Shopping cart using PHP $_Session

Question

I'm learning PHP and I'm trying to create a shopping cart using only PHP and $_SESSION

What I'm trying to achieve is:

Adding an existing product only updates a quantity variable
A delete button that decreases a quantity variable and then removes the item from the cart when quantity = 0
A clear cart button which removes everything from the cart

My current problems are:

Products can be added multiple times but the item keeps reappearing in the cart and the quantity isn't updated.
Neither the delete button nor clear cart button is currently working.

I'm struggling with implementing a global quantity variable, I don't understand how to manage it and update it.

I feel like I'm being a bit hopeful/naive with my delete function and that the array check is off, but I'm unsure how to fix it.

I think that the reset cart function is close, but I'm short one step. I just don't know where

Any help would be or a nudge in the right direction would be appreciated, thanks in advance.

My code

<?php
session_start ();

$items = [
[ "name" => "Lord of the Rings", "price" => 16.72 ],
[ "name" => "The Name of The Wind", "price" => 35.54 ],
[ "name" => "The Way of Kings", "price" => 32.237 ],
[ "name" => "Gravity Rising", "price" => 24.75 ],
[ "name" => "The Hobbit", "price" => 30.30 ],
]; 

//loads cart
if (! isset ( $_SESSION ['cart'] )) {
    $_SESSION ['cart'] = array ();
    
       //Attempt to add quantity variabke for cart
       // for ($i = 0; $i < count($products); $i++) {
       // $_SESSION["qty"][$i] = 0;
       //}
}

// Add
if (isset ( $_POST ["buy"] )) {
     
    //Atempt to add quantity variable 
    //If item is already in cart, quantity += 1. Else add item.
    //if (in_array($_POST ["buy"], $_SESSION['cart'])) {
       $_SESSION ['cart'][] = $_POST["buy"];
       
        
    //}
}

// Delete Item
else if (isset ( $_POST ['delete'] )) { 
    if (false !== $key = array_search($_POST['delete'], $_SESSION['cart'])) { // check item in array
    unset($_SESSION['cart'][$key]); // remove item
    }


    
}

// Empty Cart
else if (isset ( $_POST ["reset"] )) { // remove item from cart
    unset ( $_SESSION ['cart'] );
}

?>

<form action='<?php echo $_SERVER['PHP_SELF']; ?>' method='post'>
  <form action='<?php echo $_SERVER['PHP_SELF']; ?>' method='post'>
    <?php
        foreach ( $items as $ino => $item ) {
            $name = $item ['name'];

            $price = $item ['price'];

            echo " <p>$name</p>";
            echo '<p>$' . number_format((float)$item['price'], 2, '.', '') . '</p>';

            
            echo "<button type='submit' name='buy' value='$ino'>Buy</button> ";
        }

            
        
    ?>
</form>


<?php
if (isset ( $_SESSION ["cart"] )) {
    ?>

<form action='(omitted link)'
target='_blank' method='post'
enctype='application/x-www-form-urlencoded'>
<table>
    <tr>
        <th>Product</th>
        <th>Price</th>
        <th>Quantity</th>
        <th>Action</th>
    </tr>
   <?php
// Set a default total
$total = 0;
foreach ( $_SESSION['cart'] as $ino ) {
    ?>
<tr>
    <td>
        <?php echo $items[$ino]['name']; ?>
    </td>
    <td>
        <?php echo  number_format((float)$items[$ino]['price'], 2, '.', ''); ?>
    </td>
    <td>
        Quantity: <?php echo "";?>        
    </td>
    <td>
        <button type='submit' name='reset' value='<?php echo $ino;    ?>'>Delete</button>
    </td>
</tr>
<?php
    $total += number_format((float)$items[$ino]['price'], 2, '.', '');
} // end foreach
?>

Total: $<?php echo $total; ?>
    <tr>
        <td colspan="2">Total: $<?php echo($total); ?></td>
        
    </tr>
    <tr>
        <td><button type='submit' name='clear'>Clear cart</button></td>
    </tr>
</table>
</form>
<?php  } ?>

SaschaM78 SaschaM78 · Accepted Answer · 2020-07-15T10:47:46

Welcome to Stack Overflow!

There is one major issue with your code:

foreach loop and assignment:

foreach ( $items as $ino => $item ) { in combination with echo "<button type='submit' name='buy' value='$ino'>Buy</button> "; is dangerous. $ino refers to the array index, in the moment a new product is added somewhere in the list (and not at the end of it) all elements in the cart might point to the wrong product.

Example:

You have an array with ['Apple', 'Orange', 'Banana']. User decides to add all three to the cart. The cart now contains [0, 1, 2] or "Apple, Orange, Banana".

If these values would now come from a database, someone might have added "Strawberry" to the list and reordered the catalog so the new array would be something like ['Apple', 'Strawberry', 'Orange', 'Banana']. The cart would still have the old values [0, 1, 2] and would now point to "Apple, Strawberry, Orange". Instead use a product ID right from the start.

Fix and a bit of help:

I am not going to write your code as you want to learn it yourself. But just to give you some advice and help here are some hints.

Use a product ID:

$items = [
[ "pid" => "LOTR", "name" => "Lord of the Rings", "price" => 16.72 ],
[ "pid" => "NameWind", "name" => "The Name of The Wind", "price" => 35.54 ],
[ "pid" => "WayKings", "name" => "The Way of Kings", "price" => 32.237 ],
[ "pid" => "GravRi", "name" => "Gravity Rising", "price" => 24.75 ],
[ "pid" => "Hobbit", "name" => "The Hobbit", "price" => 30.30 ],
];

Use the key in the cart session variable:

In the loop use the ID as product reference:

$pid = $item ['pid'];
echo "<button type='submit' name='buy' value='$pid'>Buy</button> ";

... and increment the value by one if it is already in the cart ...

if (isset ( $_POST["buy"] )) {
    if (array_key_exists($_POST["buy"], $_SESSION['cart'])) {
      $_SESSION['cart'][$_POST["buy"]] += 1;
    } else {
      $_SESSION['cart'][$_POST["buy"]] = 1;
    }
}

Then decrement the value using the same approach for the delete button.

Resetting the cart:

The cart won't get cleared as you are checking for $_POST["reset"] but the button has the name "clear": <button type='submit' name='clear'>Clear cart</button>.

Shopping cart using PHP $_Session

1 Answers