Create additional short URL with custom field and 301 redirect

Question

I want to create an additional shorter Version of my Post-Permalink with a 301 redirect to the real post URL.

The shorter Version of the URL should get its Custom Field I added as a post meta. It is called $trick_nummer

So I have:

mydomain.com/%postname%/

additionally I want:

mydomain.com/Tipp%trick_nummer%

I think it should be something like that:

    add_action("init", "tipp_rewrite_rule");

    function tipp_rewrite_rule() {

        add_rewrite_rule(

            '^tipp([a-zA-Z0-9]+?)',
            'index.php?$trick_nummer%',
            'top'
            );
    }

For example:

mydomain.com/i-am-the-post-name

And the shorter Link (trick_nummer would be '7')

mydomain.com/Tipp7

with a 301 redirect to

mydomain.com/i-am-the-post-name

I found this Question: Redirect short-form URL to long-form URL (post_id to post_id + post_name) But the difference I want is, that I need the number from my custom field.

And I would like to do this in the functions.php

Answer 1

The first step is the rewrite rule. I've also added a rewrite tag so the custom query var will be parsed. You can also use the query_vars filter for this instead.

add_action( 'init', 'tipp_rewrite_rule' );
function tipp_rewrite_rule() {
    add_rewrite_tag( '%trick_nummer%', '([a-zA-Z0-9]+)' );
    add_rewrite_rule(
        '^tipp([a-zA-Z0-9]+)?',
        'index.php?trick_nummer=$matches[1]',
        'top'
    );
}

The second step is to intercept these requests, load the post, and redirect. We use the parse_request action for this, which passes a request object we can check for the presence of the trick_nummer query var.

We then create a new WP_Query to find the post with the matching value in the trick_nummer meta key, and redirect there if one is found:

add_action( 'parse_request', 'wpd_catch_tipp_requests' );
function wpd_catch_tipp_requests( $query ) {
    if( ! is_admin() && isset( $query->query_vars['trick_nummer'] ) ){
        $the_post = new WP_Query(
            array(
                'meta_key'   => 'trick_nummer',
                'meta_value' => $query->query_vars['trick_nummer']
            )
        );
        if( $the_post->have_posts() ){
            wp_redirect( get_permalink( $the_post->post->ID ) );
        } else {
            wp_redirect( home_url() );
        }
    }
}