Substract Session[cart] QUANTITY to STOCK QUANTITY in db - php

Question

I have a table wich show the ($_SESSION['cart'] with a form inside where I can introduce manually the quantity I want into my ($_SESSION['cart'] PRODUCTS.
<form name="formulario2" method="POST" target="oculto"><input type="hidden" name="action" value="update">
foreach($_SESSION['cart'] as $product_id => $quantity) {
echo "<td align=\"center\"><input type = \"text\" size=\"1\" name=\"qty[$product_id]\" value =\"{$_SESSION['cart'][$product_id]}\"></td>";
}
</form>
Then I use the following to update the ($_SESSION['cart']) quantity
<?php
if(isset($_POST['action']) && ($_POST['action'] =='update')){
//
foreach ($_POST['qty'] as $product_id=> $quantity){
$qty = (int)$quantity;
if ($qty > 0){
$_SESSION['cart'][$product_id] = $qty;
}
}
}
?>
Now I would like to SUBSTRACT those quantities I have UPDATED to the ($_SESSION['cart']) to the quantities in STOCK in my data base.
I think that in the last "foreach ($_POST['qty']" I should also say to substract the QUANTITY UPDATED to the DATA BASE QUANTITY but I dont know how to do it. ANY HELP?

Answer 1

1) Replace value =\"{$_SESSION['cart'][$product_id]}\" with value =\"{$quantity}\". You have it already retrieved in the foreach statement.
2) For the database, having that you use mysql, I would reccommend accessing the database with PDO (I have rewritten your second block of code due to its lack of indentation and not matching parentheses):
<?php
if ((isset($_POST['action']) && ($_POST['action'] == 'update'))
{
foreach ($_POST['qty'] as $product_id => $quantity)
{
$qty = intval($quantity);
$pid = intval($product_id); // ALSO use the intval of the $product_id,
// since it was in a form and it can be hacked
$_SESSION['cart'][$pid] = $qty; // NOTE: you need to also update the
// session`s cart with 0 values, or
// at least to unset the respective
// product:
// unset($_SESSION['cart'][$pid])
if ($qty > 0)
{
// now update the DB:
$mysql_host = "127.0.0.1";
$mysql_user = "root";
$mysql_password = "";
$mysql_database = "myShop";
$dbLink = new PDO("mysql:host=$mysql_host;dbname=$mysql_database;charset=utf8", $mysql_user, $mysql_password, array(PDO::ATTR_PERSISTENT => true));
$dbLink->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
$query = $dbLink->prepare("update `products` set `stock` = `stock` - ? WHERE `productId` = ? limit 1");
$query->execute(array($qty, $pid));
}
}
}
?>
Hope it works for you!
Regards!