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I'm wondering what is the best way to organize book-page content without involving taxonomies. So for example, I have a math book with a bunch of problems that I wish to list. I have a custom post type qa which can include a taxonomy <book-name>, and I want the URL to be: <domain>/qa/<book-name>/<page-number>/<problem-number>. So creating such a structure isn't a big deal except the <page-number> - there will be lots of pages, and I think that it is not practical to create so many taxonomies. So what will be the optimal implementation? I'd appreciate any suggestions.

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I don't know if this is the optimal, it's one suggestion.

For me I'd created the qa post type as hierachical.

Then for every page in the book I'd created a child qa post using menu_order field to handle the page number.

This child has a 3rd level child for problems.

Hooking intro pre_get_posts for qa archive, you can set the post_parent to 0, so in the archive view you get only books, and not the big list of pages and problems.

Last thing to is create a rewrite rule that convert the url into some query vars.

E.g.

<domain>/qa/<book-name>/<page-number>/<problem-number> should be rewritten in

 <domain>/index.php?name=<book-name>&post_type=qa&number=<page-number>&problem=<problem-number>

That url will end in a very simple query where post id = <problem-number>.

Example code:

function my_book_rules() {
  add_rewrite_rule( 'qa/([^/]+)/([0-9]+)/([0-9]+)$', 'index.php?&post_type=qa&name=$matches[1]&number=$matches[2]&problem=$matches[3]', 'top' );
  add_rewrite_rule( 'qa/([^/]+)/([0-9]+)$', 'index.php?&post_type=qa&name=$matches[1]&number=$matches[2]', 'top');
}
add_action('init', 'my_book_rules');

function my_book_query_vars($vars) {
  $vars[] = 'problem';
  $vars[] = 'number';   
  return $vars;
}

add_filter('query_vars', 'my_book_query_vars'); 

function my_book_query( $query ) {
  if ( is_admin() || ! is_main_query() ) return;
  if ( is_archive() && $query->get('post_type') == 'qa') {
     $query->set('post_parent', 0);
  } elseif ( is_single() && get_post_type() == 'qa') {
    $post = get_queried_object();
    if ( $post->post_parent == 0 && $query->get('number') && ! $query->get('problem') ) {
      // a page number is requested
      $query->set('name', '');
      global $wpdb;
      $n = intval($query->get('number'));
      $p = (int) $wpdb->get_var("SELECT ID FROM $wpdb->posts WHERE post_status = 'publish' AND post_type = 'qa' AND post_parent = $post->ID AND menu_order = $n");
      $query->set('p', $n);
    } elseif( $query->get('problem') ) {
      // a problem is required
      $query->set('name', '');
      $n = intval($query->get('problem'));
      $query->set('p', $n);
    }
  }
}
add_action('pre_get_posts', 'my_book_query');

In the single view template single-qa.php you can load sub tempalte for books, pages or problems, something like:

if ( $post->post_parent == 0 ) {
   get_template_part('book', 'content');
} else {
  $parent = get_post( $post->post_parent );
  if ( $parent->post_parent == 0 ) {
    get_template_part('page-number', 'content');
  } else {
    get_template_part('problem', 'content');
  }
}

Another snippet is for display the book title and the page number inside the problem template (problem-content.php according to previous snippet),

$thepage = get_post( $post->post_parent);
$pagenumber = $thepage->menu_order
$the_book = get_post( $thepage->post_parent )->post_title

echo "The problem " . get_the_title() . 
  " is in the book " . $the_book->post_title .
  " at the page number " . $pagenumber;

Note that the code is a proof of concept and untested.

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  • Thank you sir. I've got the idea. I'm new to WP and I want to ask you what does the $query->set('p', $foo); mean? I've chosen to modify the architecture a bit, introducing new table which will hold data about books. Can I create my own query in my_book_query such that the fetched items will be available at single-qa.php? Because WP supplies methods such as the_title() and the_content() in single.php, but can I affect the way these methods work without hardcoding the core files? Can it be done in the my_book_query method? – somebody Sep 7 '13 at 14:19
  • I'm asking this because I have to execute a certain queries for my new tables in the db (so I don't have to create this nested structure you've suggested). I just want to execute different query for each option: if it is qa/<book-name> then I'll fetch on my own the pages and I would like to pass the result to single-qa.php. If it is qa/<book-name>/<book-page> I would like to execute a different query, fetching all the problems and sending it, again, to single-qa.php. So can I update somehow the object that operates the whole single-qa.php thing? Thanks. – somebody Sep 7 '13 at 14:25
  • I guess I could fetch the book name or book page in single-qa.php using $_SERVER['REQUEST_URI']; and then execute queries for different conditions, but I know that WP has already executed its own queries and there's some data in methods like the_title() and the_content(), so I want to avoid making unnecessary queries. That is why I want to affect the way WP fetches the object that operates single-qa.php. I hope that I explained myself better. Thank you in advance! – somebody Sep 7 '13 at 14:31
  • the_title() and other template tags use global $post variable to work. If you use your custom table to store data, you need extra code to make it works. It's hard to explain here in a comment, expecially without knowing how you have structured your table. The built-in query runned by wordpress known as 'main query', can be edited before it run using 'pre_get_posts' hook. My function does that, and query->set is the way to change the WP main query. If you work with your custom table you have to create your custom query and query->set will be un-useful for you, I think. @somebody – gmazzap Sep 7 '13 at 15:52

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