Organizing a PHP page with a bunch of $_POST's - php

Question

I am making quite a large online points/purchasing system in PHP and just have a fundamental question.
All the relevant stuff is on a single PHP page within the site, with "includes" from other parts of the site such as shopping cart, points review, products etc..., but throughout the page there are stages where the user clicks a form submit button to pass values via $_POST.
As there is a main page for all this stuff, I have a part at the top of the page where it takes all the POST values and makes decisions based upon them, like so:
if($_POST['add']) {
$product_id = $_POST['add'];
}
if($_POST['remove']) {
$rid = $_POST['id'];
$cart->del_item($rid);
}
if($_POST['empty']){
$cart->empty_cart();
}
if($_POST['purchase']) {
foreach($cart->get_contents() as $item) {
$sql="INSERT INTO wp_scloyalty_orders VALUES (".$user_id.", ".$item['id'].")";
$result=mysql_query($sql);
}
$cart->empty_cart();
unset($_SESSION['cart']);
}
if($_POST['add']) {
query_posts('post_type=prizes&showposts=-1&p='.$product_id.'');
while (have_posts()) : the_post();
$my_meta = get_post_meta($post->ID,'_my_meta',TRUE);
if($calctotalnew > $my_meta['pointsvalue']){
$cart->add_item(get_the_id(), 1, $my_meta['pointsvalue'], get_the_title());
} else {
echo 'You do not have sufficient points to redeem this product...';
}
endwhile;
wp_reset_query();
}
So my question is... is this really a good way to organize a system, having the form actions go to the same page that the form is on, and have a load of IF statements to decide what to do with the POST values?
Thanks! :)

Answer 1

it's generally best to capture separate POST calls (grouped by type) in separate actions. I usually go as follows:
page 1 has a form, which will submit to eg. product.php?action=add. In product.php you can route the 'add' action to the function add_product() (or whatever). Then when the product is added, just header the user back to the main page (or whatever page you'd like). This immediately tackles the problem with refresh-posts (user refreshing the page which will send the same data again).
following mvc imagine you have a controller Product which handles all the product actions. The skeleton could look like this (assuming function action_x will be executed when yoursite.com/product/x is requested):
class Product_Controller {
function action_show() {
}
function action_update() {
}
function action_delete() {
}
}
if your framework supports a default action of some sort you could route your actions:
function action_default() {
if(method_exists(array($this, 'action_'. $_POST['action']))) {
return call_user_method('action_'. $_POST['action'], $this);
}
}
ofcourse the same can be achieved without controller classes;
if(function_exists('action_'. $_POST['action'])) {
call_user_func('action_'. $_POST['action']);
}
function action_show() { }
...
and to illustrate the discussion in the comments;
function action_update() {
// do some update logic, query an UPDATE to mysql etc.
if($result) {
// optionally save a success message
Message::add('Your record has been updated');
header('Location: main_page.php'); // or another intelligent redirect function
} else {
Message::add('Sorry, something went wrong');
header('Location: error_page.php'); // or also main_page
}
}
This will also keep your code cleaner, as updating/adding/deleting stuff is radically different from showing stuff, this will prevent you from mixing up stuff. You could even call the show function from within the update function if you want to skip the redirect.
But in the end it's a matter of choice, led by pragmatism or your framework ;)
I hope this'll explain everything a bit, don't hesitate to ask for clarification

Answer 2

if you want to separate the logic from the interface then you can simple create new file and put the all logical and database related code in that file and include OR require that file in the view file
like
view.php interface file and
logic.php is your logic file then
first line in view.php is
require_once(logic.php');
and all the logic is in this files
simple MVC

Answer 3

Well, it seems I have to explain.
It absolutely does not matter how much IF statements you have in the POST handler. Your current design is okay, and there is no reason to ask nor change it.
The only thing that you may wish to add to your design is a front controller, which will take both entity (cart) and action("add") and call add() method of $cart class. these methods you may store one under another in the class source.
Though it is quite huge improvement, requiring great rethinking of the whole site architecture. So, you may stick with your current one.
As for your other question, how to display errors, here is an answer: php redirection not working