"Purchase" button on cart that reduces stock levels

mikebyrne · April 5, 2008

I've setup a working shopping cart but wanted to add a "Purchase" button that would reduce the ammount of items purchased from my field Stocklevel

Cart.php

<?php
// Include MySQL class
require_once('mysql.class.php');
// Include database connection
require_once('global.inc.php');
// Include functions
require_once('functions.inc.php');
// Start the session
session_start();
// Process actions
$cart = $_SESSION['cart'];
$action = $_GET['action'];
switch ($action) {
case 'add':
	if ($cart) {
		$cart .= ','.$_GET['id'];
	} else {
		$cart = $_GET['id'];
	}
	break;
case 'delete':
	if ($cart) {
		$items = explode(',',$cart);
		$newcart = '';
		foreach ($items as $item) {
			if ($_GET['id'] != $item) {
				if ($newcart != '') {
					$newcart .= ','.$item;
				} else {
					$newcart = $item;
				}
			}
		}
		$cart = $newcart;
	}
	break;
case 'update':
if ($cart) {
	$newcart = '';
	foreach ($_POST as $key=>$value) {
		if (stristr($key,'qty')) {
			$id = str_replace('qty','',$key);
			$items = ($newcart != '') ? explode(',',$newcart) : explode(',',$cart);
			$newcart = '';
			foreach ($items as $item) {
				if ($id != $item) {
					if ($newcart != '') {
						$newcart .= ','.$item;
					} else {
						$newcart = $item;
					}
				}
			}
			for ($i=1;$i<=$value;$i++) {
				if ($newcart != '') {
					$newcart .= ','.$id;
				} else {
					$newcart = $id;
				}
			}
		}
	}
}
$cart = $newcart;
break;
}
$_SESSION['cart'] = $cart;
?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>PHP Shopping Cart Demo &#0183; Cart</title>
<link rel="stylesheet" href="styles.css" />
</head>

<body>

<div id="shoppingcart">

<h1>Your Shopping Cart</h1>

<?php
echo writeShoppingCart();
?>

</div>

<div id="contents">

<h1>Please check quantities...</h1>

<?php
echo showCart();
?>

<p><a href="login.php">Back to shop...</a></p>

</div>

</body>
</html>

Functions.php

<?php
function writeShoppingCart() {
$cart = $_SESSION['cart'];
if (!$cart) {
	return '<p>You have no items in your shopping cart</p>';
} else {
	// Parse the cart session variable
	$items = explode(',',$cart);
	$s = (count($items) > 1) ? 's':'';
	return '<p>You have <a href="cart.php">'.count($items).' item'.$s.' in your shopping cart</a></p>';
}
}

function showCart() {
global $db;
$cart = $_SESSION['cart'];
if ($cart) {
	$items = explode(',',$cart);
	$contents = array();
	foreach ($items as $item) {
		$contents[$item] = (isset($contents[$item])) ? $contents[$item] + 1 : 1;
	}
	$output[] = '<form action="cart.php?action=update" method="post" id="cart">';
	$output[] = '<table>';
	foreach ($contents as $id=>$qty) {
		$sql = 'SELECT * FROM product WHERE ProductNo = '.$id;
		$result = $db->query($sql);
		$row = $result->fetch();
		extract($row);
		$output[] = '<tr>';
		$output[] = '<td><a href="cart.php?action=delete&id='.$id.'" class="r">Remove</a></td>';
		$output[] = '<td>'.$ProductName.' by '.$Productinfo.'</td>';
		$output[] = '<td>€'.$Price.'</td>';
		$output[] = '<td><input type="text" name="qty'.$id.'" value="'.$qty.'" size="3" maxlength="3" /></td>';
		$output[] = '<td>€'.($Price * $qty).'</td>';
		$total += $Price * $qty;
		$output[] = '</tr>';
	}
	$output[] = '</table>';
	$output[] = '<p>Grand total: <strong>€'.$total.'</strong></p>';
	$output[] = '<div><button type="submit">Update cart</button></div>';
	$output[] = '</form>';
} else {
	$output[] = '<p>You shopping cart is empty.</p>';
}
return join('',$output);
}
?>

mikebyrne · April 5, 2008

My products table looks like this

CREATE TABLE `product` (

`Producttype` varchar(4) collate latin1_general_ci default NULL,

`ProductName` varchar(80) collate latin1_general_ci default NULL,

`ProductNo` double(50,0) NOT NULL auto_increment,

`Stockamount` decimal(5,0) default NULL,

`Display` varchar(3) collate latin1_general_ci default NULL,

`Description` varchar(1000) collate latin1_general_ci default NULL,

`Price` decimal(6,2) default NULL,

`Image` varchar(50) collate latin1_general_ci default NULL,

`Imgae2` varchar(50) collate latin1_general_ci default NULL,

PRIMARY KEY (`ProductNo`)

) ENGINE=MyISAM AUTO_INCREMENT=17 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci;

mikebyrne · April 5, 2008

I assume I need a piece of sql around the purchase button something like:

UPDATE $table SET stockamount = stockamount - 1 WHERE ProductNo = $id

Just not sure how to code it correctly

GingerRobot · April 8, 2008

What are you struggling with? What exactly is the problem? That query looks fine to me.

mikebyrne · April 8, 2008

The query works its the setting up of the button on the form i cant get right

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"Purchase" button on cart that reduces stock levels

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