Creating customized php files in theme folder

Question

I am developing a e-commerce theme that requires an order page. I created a php file inside my theme folder named order-page.php and hope to access this page from the wordpress root url (example.com/order-page)

add_action('template_redirect', 'template_redirect');
function template_redirect(){
    $basename = basename($_SERVER['QUERY_STRING']);
    echo $basename;
    if($basename=='order-page'){
        loadCustomTemplate(TEMPLATEPATH."/$basename.php");
    }
}

function loadCustomTemplate($template) {
    global $wp_query;
    if(!file_exists($template)){
        return;
    }
    $wp_query->is_page = true;
    $wp_query->is_single = false;
    $wp_query->is_home = false;
    $wp_query->comments = false;
    // if we have a 404 status
    if ($wp_query->is_404) {
    // set status of 404 to false
        unset($wp_query->query["error"]);
        $wp_query->query_vars["error"]="";
        $wp_query->is_404=false;
    }
    // change the header to 200 OK
    //header("HTTP/1.1 200 OK");
    //load our template
    include($template);
    exit;
}

Problem#1: with the function listed above, I can only use example.com/?order-page to get what I want. If I use example.com/order-page, I will get url not found error.

Problem#2: when I have multiple parameters, this function doesn't work anymore. For example, if I have:

example.com/?order-page&product_id=001&type=digital

$basenamewill return order-page&product_id=001&type=digital

Using $query_array=explode('&',$basename) and get $query_array[0] is one possible solution. Is there a better way to do this?

Answer 1

Problem#1:

You can create a customized php file for your page using a Page Template

Page Templates

WordPress looks for template files in the following order:

1. Page Template — If the page has a custom template assigned, WordPress looks for that file and, if found, uses it.
2. page-{slug}.php — If no custom template has been assigned, WordPress looks for and uses a specialized template that contains the page’s slug.
3. page-{id}.php — If a specialized template that includes the page’s slug is not found, WordPress looks for and uses a specialized template named with the page’s ID.
4. page.php — If a specialized template that includes the page’s ID is not found, WordPress looks for and uses the theme’s default page template.
5. index.php — If no specific page templates are assigned or found, WordPress defaults back to using the theme’s index file to render pages.

In your scenario, your page template file would be page-order-page.php, wordpress would then load that file for when someone accesses (example.com/order-page).

Problem#2:

For problem 2, you would need to register query variables using the query_vars filter.

function wpse169050_register_query_vars( $vars ) {
    $vars[] = 'product_id';
    $vars[] = 'type';
    return $vars;
} 
add_filter( 'query_vars', 'wpse169050_register_query_vars' );

Your order url with the variables would then be

example.com/order-page/?product_id=001&type=digital

You can then get the value for both variables using get_query_var in your template file:

$product_id = get_query_var('product_id');
$type       = get_query_var('type');

Answer 2

You should take a look at the WordPress hierarchy page in the documentation. Here it's the relevant part:

page-{slug}.php 

If the page slug is recent-news, WordPress will look to use:

page-recent-news.php

http://codex.wordpress.org/Template_Hierarchy