Custom permalink with dynamic rewrite tags on a Wordpress custom post type

Question

I have a custom post type named location and I'm trying to set posts of this type as children of existing pages, to achieve a permalink structure like this:

example.com/alabama  <-- Page with generic content
example.com/alabama/locations  <-- Another page, child of a state page
example.com/alabama/locations/location-name  <- Custom type, child of alabama/locations seen above and titled `Location Name`

The closest I've got to create hierarchical relationships between two distinct post types was through a meta box where I can assign a post ID as the post_parent of my custom type posts when saving them. However despite the page ID being indeed saved to the CPT post_parent field, it has no effect on the permalinks. They are coming as defined in the rewrite CPT option. But I don't know how to make the ['rewrite']['slug'] option dynamic, or if it's even possible.

This is how my post type is being defined:

add_action( 'init', function() {
  register_post_type( 'location', [
    'label' => 'Location',
    'menu_icon' => 'dashicons-location-alt',
    'supports' => [ 'title', 'editor', 'custom-fields' ],
    'public' => true,
    'hierarchical' => false,
    'has_archive' => false,
    'rewrite' => false,
  ] );
} );

How can I configure the rewrite rules for locations to get the permalinks I need?

Answer 1

I'm assuming that all the location posts will have a permalink structure that looks like this:

example.com/{STATE NAME}/locations/{CPT SLUG}

Sample URL addresses:

http://example.com/alabama/locations/location-1
http://example.com/alabama/locations/location-2
http://example.com/new-york/locations/location-3

---

So if that is correct, then:

• Use the add_rewrite_rule() function to add a custom rewrite rule for those permalinks.

• You don't need the /locations/ Page.

add_action( 'init', function(){
    // Handles requests to `your-site-domain.com/{STATE NAME}/locations/{CPT SLUG}`
    add_rewrite_rule(
        '([^/]+)/locations/([^/]+)(?:/([0-9]+))?/?$',
        'index.php?location=$matches[2]&page=$matches[3]&state_name=$matches[1]',
        'top'
    );

    // Allows you to retrieve the `state_name`; for example using `get_query_var()`.
    add_rewrite_tag( '%state_name%', '([\w\-]+)' );
} );

(You can change state_name to another name; it's up to you. And don't forget to flush the rewrite rules — go to the Permalink Settings page and click on the Save Changes button without having to make any changes.)

---

Next, when you create or edit a location post, set the value of the post_parent custom field to the ID of the 'state Page' — eg the /alabama/ Page.

And this code will filter the get_permalink() output, and returns the appropriate permalink for a location post:

add_filter( 'post_type_link', 'so51217355_post_type_link', 10, 2 );
function so51217355_post_type_link( $permalink, $post ) {
    if ( 'location' === $post->post_type ) {
        $page_id = get_post_meta( $post->ID, 'post_parent', true );

        $state_name = ( is_numeric( $page_id ) && $page_id ) ?
            get_post_field( 'post_name', $page_id ) : null;

        // Make sure the post is associated to a valid 'state Page'.
        if ( $state_name ) {
            $permalink = $state_name . '/locations/' . $post->post_name;
            $permalink = home_url( user_trailingslashit( $permalink ) );
        }
    }

    return $permalink;
}

So for example, get_permalink( 123 ) would return http://example.com/alabama/locations/location-1 , if the location post's slug is location-1 , and its 'state Page' is /alabama/ .

---

UPDATE

When the permalink is requested (ie users visit example.com/{STATE NAME}/locations/{CPT SLUG} ), and you want to make sure the 'state Page' and location post both exist, and that the 'state Page' was indeed associated to the location post, then this code can help you:

// Validates the `state_name` of the current page/URL.
add_action( 'parse_request', 'so51217355_parse_request' );
function so51217355_parse_request( $wp ) {
    if ( ! empty( $wp->query_vars['state_name'] ) &&
        ! empty( $wp->query_vars['location'] ) ) {
        global $wpdb;

        $page_id = $wpdb->get_var( $wpdb->prepare(
            "SELECT ID FROM {$wpdb->posts} WHERE post_name = %s",
            $wp->query_vars['state_name']
        ) );

        if ( ! is_numeric( $page_id ) || ! $page_id ) {
            $wp->query_vars['error'] = '404';

            // Don't let WordPress finds a post with nearest match.
            remove_action( 'template_redirect', 'redirect_canonical' );

            return;
        }

        $post_id = $wpdb->get_var( $wpdb->prepare(
            "SELECT ID FROM {$wpdb->posts} WHERE post_name = %s",
            $wp->query_vars['location']
        ) );

        $page_id2 = get_post_meta( $post_id, 'post_parent', true );
        if ( (int) $page_id2 !== (int) $page_id ) {
            $wp->query_vars['error'] = '404';

            // Don't let WordPress finds a post with nearest match.
            remove_action( 'template_redirect', 'redirect_canonical' );
        }
    }
}

UPDATE #2

Refer to the // Comment in the code below this image — see the _so51217355_admin_ajax_js() function.

add_action( 'wp_ajax_so51217355_admin_ajax', '_so51217355_admin_ajax_php' );
function _so51217355_admin_ajax_php() {
    $post_id = filter_input( INPUT_POST, 'post_id' );
    echo get_sample_permalink_html( $post_id );
    wp_die();
}

add_action( 'admin_print_footer_scripts', '_so51217355_admin_ajax_js', 11 );
function _so51217355_admin_ajax_js() {
    $screen = get_current_screen();
    if ( 'location' === $screen->id ) :
    ?>
<script>
// This script will sync the Permalink under the big/main post title box on
// the Edit Post page; but only if and when editing or deleting the custom
// field as in `meta_key` below. Make sure to change it, if necessary.
jQuery( function( $ ){
    var meta_key = 'post_parent';

    function ajax() {
        $.post( ajaxurl, {
            action: 'so51217355_admin_ajax',
            post_id: $( '#post_ID' ).val()
        }, function( s ){
            $( '#edit-slug-box' ).html( s );
        } );
    }

    function _go( e, a ) {
        var $input = $( a.target ),
            mid, mkey;

        if ( /^meta\-(\d+)\-submit$/.test( $input.attr( 'name' ) ) ||
            /^deletemeta\[(\d+)\]$/.test( $input.attr( 'name' ) ) ) {
            mid = RegExp.$1;
            mkey = $( 'input[name="meta[' + mid + '][key]"]' ).val();

            if ( meta_key === mkey ) {
                ajax();
            }
        }
    }

    $( '#the-list' )
        .on( 'wpListAddEnd', _go )
        .on( 'wpListDelEnd', _go );
} );
</script>
    <?php
    endif;
}