Filter WooCommerce archive pages by an additional category

Question

I'm working on a WooCommerce bookstore site with a custom taxonomy.php template that generates different archive pages based on a category called "Highlights". So, for example, there is a "Best Sellers" archive page that corresponds to /books/product-category/highlights/best-sellers/, producing a list of products assigned to the "Best Sellers" sub-category of "Highlights". On these archive pages, I'd like to include a filter than enables fine-tuning these product lists by a different category called "Topic" (normal WP category, not a custom taxonomy). To get things going, I've been trying to get a $_GET parameter working, such that /highlights/best-sellers/?topic=art would display Best Sellers of that category.

I initially tried using pre_get_posts to no avail, then attempted using the filter woocommerce_product_query_tax_query a described here. The function I've been trying, with various actions/filters is as follows, in functions.php:

function filter_product_topic($query) {

    if( is_admin() ) return;
    if( !$query->is_main_query() ) return;

    $tax_query = $query->get('tax_query');

    if( isset($_GET['topic']) ) {
        $tax_query[] = array(
            'taxonomy'       => 'topic',
            'field'   => 'slug',
            'terms'     => $_GET['topic'],
            'include_children'  => true,
            'operator'   => 'IN'
        );
    }

    $query->set('tax_query', $tax_query);
}

Basically, I ultimately want to selectively invoke this additional query parameter with the filters, to further refine the archive results. So, checking a box for "Art" would refine the archive results in this way. Does anyone know how I might be able to do so? Thank you for any assistance!

Answer 1

you need to add your topic to query_vars.

function so306156_add_query_vars_filter($vars)
{
    $vars[] = "topic";
    return $vars;
}
add_filter('query_vars', 'so306156_add_query_vars_filter');

and then, in pre_get_posts, you check for that var and act accordingly:

function so306156_manipulate_main_query($wp_query)
{
    if (function_exists('is_woocommerce') && !is_admin()) :
        if ($wp_query->is_main_query() && is_woocommerce()) {
            if (isset($wp_query->query_vars['topic'])) {
                $tax_query = $query->get('tax_query');
                $tax_query[] = [
                    'taxonomy' => 'topic',
                    'field' => 'slug',
                    'terms' => $wp_query->query_vars['topic'],
                    'include_children' => true, //true is default so you could leave that one out..
                    'operator' => 'IN' //also default
               ];
            }
        }
    }
}
add_action('pre_get_posts', 'so306156_manipulate_main_query');

im not super sure about the $wp_query->query_vars['topic'] thing in terms, try to echo that one out in the function aka echo <pre>, print_r( $wp_query->query_vars['topic'] ), '</pre>';

and now, i was thinking about another issue.. you created that custom taxonomy topic you are talking about, correct?? because you do not mention that part in your question. in your question you say, that topic is a sub-category of some sort..=?!$%/$%/(???? subcategory of product_cat?? than this stuff above won't work =)