Add extra parameters after permalink?

How can I add extra parameters after a permalink, specifically if I’m using a custom post type?

For example, let’s say http://mysite/album/record-name was the permalink. How can I make http://mysite/album/record-name/related not turn up a 404 or redirect?

WordPress doesn’t seem to call up the post template if the post doesn’t exist… so I’m at a bit of a loss how to do this.

Answers:

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Method 1

You can add an endpoint to your URIs to handle special requests.

Here is a basic example as plugin. To understand what’s going on read Christopher Davis‘s fantastic tutorial A (Mostly) Complete Guide to the WordPress Rewrite API.

<?php # -*- coding: utf-8 -*-
/**
 * Plugin Name: T5 Endpoint Example
 * Description: Adds a permalink endpoint to posts named <code>epex</code>
 */

add_action( 'init', 't5_add_epex' );

function t5_add_epex()
{
    add_rewrite_endpoint( 'epex', EP_PERMALINK );
}

add_action( 'template_redirect', 't5_render_epex' );

/**
 * Handle calls to the endpoint.
 */
function t5_render_epex()
{
    if ( ! is_singular() or ! get_query_var( 'epex' ) )
    {
        return;
    }

    // You will probably do something more productive.
    $post = get_queried_object();
    print '<pre>' . htmlspecialchars( print_r( $post, TRUE ) ) . '</pre>';
    exit;
}


add_filter( 'request', 't5_set_epex_var' );

/**
 * Make sure that 'get_query_var( 'epex' )' will not return just an empty string if it is set.
 *
 * @param  array $vars
 * @return array
 */
function t5_set_epex_var( $vars )
{
    isset( $vars['epex'] ) and $vars['epex'] = true;
    return $vars;
}

Method 2

You can do this with the Rewrite API‘s add_rewrite_endpoint:

add_action( 'init', 'wpse51444_endpoint' );
function wpse51444_endpoint(){
    add_rewrite_endpoint( 'related', EP_ALL );
}

add_filter( 'query_vars', 'wpse51444_query_vars' );
function wpse51444_query_vars( $query_vars ){
    // add related to the array of recognized query vars
    $query_vars[] = 'related';
    return $query_vars;
}

In the template you can detect when your related query var is present:

if( array_key_exists( 'related' , $wp_query->query_vars ) ):
    // current request ends in related
endif;

Method 3

to add parameter to post url (permalink), i use like this:

add_filter( 'post_type_link', 'append_query_string', 10, 2 );
function append_query_string( $url, $post ) 
{
    return $url.'?my_pid='.$post->ID;
}

output:

http://yoursite.com/pagename?my_pid=12345678

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0