Rewrite Wordpress URL to show CPT meta field data

Question

I'm stuck in need of a rewrite rule. I have set up a custom post type for 'Books', each book has a repeatable field (using ACF Pro) for chapters.

I have added a query_var for chapter using the code below...

// Add chapter to query vars array
function add_query_vars_filter( $vars ){
  $vars[] = "chapter";
  return $vars;
}
add_filter( 'query_vars', 'add_query_vars_filter' );

On the single-books.php template page, I have a code to capture the query_var and either display the book overview or the chapter meta fields...

if (get_query_var('chapter') == '') {

    // show book title and content

} elseif (get_query_var('chapter') >= 1) {

    $chapter_no = (get_query_var( 'chapter', 1 ) - 1); //minus one as first array row has index of 0.

    $rows = get_field('chapter'); // get all the rows
    $chapter = $rows[$chapter_no]; // get the row given from query_var

    // show chapter fields from ACF array.
    // $chapter['title']
    // $chapter['content']
    // $chapter['image']

};

So the url for Chapter 1 would look like this...

www.example.com/books/book-title/?chapter=1

This works fine, but for SEO purposes I want the url to look prettier, like the example below...

www.example.com/books/book-title/1/chapter-title/

I've looked at the codex and tried the following...

function custom_rewrite_basic() {
  add_rewrite_rule('^books/([^/]*)/([0-9]+)/?', 'index.php?post_type=books&chapter=$matches[1]', 'top');
}
add_action('init', 'custom_rewrite_basic');

I'm not getting anything from it, not really sure what I need to do/if it's possible. Can anyone point me in the right direction, or show me how to create the rewrite rule.

Thanks.

Answer 1

The post type query var is the same as the post type slug by default. Untested, but this should work-

function custom_rewrite_basic() {
    add_rewrite_rule(
        '^books/([^/]+)/([0-9]+)/([^/]+)/?',
        'index.php?books=$matches[1]&chapter=$matches[2]',
        'top'
    );
}
add_action('init', 'custom_rewrite_basic');

$matches[3] will contain the chapter slug, but if you don't need that to retrieve the chapter, then you don't have to set it.

Rewrite rules need to be flushed after they're added / changed. Visiting the Settings > Permalinks page will flush them without having to call flush_rewrite_rules yourself.

Rewrite rules only handle incoming requests, it's up to you to generate the correct URLs for each chapter, but that should just be a matter of grabbing your chapter data and appending the numbers/titles to the post permalink. Something like this:

$rows = get_field('chapter');
foreach( $rows as $index => $row ){
    echo get_permalink() . '/' . ( $index + 1 ) . '/' . sanitize_title( $row['title'] ) . '/';
}

Also- to keep your templates tidy, you can filter single_template, check if the chapter query var is set, and load a different template for chapters vs the main book page.