Shopping Cart Implementation - DWCS Course 2025-26

Introduction

A shopping cart is a core feature of e-commerce applications. This guide demonstrates how to implement a session-based shopping cart using real examples from the DWCS course materials.

Shopping Cart Architecture

System Components

Authentication

User must be logged in to access the cart

Product Listing

Display available products with “Add to Cart” buttons

Session Storage

Store cart items in $_SESSION['cesta']

Cart View

Show items, quantities, and total price

Checkout

Process the order and clear the cart

Session-Based Cart Storage

Cart Data Structure

The shopping cart is stored as an array in the session:

$_SESSION['cesta'] = [
    1 => true,  // Product ID 1 is in cart
    3 => true,  // Product ID 3 is in cart
    7 => true   // Product ID 7 is in cart
];

This implementation uses product IDs as keys with boolean values. You could extend this to store quantities: $_SESSION['cesta'][1] = 2 for 2 units of product 1.

Complete Cart Implementation

Product Listing Page

Display products and allow users to add them to cart:

listado.php

<?php
session_start();
if (!isset($_SESSION['nombre'])) {
    header('Location:login.php');
}

require_once 'conexion.php';

// Handle adding product to cart
if (isset($_POST['comprar'])) {
    $id = $_POST['id'];
    if (!isset($_SESSION['cesta'])) {
        $_SESSION['cesta'] = [];
    }
    $_SESSION['cesta'][$id] = true;
}

// Handle clearing cart
if (isset($_POST['vaciar'])) {
    unset($_SESSION['cesta']);
}

// Get all products
$productos = consultarProductos();
?>

Cart View Page

Full implementation from TEMA-05:

cesta.php

<?php
session_start();
if (!isset($_SESSION['nombre'])) {
    header('Location:login.php');
}

require_once 'conexion.php';

if (isset($_SESSION['cesta'])) {
    foreach ($_SESSION['cesta'] as $k => $v) {
        $producto = consultarProducto($k);
        $listado[$k] = [$producto->nombre, $producto->pvp];
        $producto = null;
    }
    cerrar($conProyecto);
}
?>
<!doctype html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"
          integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.3.1/css/all.css"
          integrity="sha384-mzrmE5qonljUremFsqc01SB46JvROS7bZs3IO2EmfFsd15uHvIt+Y8vEf7N7fWAU" crossorigin="anonymous">
    <title>Tema 4</title>
</head>
<body style="background: gray">
<div class="float float-right d-inline-flex mt-2">
    <i class="fa fa-shopping-cart mr-2 fa-2x"></i>
    <?php
    if (isset($_SESSION['cesta'])) {
        $cantidad = count($_SESSION['cesta']);
        echo "<input type='text' disabled class='form-control mr-2 bg-transparent text-white' value='$cantidad' size='2px'>";
    } else {
        echo "<input type='text' disabled class='form-control mr-2 bg-transparent text-white' value='0' size='2px'>";
    }
    ?>
    <i class="fas fa-user mr-3 fa-2x"></i>
    <input type="text" size='10px' value="<?php echo $_SESSION['nombre']; ?>"
           class="form-control mr-2 bg-transparent text-white" disabled>
    <a href="cerrar.php" class="btn btn-warning mr-2">Salir</a>
</div>
<br>
<h4 class="container text-center mt-4 font-weight-bold">Comprar Productos</h4>
<div class="container mt-3">
    <div class="card text-white bg-success mb-3 m-auto" style="width:40rem">
        <div class="card-body">
            <h5 class="card-title"><i class="fa fa-shopping-cart mr-2"></i>Carrito</h5>
            <?php
            if (!isset($_SESSION['cesta'])) {
                echo "<p class='card-text'>Carrito Vacio</p>";
            } else {
                $total = 0;
                echo "<p class='card-text'>";
                echo "<ul>";
                foreach ($listado as $k => $v) {
                    echo "<li>$v[0], PVP ($v[1]) €.</li>";
                    $total += $v[1];
                }
                echo "</ul></p>";
                echo "<hr style='border:none; height:2px; background-color: white'>";
                echo "<p class='card-text'><b>Total:</b><span class='ml-3'>$total (€)</span></p>";
            }
            ?>
            <a href="listado.php" class="btn btn-primary mr-2">Volver</a>
            <a href="pagar.php" class="btn btn-danger">Pagar</a>
        </div>
    </div>
</div>
</body>
</html>

Object-Oriented Implementation

Using Blade Templates

Modern approach from UNIDAD-05-02 exam sample:

cesta.php

<?php
error_reporting(E_ALL & ~E_DEPRECATED);

session_start();
if (!isset($_SESSION['nombre'])) {
    header('Location:login.php');
}

require '../vendor/autoload.php';

use Clases\Producto;
use Philo\Blade\Blade;

$views = '../views';
$cache = '../cache';
$blade = new Blade($views, $cache);

$total = 0;
$listado = [];
if (isset($_SESSION['cesta'])) {
    foreach ($_SESSION['cesta'] as $k => $v) {
        $producto = (new Producto())->consultarProducto($k);
        $listado[$k] = [$producto->nombre, $producto->pvp];
        $total += $producto->pvp;
        $producto = null;
    }
}

$cantidad = 0;
if (isset($_SESSION['cesta'])) {
    $cantidad = count($_SESSION['cesta']);
}

$titulo = 'Cesta';
$encabezado = 'Comprar Productos';
$usuario = $_SESSION['nombre'];

echo $blade
    ->view()
    ->make('vistaCesta', compact('titulo', 'encabezado', 'usuario', 'listado', 'cantidad', 'total'))
    ->render();

Blade Cart Template

vistaCesta.blade.php

@extends('plantillas.plantilla1')

@section('titulo')
    {{$titulo}}
@endsection

@section('encabezado')
    {{$encabezado}}
@endsection

@section('contenido')
    <div class="container mt-3">
        <div class="card text-white bg-success mb-3 m-auto" style="width:40rem">
            <div class="card-body">
                <h5 class="card-title"><i class="fa fa-shopping-cart mr-2"></i>Carrito</h5>

                @if ( count($listado) == 0 )
                    <p class='card-text'>Carrito Vacio</p>
                @else  
                    <p class='card-text'>
                    <ul>
                    @foreach($listado as $k => $v) 
                        <li>{{$v[0]}}, PVP ({{$v[1]}}) €.</li>
                    @endforeach  
                    </ul></p>
                    <hr style='border:none; height:2px; background-color: white'>
                    <p class='card-text'><b>Total:</b><span class='ml-3'>{{$total}} (€)</span></p>
                @endif
                <a href="listado.php" class="btn btn-primary mr-2">Volver</a>
                <a href="pagar.php" class="btn btn-danger">Pagar</a>
            </div>
        </div>
    </div>
@endsection

Cart Operations

Adding Items to Cart

if (isset($_POST['comprar'])) {
    $id = $_POST['id'];
    if (!isset($_SESSION['cesta'])) {
        $_SESSION['cesta'] = [];
    }
    $_SESSION['cesta'][$id] = true;
}

Displaying Product List with Cart Status

vistaListado.blade.php

@extends('plantillas.plantilla1')

@section('titulo')
    {{$titulo}}
@endsection

@section('encabezado')
    {{$encabezado}}
@endsection

@section('contenido')
    <div class="container mt-3">
        <form class="form-inline" name="vaciar" method="POST" action='{{$action}}'>
            <a href="cesta.php" class="btn btn-success mr-2">Ir a Cesta</a>
            <input type='submit' value='Vaciar Carro' class="btn btn-danger" name="vaciar">
        </form>
        
        <table class="table table-striped table-dark mt-3">
            <thead>
            <tr class="text-center">
                <th scope="col">Añadir</th>
                <th scope="col">Nombre</th>
                <th scope="col">Añadido</th>
            </tr>
            </thead>
            <tbody>
            @foreach($productos as $item) 
                <tr>
                    <th scope='row' class='text-center'>
                        <form action='{{$action}}' method='POST'>
                            <input type='hidden' name='id' value='{{$item->id}}'>
                            <input type='submit' class='btn btn-primary' name='comprar' value='Añadir'>
                        </form>
                    </th>
                    <td>{{$item->nombre}}, Precio: {{$item->pvp}} (€)</td>
                    <td class='text-center'>
                        @if( isset($cesta[$item->id]) ) 
                            <i class='fas fa-check fa-2x'></i>
                        @else
                            <i class='far fa-times-circle fa-2x'></i>
                        @endif
                    <td>
                </tr>
            @endforeach
            </tbody>
        </table>
    </div>
@endsection

Clearing the Cart

if (isset($_POST['vaciar'])) {
    unset($_SESSION['cesta']);
}

Checkout Process

pagar.php

<?php
session_start();
if (!isset($_SESSION['nombre'])) {
    header('Location:login.php');
}
?>
<!doctype html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"
          integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.3.1/css/all.css"
          integrity="sha384-mzrmE5qonljUremFsqc01SB46JvROS7bZs3IO2EmfFsd15uHvIt+Y8vEf7N7fWAU" crossorigin="anonymous">
    <title>Tema 4</title>
</head>
<body style="background: grey">
<div class="float float-right d-inline-flex mt-2">
    <i class="fas fa-user mr-3 fa-2x"></i>
    <input type="text" size='10px' value="<?php echo $_SESSION['nombre']; ?>" class="form-control
    mr-2 bg-transparent text-white" disabled>
    <a href="cerrar.php" class="btn btn-warning mr-2">Salir</a>
</div>
<br>
<h4 class="container text-center mt-4 font-weight-bold">Tienda onLine</h4>
<div class="container">
    <p class="font-weight-bold">Pedido realizado Correctamente.</p>
    <a href="listado.php" class="btn btn-info mt-3">Hacer otra Compra</a>
</div>

</body>
</html>

In a production application, the checkout page should:

Save the order to a database
Process payment
Send confirmation email
Clear the cart only after successful payment
Generate an order number for tracking

Cart Counter Display

Header with Cart Count

<div class="float float-right d-inline-flex mt-2">
    <i class="fa fa-shopping-cart mr-2 fa-2x"></i>
    <?php
    if (isset($_SESSION['cesta'])) {
        $cantidad = count($_SESSION['cesta']);
        echo "<input type='text' disabled class='form-control mr-2 bg-transparent text-white' value='$cantidad' size='2px'>";
    } else {
        echo "<input type='text' disabled class='form-control mr-2 bg-transparent text-white' value='0' size='2px'>";
    }
    ?>
    <i class="fas fa-user mr-3 fa-2x"></i>
    <input type="text" size='10px' value="<?php echo $_SESSION['nombre']; ?>"
           class="form-control mr-2 bg-transparent text-white" disabled>
    <a href="cerrar.php" class="btn btn-warning mr-2">Salir</a>
</div>

Blade Version

<div class="float float-right d-inline-flex mt-2">
    <i class="fa fa-shopping-cart mr-2 fa-2x"></i>
    <input type='text' disabled class='form-control mr-2 bg-transparent text-white' value='{{$cantidad}}' size='2px'>
    <i class="fas fa-user mr-3 fa-2x"></i>
    <input type="text" size='10px' value='{{$usuario}}' class="form-control mr-2 bg-transparent text-white" disabled>
    <a href='cerrar.php' class='btn btn-danger mr-2'>Salir</a>
</div>

Database Integration

Product Class

Producto.php

<?php
namespace Clases;

use PDO;
use PDOException;

class Producto extends Conexion
{
    private $id;
    private $nombre;
    private $pvp;

    public function __construct()
    {
        parent::__construct();
    }

    public function consultarProducto($id)
    {
        $consulta = "SELECT * FROM productos WHERE id = :i";
        $stmt = $this->conexion->prepare($consulta);
        
        try {
            $stmt->execute([':i' => $id]);
        } catch (PDOException $ex) {
            die("Error al consultar producto: " . $ex->getMessage());
        }
        
        return $stmt->fetch(PDO::FETCH_OBJ);
    }

    public function consultarProductos()
    {
        $consulta = "SELECT * FROM productos ORDER BY nombre";
        $stmt = $this->conexion->prepare($consulta);
        
        try {
            $stmt->execute();
        } catch (PDOException $ex) {
            die("Error al consultar productos: " . $ex->getMessage());
        }
        
        return $stmt->fetchAll(PDO::FETCH_OBJ);
    }
}

Enhanced Cart Features

Cart with Quantities

Extend the basic cart to support quantities:

// Add product with quantity
if (isset($_POST['comprar'])) {
    $id = $_POST['id'];
    $cantidad = isset($_POST['cantidad']) ? (int)$_POST['cantidad'] : 1;
    
    if (!isset($_SESSION['cesta'])) {
        $_SESSION['cesta'] = [];
    }
    
    if (isset($_SESSION['cesta'][$id])) {
        $_SESSION['cesta'][$id] += $cantidad;
    } else {
        $_SESSION['cesta'][$id] = $cantidad;
    }
}

// Display cart with quantities
if (isset($_SESSION['cesta'])) {
    $total = 0;
    foreach ($_SESSION['cesta'] as $id => $cantidad) {
        $producto = consultarProducto($id);
        $subtotal = $producto->pvp * $cantidad;
        $total += $subtotal;
        
        echo "<li>";
        echo "$producto->nombre x $cantidad = $subtotal €";
        echo "</li>";
    }
    echo "<p><b>Total: $total €</b></p>";
}

Remove Individual Items

if (isset($_POST['eliminar'])) {
    $id = $_POST['id'];
    unset($_SESSION['cesta'][$id]);
}

Update Quantities

if (isset($_POST['actualizar'])) {
    $id = $_POST['id'];
    $cantidad = (int)$_POST['cantidad'];
    
    if ($cantidad > 0) {
        $_SESSION['cesta'][$id] = $cantidad;
    } else {
        unset($_SESSION['cesta'][$id]);
    }
}

Best Practices

Shopping Cart Security:

Always validate user authentication before cart operations
Validate product IDs exist in database
Sanitize and validate quantities
Never trust prices from client-side; always retrieve from database
Use CSRF tokens for form submissions
Set session timeout for inactive carts
Clear sensitive data after checkout

Complete Workflow

User logs in

Authentication creates session with username

User browses products

Product listing shows available items and cart status

User adds items

Products added to $_SESSION['cesta'] array

User views cart

Retrieve product details from database and calculate total

User proceeds to checkout

Process order and save to database

Clear cart on completion

Remove cart session data after successful order

User logs out

Destroy entire session including cart

Common Patterns

Check if Item is in Cart

if (isset($_SESSION['cesta'][$productId])) {
    echo "✓ In Cart";
} else {
    echo "Add to Cart";
}

Cart Item Count

$itemCount = isset($_SESSION['cesta']) ? count($_SESSION['cesta']) : 0;

Calculate Total

$total = 0;
if (isset($_SESSION['cesta'])) {
    foreach ($_SESSION['cesta'] as $id => $quantity) {
        $producto = consultarProducto($id);
        $total += $producto->pvp * $quantity;
    }
}

Troubleshooting

Cart Not Persisting

Ensure session_start() is called on every page:

<?php
session_start();
// Rest of code

Don’t destroy session during login; only unset specific variables:

// Wrong
session_destroy();

// Right
unset($_SESSION['error']);

Cart Shows Wrong Total

Always retrieve prices from database, not from client:

// Wrong - price from client
$total += $_POST['precio'];

// Right - price from database
$producto = consultarProducto($id);
$total += $producto->pvp;

Summary

A session-based shopping cart provides a simple, effective way to manage user purchases without requiring database storage for each cart operation. By combining sessions for temporary storage with database queries for product information, you can build a robust e-commerce system that maintains cart state throughout the user’s session.

Get Started

PHP Fundamentals

Database Programming

Session Management

Web Services

AJAX & Jaxon

API Integration

Assignments & Exams

​Introduction

​Shopping Cart Architecture

​System Components

​Session-Based Cart Storage

​Cart Data Structure

​Complete Cart Implementation

​Product Listing Page

​Cart View Page

​Object-Oriented Implementation

​Using Blade Templates

​Blade Cart Template

​Cart Operations

​Adding Items to Cart

​Displaying Product List with Cart Status

​Clearing the Cart

​Checkout Process

​Cart Counter Display

​Header with Cart Count

​Blade Version

​Database Integration

​Product Class

​Enhanced Cart Features

​Cart with Quantities

​Remove Individual Items

​Update Quantities

​Best Practices

​Complete Workflow

​Common Patterns

​Check if Item is in Cart

​Cart Item Count

​Calculate Total

​Troubleshooting

​Cart Not Persisting

​Empty Cart After Login

​Cart Shows Wrong Total

​Summary

Build docs developers (and LLMs) love

Introduction

Shopping Cart Architecture

System Components

Session-Based Cart Storage

Cart Data Structure

Complete Cart Implementation

Product Listing Page

Cart View Page

Object-Oriented Implementation

Using Blade Templates

Blade Cart Template

Cart Operations

Adding Items to Cart

Displaying Product List with Cart Status

Clearing the Cart

Checkout Process

Cart Counter Display

Header with Cart Count

Blade Version

Database Integration

Product Class

Enhanced Cart Features

Cart with Quantities

Remove Individual Items

Update Quantities

Best Practices

Complete Workflow

Common Patterns

Check if Item is in Cart

Cart Item Count

Calculate Total

Troubleshooting

Cart Not Persisting

Empty Cart After Login

Cart Shows Wrong Total

Summary