Add a permalink variable onto custom post type URL after post name slug

Question

I have a custom post type mycpt and I'm trying to allow for a variable to be appended onto the end of the URL right after the post name slug, like this:

www.site.com/mycpt/the-name-of-my-post/var-value-here/

I've been searching around, and the only examples I can find don't use the post name/slug in the URL, but rather taxonomies, so I'm not sure what the correct way to do it is. Here is what I'm trying now, but it's treating the URL with the variable as a separate page type (it's loading a default template rather than the template my custom post type uses).

add_action( 'init', function() {
    add_rewrite_tag( '%my_var%', '([^/]*)' );
    add_rewrite_rule( '^mycpt/(.*)/([^/]*)/?', 'index.php?post_type=mycpt&my_var=$matches[1]', 'top' );
}, 10, 0 );

I also tried changing $matches[1] to $matches[2] since I thought maybe the wildcard for the post name/slug was the first match, but that didn't work either.

Can anybody see what I'm doing wrong here?

Answer 1

Here's a complete working example that adds a post type, with extra rule to capture an additional parameter:

function wpd_post_type_and_rule() {
    register_post_type( 'mycpt',
        array(
            'labels' => array(
                'name' => __( 'mycpt' ),
            ),
            'public' => true,
            'rewrite' => array( 'slug' => 'mycpt' ),
        )
    );
    add_rewrite_tag( '%mycpt_var%', '([^/]*)' );
    add_rewrite_rule(
        '^mycpt/([^/]*)/([^/]*)/?$',
        'index.php?mycpt=$matches[1]&mycpt_var=$matches[2]',
        'top'
    );
}
add_action( 'init', 'wpd_post_type_and_rule' );

After adding this and flushing rewrite rules, you'll have both

www.site.com/mycpt/the-name-of-my-post/

and

www.site.com/mycpt/the-name-of-my-post/var-value-here/

You can get the value of mycpt_var in the template with:

echo get_query_var( 'mycpt_var' );

Answer 2

As a temporary solution you can try using free plugin : https://wordpress.org/plugins/custom-post-type-permalinks/