump using the multiple item code: string(3) "5,5"

I want it to create an array of the different items I click, so I can foreach loop cycle through the array and recreate all the items purchased to my shop.php page.

Here is the site so you can see what I mean live: https://phlegethontic-flash.000webhostapp.com/art.php

Can anyone give me any tips on what to do?

Thanks,

Parv