Quite possibly one of the most common uses of session cookies is the ability to track items customers intend to purchase while browsing through an online store. Just like old-fashioned shopping carts, the online shopping cart should allow customers to place one or more of an item into the cart, view the cart contents at any time, and remove any item from the cart — all with the benefit of not having to listen to a squeaky cart wheel!
This section shows you how to use session cookies to implement simple shopping carts in your own dynamic web applications.
Removing items from a cart
Because each product in the cart is a separate array element of the session cookie, you can handle each product individually, as long as you know the product name that you used for the array key. To remove an individual product, just specify it in the unset() function:
unset($_SESSION['cart']['apples']);
This statement removes just the apples array key and its value from the array, leaving any other items still in the array. If you want to remove the entire shopping cart, you'd use the following:
session_unset($_SESSION['cart']);
This statement removes the entire cart session cookie. To start a new cart, your code would need to create a new cart session cookie and make it an array variable.
Be careful when unsetting the individual shopping cart items or the entire session cookie, because there’s no going back. When you remove a session cookie, it’s gone and can’t be recovered!
Putting it all together
As you can tell, working with a shopping cart is a multistep process, and it can get somewhat complicated. Let’s take a look at an example of using a shopping cart on a web page. Listing 6-1 shows the code.
LISTING 6-1 The carttest.php Program
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<head>
<title>Shopping Cart Test</title>
</head>
<body>
<h1>Items available</h1>
<form action="carttest.php" method="post">
<table>
<tr><th>Item</th><th>Quantity</th></tr>
<tr><td>Apples</td><td><input type="text" name="apples" size="2"></td></tr>
<tr><td>Bananas</td><td><input type="text" name="bananas" size="2"></td></tr>
</table>
<input type="submit" value="Click to add to cart">
</form>
<br>
<?php
if (isset($_POST['apples'])) {
if (is_numeric($_POST['apples'])) {
$_SESSION['cart']['apples'] = $_POST['apples'];
} elseif ($_POST['apples'] == "Remove") {
unset($_SESSION['cart']['apples']);
}
}
if (isset($_POST['bananas'])) {
if (is_numeric($_POST['bananas'])) {
$_SESSION['cart']['bananas'] = $_POST['bananas'];
} elseif ($_POST['bananas'] == "Remove") {
unset($_SESSION['cart']['bananas']);
}
}
?>
<fieldset style="width:300px">
<legend>Your Shopping Cart</legend>
<?php
if (!isset($_SESSION['cart'])) {
$_SESSION['cart'] = array();
echo "Your shopping cart is empty\n";
} else {
echo "<form action=\"carttest.php\" method=\"post\">\n";
echo "<table>\n";
echo "<tr><th>Item</th><th>Quantity</th><th/></tr>\n";
foreach($_SESSION['cart'] as $key => $value) {
echo "<tr><td>$key</td><td>$value</td>\n";
echo "<td><input type=\"submit\" name=\"$key\" value=\"Remove\"></td></tr>\n";
}
echo "</table>\n";
echo "</form>\n";
}
?>
</fieldset>
</body>
</html>
Listing 6-1 shows the carttest.php program, which I'll walk through to demonstrate using a shopping cart. The first part of the program creates a simple form for selecting the products to purchase. The code lists two products — apples and bananas — and provides a text box to indicate the quantity of each you want to place in the shopping cart.
The next section uses PHP code to check whether the form has already been submitted. If the site visitor has submitted the form, the PHP code checks to see which (if any) of the products had been selected for purchase. If either one had been selected, the PHP code stores the new quantity number in the cart session cookie for that product:
if (isset($_POST['apples'])) {
if (is_numeric($_POST['apples'])) {
$_SESSION['cart']['apples'] = $_POST['apples'];
Next, the code shows the shopping cart status. If there isn’t a shopping cart session cookie, one is created:
$_SESSION['cart'] = array();
If a shopping cart session cookie exists, the program creates a form containing the shopping cart items, along with a Remove button. The foreach statement is used to iterate through each of the items in the shopping cart:
foreach($_SESSION['cart'] as $key => $value) {
echo "<tr><td>$key</td><td>$value</td>\n";
echo "<td><input type=\"submit\" name=\"$key\" value=\"Remove\"></td></tr>\n";
}
Because there are two forms on the web page, you need to add some more code to check if a Remove button has been clicked by the shopper. That was added to the code that checks for the other form data:
} elseif ($_POST['apples'] == "Remove") {
unset($_SESSION['cart']['apples']);
}
Follow these steps to test the carttest.php program:
- Open your editor and enter the code from Listing 6-1.
-
Save the file as carttest.php in the DocumentRoot folder for your web server.
It's important that you use this exact filename because the forms use that as the action attribute.
- Ensure that the Apache web server is running, and then open your browser and enter the following URL:
http://localhost:8080/carttest.php
- Enter a quantity to purchase for one of the items, and then click the Click to Add to Cart button.
- Enter a quantity to purchase for the other item, and then click the Click to Add to Cart button.
- Click the Remove button for one of the items.
- Repeat the process to add or remove products in the shopping cart.
- Close your browser and close the Apache web server when you’re done.
When you first open the carttest.php file, the shopping cart should show that it’s empty, as shown in Figure 6-6.
When you enter a quantity for a product and then click the button to submit it, the product and quantity appear in the shopping cart, as shown in Figure 6-7.
Click the Remove button to remove a product from the shopping cart, or add more quantity of a product to change the value shown in the shopping cart. Congratulations! You’ve just created a simple shopping cart!
Storing data
Most modern browsers allow you to block third-party cookies separate from session or persistent cookies, allowing you to use cookies for normal operations but block third-party cookies trying to track your website history.
