Wordpress - Custom Post type & Taxonomy URL structure

After forever, I figured out an answer!

First: we register the custom post type & custom taxonomy:

add_action( 'init', 'register_sps_products_post_type' );
function register_sps_products_post_type() {
    register_post_type( 'sps-product',
        array(
            'labels' => array(
                'name' => 'Products',
                'menu_name' => 'Product Manager',
                'singular_name' => 'Product',
                'all_items' => 'All Products'
            ),
            'public' => true,
            'publicly_queryable' => true,
            'show_ui' => true,
            'show_in_menu' => true,
            'show_in_nav_menus' => true,
            'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'comments', 'post-formats', 'revisions' ),
            'hierarchical' => false,
            'has_archive' => 'products',
            'taxonomies' => array('product-category'),
            'rewrite' => array( 'slug' => 'products/%product_category%', 'hierarchical' => true, 'with_front' => false )
        )
    );
    register_taxonomy( 'product-category', array( 'sps-product' ),
        array(
            'labels' => array(
                'name' => 'Product Categories',
                'menu_name' => 'Product Categories',
                'singular_name' => 'Product Category',
                'all_items' => 'All Categories'
            ),
            'public' => true,
            'hierarchical' => true,
            'show_ui' => true,
            'rewrite' => array( 'slug' => 'products', 'hierarchical' => true, 'with_front' => false ),
        )
    );
}

Next, we add a new rewrite rule so Wordpress knows how to interpret our new permalink structure:

add_action( 'generate_rewrite_rules', 'register_product_rewrite_rules' );
function register_product_rewrite_rules( $wp_rewrite ) {
    $new_rules = array( 
        'products/([^/]+)/?$' => 'index.php?product-category=' . $wp_rewrite->preg_index( 1 ), // 'products/any-character/'
        'products/([^/]+)/([^/]+)/?$' => 'index.php?post_type=sps-product&product-category=' . $wp_rewrite->preg_index( 1 ) . '&sps-product=' . $wp_rewrite->preg_index( 2 ), // 'products/any-character/post-slug/'
        'products/([^/]+)/([^/]+)/page/(\d{1,})/?$' => 'index.php?post_type=sps-product&product-category=' . $wp_rewrite->preg_index( 1 ) . '&paged=' . $wp_rewrite->preg_index( 3 ), // match paginated results for a sub-category archive
        'products/([^/]+)/([^/]+)/([^/]+)/?$' => 'index.php?post_type=sps-product&product-category=' . $wp_rewrite->preg_index( 2 ) . '&sps-product=' . $wp_rewrite->preg_index( 3 ), // 'products/any-character/sub-category/post-slug/'
        'products/([^/]+)/([^/]+)/([^/]+)/([^/]+)/?$' => 'index.php?post_type=sps-product&product-category=' . $wp_rewrite->preg_index( 3 ) . '&sps-product=' . $wp_rewrite->preg_index( 4 ), // 'products/any-character/sub-category/sub-sub-category/post-slug/'
    );
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}

The next function on the other hand fixes the issue with the sub-categories. The issue itself consists in the fact, that when you try to load a page with URL faq/category/child-category/, WordPress would try to load a post with slug “child-category” instead of the sub-category with slug “child-category”.

// A hacky way of adding support for flexible custom permalinks
// There is one case in which the rewrite rules from register_kb_rewrite_rules() fail:
// When you visit the archive page for a child section(for example: http://example.com/faq/category/child-category)
// The deal is that in this situation, the URL is parsed as a Knowledgebase post with slug "child-category" from the "category" section
function fix_product_subcategory_query($query) {
    if ( isset( $query['post_type'] ) && 'sps-product' == $query['post_type'] ) {
        if ( isset( $query['sps-product'] ) && $query['sps-product'] && isset( $query['product-category'] ) && $query['product-category'] ) {
            $query_old = $query;
            // Check if this is a paginated result(like search results)
            if ( 'page' == $query['product-category'] ) {
                $query['paged'] = $query['name'];
                unset( $query['product-category'], $query['name'], $query['sps-product'] );
            }
            // Make it easier on the DB
            $query['fields'] = 'ids';
            $query['posts_per_page'] = 1;
            // See if we have results or not
            $_query = new WP_Query( $query );
            if ( ! $_query->posts ) {
                $query = array( 'product-category' => $query['sps-product'] );
                if ( isset( $query_old['product-category'] ) && 'page' == $query_old['product-category'] ) {
                    $query['paged'] = $query_old['name'];
                }
            }
        }
    }
    return $query;
}
add_filter( 'request', 'fix_product_subcategory_query', 10 );

This function lets WordPress know how to handle %product_category% in your custom post type rewrite slug structure:

function filter_post_type_link($link, $post)
{
    if ($post->post_type != 'sps-product')
        return $link;

    if ($cats = get_the_terms($post->ID, 'product-category'))
    {
        $link = str_replace('%product_category%', get_taxonomy_parents(array_pop($cats)->term_id, 'product-category', false, '/', true), $link); // see custom function defined below\
        $link = str_replace('//', '/', $link);
        $link = str_replace('http:/', 'http://', $link);
    }
    return $link;
}
add_filter('post_type_link', 'filter_post_type_link', 10, 2);

A custom function based off of get_category_parents. It gets the taxonomy's parents:

// my own function to do what get_category_parents does for other taxonomies
function get_taxonomy_parents($id, $taxonomy, $link = false, $separator = '/', $nicename = false, $visited = array()) {    
    $chain = '';   
    $parent = &get_term($id, $taxonomy);

    if (is_wp_error($parent)) {
        return $parent;
    }

    if ($nicename)    
        $name = $parent -> slug;        
else    
        $name = $parent -> name;

    if ($parent -> parent && ($parent -> parent != $parent -> term_id) && !in_array($parent -> parent, $visited)) {    
        $visited[] = $parent -> parent;    
        $chain .= get_taxonomy_parents($parent -> parent, $taxonomy, $link, $separator, $nicename, $visited);

    }

    if ($link) {
        // nothing, can't get this working :(
    } else    
        $chain .= $name . $separator;    
    return $chain;    
}

Sources:

• Add Taxonomy in Custom Permalink Structure
• Custom Permalinks Hierarchical Taxonomies