Show Out of stock products at the end in Woocommerce

Is it possible to show out of stock products at the end of a category or page in wordpress?

So the customer first see the products that are available and after that the products that are out of stock.

Answer

This is the same as Viktor & Bogdan’s answer, but without the extra Class code.

It uses the post_clause filter to modify the product query. We JOIN the wp_postmeta table to the query and prepend an orderby _stock_status clause to the existing query. This way any other orderby clauses remain in the query as well.

add_filter('posts_clauses', 'order_by_stock_status');
function order_by_stock_status($posts_clauses) {
    global $wpdb;
    // only change query on WooCommerce loops
    if (is_woocommerce() && (is_shop() || is_product_category() || is_product_tag() || is_product_taxonomy())) {
        $posts_clauses['join'] .= " INNER JOIN $wpdb->postmeta istockstatus ON ($wpdb->posts.ID = istockstatus.post_id) ";
        $posts_clauses['orderby'] = " istockstatus.meta_value ASC, " . $posts_clauses['orderby'];
        $posts_clauses['where'] = " AND istockstatus.meta_key = '_stock_status' AND istockstatus.meta_value <> '' " . $posts_clauses['where'];
    }
    return $posts_clauses;
}

You could change istockstatus.meta_value ASC to istockstatus.meta_value DESC if you for some reason wanted the Out Of Stock items first.

Tested on WP: 4.8; WC 3.0.8