将项添加到数组，但如果它们存在于数组中，则增加该值

Question

Today I am working on the shopping cart for a users website script. When they add an item to the cart, it is stored in a $_SESSION variable called cartitems. I am storing arrays within the array of $_SESSION['cartitems'] that contain the item's itemid and the quantity of the items they are trying to add to the cart. Simply adding the items works awesome using the code I list below this, but I need them to increase the value of the items in the array assuming they try and add more of the same item instead of simply adding a new array into the SESSION. Heres an example:

-> User 1 visits the website.
    - Add 5 melons to cart.
    - Add 3 lemons to cart.
    - Add 2 more melons to cart.

My array would print something like:

 array(
        array{0 => 1, 1 => 5},
        array{0 => 2, 1 => 3},
        array{0 => 1, 1 => 2}
 )

.. while the goal of adding them would be something instead like the following:

 array(
        array{0 => 1, 1 => 7},
        array{0 => 2, 1 => 3}
 )

So that the value on the itemid of 1 would be increased to 7. I also need to know what its at, before adding the extra 2, incase there is only 6 melons in stock. Wouldn't want someone finding a way to add more melons then there are left in the stock field now would we!

I am already passing the stock field amount, along with weather it has unlimited stock support, or buy limits on an item, so I have all the information I need to limit stuff (which I already do when adding the items), just need a way to change the array if its already in there to increase the number is all. Here's the code I use to add items:

if(isset($_POST['quantity'])) {
    // Cast quantity to an int for protection
    $quantity = (int) $_POST['quantity'];
    if(!empty($quantity) && $quantity > 0) {
        $errors = 0;
        // It doesn't support unlimited stock so we check stock level
        if($unlimstock == "0") {
            if($quantity > $stock) {
                $quantity = $stock;
            }
            if($buylimit > 0) {
                if($quantity > $buylimit) {
                    $errors = "1";
                }
            }
        }
        if($errors == 0) {
            $_SESSION['cartitems'][] = array($itemid, $quantity);
            header("Location: cart.php");
            die();
        }
    }
}

What is the best approach to check if it's in the array, if it is increase the value, if not I can add it like I am already, and if it is, what is the value so I know how much it can be increased by. Thanks guys!

Answer 1

To simplify code your $_SESSION['cartitems'] should store data as:

$_SESSION['cartitems'] = [
    'product_id1' => 'quantity1',
    'product_id2' => 'quantity2',
];

Then updating a quantity is:

if (isset($_SESSION['cartitems'][$product_id])) {
    $_SESSION['cartitems'][$product_id] += $quantity;
} else {
    $_SESSION['cartitems'][$product_id] = $quantity;
}

If changing $_SESSION['cartitems'] structure is not possible, then you have to iterate over it:

$found = false;
foreach ($_SESSION['cartitems'] as $key => $item) {
    // I suppose that 0-indexed element stores id
    if ($item[0] == $product_id) {
        // I suppose that 1-indexed element stores quantity
        $_SESSION['cartitems'][$key][1] += $quantity;
        $found = true;

        // break as certain element found
        break;
    }
}
if (!$found) {
    $_SESSION['cartitems'][] = array($product_id, $quantity);
}