Substract Session[cart] QUANTITY to STOCK QUANTITY in db

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!