Filter By Category Dropdown List With Custom Taxonomies

Question

I have next category dropdown filter that atm supports only two levels "parent -> Child" and I want to get the third "parent -> child -> child".

I have two functions:

function reviews_display_categories_filter( $ancestors = array(), $permalink = '', $parent = 0 ){
    global $reviews_slugs;
    $categories = get_terms( 'review-category', array(
        'hide_empty' => false,
        'parent' => $parent
    ));

    if( !empty( $categories ) ){
        foreach( $categories as $category ){
            $option = '<option value="'.esc_attr( $category->slug ).'" '.( isset( $_GET[$reviews_slugs['review-category']] ) && $_GET[$reviews_slugs['review-category']] == $category->slug ? 'selected="selected"' : '' ).'>';
            $option .= $category->name.' ('.reviews_count_filter( $category ).')';
            $option .= '</option>';
            echo  $option;

            if( in_array( $category->term_id, $ancestors ) ){
                $children = get_term_children( $category->term_id, 'review-category' );
                reviews_display_category_children( $children, $ancestors, $permalink );
            }
        }
    }
}

function reviews_display_category_children( $children, $ancestors, $permalink, $depth = 2 ){
    global $reviews_slugs;
    if( !empty( $children ) ){
        foreach( $children as $child ){
            $term = get_term_by( 'id', $child, 'review-category' );

            $option = '<option value="'.esc_attr( $term->slug ).'" '.( isset( $_GET[$reviews_slugs['review-category']] ) && $_GET[$reviews_slugs['review-category']] == $term->slug ? 'selected="selected"' : '' ).'>';
            $option .= str_repeat('&nbsp;&nbsp;', $depth).$term->name.' ('.reviews_count_filter( $term ).')';
            $option .= '</option>';
            echo  $option;

            if( in_array( $child, $ancestors ) ){
                $children = get_term_children( $child, 'review-category' );
                reviews_display_category_children( $children, $ancestors, $permalink );
            }
        }
    }
}

And it outputs next list:

I want output like this:

Parent
-Child 1
--Child 2

I tried several things, but nothing works at the moment.

Answer 1

Just from skimming your code, it actually pretty much does the same as the WordPress API function wp_dropdown_categories(). It isn't as sophisticated though, no insult intended. Because wp_dropdown_categories() is capable of displaying deeper leveled hierarchies - correctly - then your own function, I can't see a reason for not just using wp_dropdown_categories() for your purpose. If there is a reason, that I have overlooked or just can't see, then you should take a look at the source of wp_dropdown_categories() to get some inspiration and/or guidance from it.