php - WordPress Next Parent Page Link -

this self q&a.

often in wordpress use page hierarchy build out project structure. example, when doing portfolio sites, common:

• work
  • bmw
    • models
      • 3-series
      • 5-series
  • audi
    • models
      • a3
      • a4

so, when user on 3-series page, you'd have link "next car manufacturer". how can without plugin?

these functions allow set depth want use determine next page. in question, user on '3-series', depth 2. so, link returned "audi" page.

it's used in template (my example using image link text):

$nextimg = '<img src="'.get_template_directory_uri().'/images/icon-nav-right.png"/>';             echo next_project_link($nextimg);  

and place in functions.php:

 /*  * next project link  */     function next_project_link($html) {         global $post;          // change set depth want next page of         $parent_depth = 2;          $ancestors = get_post_ancestors($post);              $current_project_id = $ancestors[$parent_depth-1];          // check cached $pages         $pages = get_transient( 'all_pages' );         if ( empty( $transient ) ){             $args = array(                 'post_type'         => 'page',                 'order'             => 'asc',                 'orderby'           => 'menu_order',                 'post_parent'       => $ancestors[$parent_depth],                 'fields'            => 'ids',                 'posts_per_page'    => -1             );             $pages = get_posts($args);                set_transient('all_pages', $pages, 10 );         }                 $current_key = array_search($current_project_id, $pages);         $next_page_id = $pages[$current_key+1];          if( isset($next_page_id) ) {             // next page exists             return '<a class="next-project" href="'.get_permalink($next_page_id).'">'.$html.'</a>';         }      }    /*  * previous project link  */     function previous_project_link($html) {         global $post;          // change set depth want next page of         $parent_depth = 2;          $ancestors = get_post_ancestors($post);         $current_project_id = $ancestors[$parent_depth-1];          // check cached $pages         $pages = get_transient( 'all_pages' );         if ( empty( $transient ) ){             $args = array(                 'post_type'         => 'page',                 'order'             => 'asc',                 'orderby'           => 'menu_order',                 'post_parent'       => $ancestors[$parent_depth],                 'fields'            => 'ids',                 'posts_per_page'    => -1             );             $pages = get_posts($args);                set_transient('all_pages', $pages, 10 );         }                 $current_key = array_search($current_project_id, $pages);         $prev_page_id = $pages[$current_key-1];          if( isset($prev_page_id) ) {             // previous page exists             return '<a class="previous-project" href="'.get_permalink($prev_page_id).'">'.$html.'</a>';         }      }