Custom query var in wordpress - php

Question

I'm trying to give a pretty url to my custom CPT (Orders). This is the way im trying:
add_filter('post_type_link', 'custom_post_type_link', 1, 3);
function custom_post_type_link( $link, $post = 0 ){
if ( $post->post_type == 'orders' ){
$order_code = 1121000+$post->ID;
return home_url( 'orders/' . $order_code);
} else {
return $link;
}
}
Assume that post ID is 32, This code creates the following url:
http://www.example.com/orders/1121032
Now i wanna write a code to display the post with post ID=32 in above url.
I heard somewhere that i should use custom query vars. But i don't know how to use it.
This is the rest of code i've written
add_filter('query_vars', 'custom_add_query_vars');
function custom_add_query_vars($qVars){
$qVars[] = "code";
return $qVars;
}
add_action( 'init', 'custom_rewrites_init' );
function custom_rewrites_init(){
add_rewrite_rule(
'orders/([0-9]+)?$',
'index.php?post_type=orders&code=$matches[1]',
'top' );
}

Answer 1

After adding custom rewrite rules, wordpress needs to be told to activate the new rule.
Use this method after the add_rewrite_rule function call.
$wp_rewrite->flush_rules();
Warning: flush_rules is expensive, you definitely don't want to call it on every request. Typically you would put the custom_rewrites_init and flush_rules in a plugin register_activation_hook function.
If you're lazy, you can just add it to your code once, make a request to the website (which will rewrite the .htaccess rewrite rules), then comment the flush_rules method out.