How to add class to specific navbar item when post parent category is in specific category

Question

I have website with pages which are named the same as categories. For example I have page called Cities and also I have category called Cities. I want to add class to navbar item when user is reading post from specific category. So when I'm reading post from category Cities I want to highlight link in my navbar which going to page Cities. I made simple function

add_filter('nav_menu_css_class' , 'my_nav_special_class' , 10 , 2);
  function my_nav_special_class($classes, $item){

    global $post;

    $category   = get_the_category();

    $slug = $category[0]->slug;
    $slug = str_replace('-', '', strtolower($slug));

    $menu_item = sanitize_title( $item->title );
    $menu_item = str_replace('-', '', strtolower($menu_item));

    if( is_single() && $slug === $menu_item) {
      $classes[] = 'current_page_item';
    }

   return $classes;
}

When the post category match navbar item I'm adding css class. The problem is when post category is for example Tiger and in navbar I have page called Animals. In this case I want to highlight navbar item too. My question is - how can I do this? How the condition should look like when I want to add css class to specific menu item when post have specific cat or cat parent?

Answer 1

It seems like you should use hierarchies of categories, because it sounds like 'Tiger' belongs to the group 'Animals'.

You can get the parent category with $category->parent so if page category was Tiger, and parent category was Animals, this would then work.

Let me know if that would work for you and if you need more info