Help Me Understand This Shopping Cart Code Please

[nitediver]

I found these code, but it doesn't have any explanation.

I don't understand the whole concept or like "how it work".

My conclusion is like this:
1.It GET the "id"
2.Select from database
3.It grab the product and put inside "cart session"
4.Put the session inside array

Is that correct?

This is the full code:

<?php
session_start();

$id = $_GET['id'];
$result = mysql_query("SELECT * FROM products WHERE id=$id");
if (!$result) {
    die('Invalid query: ' . mysql_error());
}
$product = mysql_fetch_assoc($result);

if (isset($_SESSION['cart'])) {
    $cart = $_SESSION['cart'];

$in_cart = False;    
foreach ($cart as &$item) {
    if ($item['product']['id'] == $id) {
        $item['quantity'] += 1;
        $in_cart = True;
        break;
    }
}    

if (!$in_cart) {
    $cart[] = array('product' => $product, 'quantity' => 1);
}
} else {
    $cart[] = array('product' => $product, 'quantity' => 1);
}
$_SESSION['cart'] = $cart;

?>

I also have some question :
Why this session appear in if condition without ever declared before?

if (isset($_SESSION['cart'])) {
    $cart = $_SESSION['cart'];

What is "&" mean on "&$item"?

    foreach ($cart as &$item) {
        if ($item['product']['id'] == $id) {
            $item['quantity'] += 1;
            $in_cart = True;
            break;

Why "$cart[] = array('product' => $product, 'quantity' => 1);" appear twice?

    if (!$in_cart) {
        $cart[] = array('product' => $product, 'quantity' => 1);
    }
} else {
    $cart[] = array('product' => $product, 'quantity' => 1);
}
$_SESSION['cart'] = $cart;

[bradgrafelman]

Welcome to PHPBuilder! To answer your questions...

1. nitediver wrote:

   3.It grab the product and put inside "cart session"
   4.Put the session inside array

   Eh.. you've got some terms in the wrong order there. It builds an array ($cart) and then stores that array inside the session. If the array already exists, it adds the product information onto the end of the array and stores the updated array in the session (overwriting the previous array).

2. nitediver wrote:

   Why this session appear in if condition without ever declared before?

   What do you mean it wasn't declared before? For the first product, yes, $SESSION['cart'] won't be set and thus the 'else' statement will be used, which then defines $SESSION['cart']. Thus, on the next page load, $_SESSION['cart'] is defined.

3. nitediver wrote:

   What is "&" mean on "&$item"?

   It's used to indicate a "pass-by-reference" rather than "pass-by-value", meaning rather than handing the foreach() loop a copy of $item, the loop will actually be reading and modifying the $item variable itself.

   If the '&' hadn't been used, the foreach() loop would have been modifying a local copy of the variable, meaning that the actual $item variable would not reflect the changes. See this manual page for more information on references: [man]language.references[/man].

4. nitediver wrote:

   Why "$cart[] = array('product' => $product, 'quantity' => 1);" appear twice?

   Because it needs to be in both places? Follow through the logic of the control structures and you'll see why... that code won't get executed twice on the same page load because of the logic that's being checked.

[nitediver]

Yeah, thanks.

Thank you for explaning.
Now I try to write my own code similar to that one.
But something wrong with, the 2.php only display the last value from array.

1.php,

<?
session_start();

$products = array(
"DC 1" => array("name" => "DC 1", "price" => "35"),
"DC 2" => array("name" => "DC 2", "price" => "26"),
"DC 3" => array("name" => "DC 3", "price" => "31"),
);

foreach($products as &$kart){
echo $kart['name']." - "."$".$kart['price']."<br>";
}
$kart[]= array('name' => $name, 'price' => $price);

$_SESSION['kart'] = $kart;

?>
<hr>
<br><a href="1.php">product</a>
<br><a href="2.php">cart</a>
<br><a href="3.php">clear</a>

Result:
[text]
DC 1 - $35
DC 2 - $26
DC 3 - $31
[/text]

2.php,

<?
session_start();

$kart = $_SESSION['kart'];

foreach($kart as $value){
echo $kart['name']." - "."$".$kart['price']."<br>";
}
$kart[]= array('name' => $name, 'price' => $price);
?>

Result:
[text]
DC 3 - $31
DC 3 - $31
DC 3 - $31
[/text]

I also have another question

"if ($item['product']['id'] == $id) {"

[product] & [id] where that come from, is that an array?

[bradgrafelman]

Your problem is here:

foreach($products as &$kart){ 
echo $kart['name']." - "."$".$kart['price']."<br>"; 
} 
$kart[]= array('name' => $name, 'price' => $price);

You're looping through $products and echo'ing the values as you go, but you don't add anything to $kart until after the loop. I don't see where $name or $price are ever defined, so I'm not even sure what those are supposed to be doing.

I don't think you picked a good example, since you could reduce all of that code down to simply:

$_SESSION['kart'] = $products;

in the first script.

nitediver wrote:

[product] & [id] where that come from, is that an array?

$item is a multi-dimensional, array, yes.

[nitediver]

Ok, thanks I'll try that.

[nitediver]

I still don't understand how this code work, especially the part when the array put inside the session.

Can you give me a list of keyword/tutorial I should search & read, to help me understand this code.