Increase quantity when adding same item to cart session? - php

Question

At the moment, I have a shopping cart that will add an item to the cart session. If another of the same item is added to the cart, it displays duplicate items, each with a quantity of 1.
What do I need to add/change for the code to update the quantity of an existing item? Instead of adding a duplicate item.
add_to_cart.php
session_start();
include 'cart.php';
$item_id = $_POST['item_id'];
$qty = $_POST['qty'];
$counter = $_SESSION['counter'];
$cart = new Cart();
if ($counter>0)
{
$cart = unserialize($_SESSION['cart']);
}
else
{
$_SESSION['counter'] = 0;
$_SESSION['cart'] = "";
}
if (($item_id == "")or ($qty < 1))
{
header("Location: products.php");
}
else
{
require_once('conn_db.php');
$query = "SELECT item_name, price FROM products WHERE (item_id=$item_id)";
$result = mysql_query($query) or die("Database Error");
if(mysql_num_rows($result) == 1)
{
$price = mysql_result($result, 0,"price");
$item_name = mysql_result($result, 0, "item_name");
$new_item = new Item($item_id, $item_name, $qty, $price);
$cart->add_item($new_item);
$_SESSION['counter'] = $counter+1;
$_SESSION['cart'] = serialize($cart);
header("Location: products.php");
mysql_close();
}
else
{
header("Location: products.php");
}
}
cart.php
class Item {
var $item_id;
var $item_name;
var $qty;
var $price;
var $deleted = false;
function get_item_cost() {
return $this->qty * $this->price;
}
function delete_item() {
$this->deleted = true;
}
function Item($item_id, $item_name, $qty, $price) {
$this->item_id = $item_id;
$this->item_name = $item_name;
$this->qty = $qty;
$this->price = $price;
}
function get_item_id() {
return $this->item_id;
}
function get_item_name() {
return $this->item_name;
}
function get_qty() {
return $this->qty;
}
function get_price() {
return $this->price;
}
}
class Cart {
var $items;
var $depth;
function Cart() {
$this->items = array();
$this->depth = 0;
}
function add_item($item) {
$this->items[$this->depth] = $item;
$this->depth++;
}
function delete_item($item_no) {
$this->items[$item_no]->delete_item();
}
function get_depth() {
return $this->depth;
}
function get_item($item_no) {
return $this->items[$item_no];
}
}

Answer 1

Fairly quick example, should put in you in the right direction. You'll need to chance your add_item() to check to see if the cart already contains the item
function add_item($item) {
$item_already_exists = false;
foreach ($this->items as $depth_id => $item_in_cart) { // loop through the current contents of the cart
if ($item_in_cart->get_item_id() == $item->get_item_id()) { // if the item already exists in the cart
$item_already_exists = true;
$item_exists_at = $depth_id;
break;
}
}
if ($item_already_exists == true) { //update the existing item
$this->items[$item_exists_at]->update_qty($item->get_qty());
} else { // add the new item
$this->items[$this->depth] = $item;
$this->depth++;
}
}
Then you'll need to create an update_quantity() in your Item class
function update_qty($qty) {
$this->qty += $qty;
}

Answer 2

Before adding the item check if it already exists in the shopping cart. If False, add it. If True, just change the quantity! :)