Display every grandchildren 在wordpress支持论坛上似乎非常接近。

以下是提出的解决方案：

<ul>
<?php $all = get_pages();   //You could use $args to retrieve posts how you want.
foreach($all as $all) { 
 if($all->post_parent) { 
  if( get_page($all->post_parent)->post_parent ) { 
   $tp = get_page($all->post_parent);
   if( !get_page( $tp->post_parent )->post_parent) { $grandchild_ids[] = $all->ID; }    //catching all the ids of grandchild or secondchild.
  }
 }
}

//Usual args parameter & WP_Query loop
$args = array(
    \'post_type\' => \'page\',
    \'post_status\' => \'publish\',
    \'posts_per_page\' => 5,
    \'orderby\' => \'rand\',
    \'post__in\' => $grandchild_ids
  );
$my_query = null;
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) { 
    while ($my_query->have_posts()) : $my_query->the_post(); ?>
        <li><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></li>
    <?php endwhile;
} 
wp_reset_query(); ?>
</ul>

总之，你会从所有父母的孙子孙女名单中随机获得5条帖子。

虽然@sri answer 帮助，这里有一个函数，即使深度大于2，也可以获得最深的类别。（摘自并修改自this answer.). 此函数使用wordpress的函数get_ancestors().

function get_deepest_term($post_id){

    $the_terms = get_the_terms( $post_id, \'Category\' );

    if ( $the_terms && ! is_wp_error( $the_terms ) ) {

        $deepest = $the_terms[0];
        $depth = 0;
        $term_depth= 0;

       // Find the deepest term
       foreach( $the_terms as $term ) {
           $term_ancestors = get_ancestors( $term->term_id, \'Category\' );
           if ( $term_ancestors ) {
               $term_depth = count( $term_ancestors );
           }
           else $term_depth= 0;

           if ( $term_depth > $depth ) {
               $depth = $term_depth;
               $deepest = $term;
           }

       } // END: foreach( $the_terms as $term ) 

   }  // END: if ( $the_terms && ! is_wp_error( $the_terms ) ) 

    return $deepest;
}   // END: function get_deepest_term($post_id)

然后，可以使用上述函数循环遍历最深类别的帖子，如下所示（代码取自@sri answer):

<?php

//Usual args parameter & WP_Query loop
$args = array(
    \'post_type\' => \'post\',
    \'post_status\' => \'publish\',
    \'posts_per_page\' => 5,
    \'orderby\' => \'rand\',
    \'post__in\' => array(get_deepest_term( get_the_ID() )->term_id)
);

$my_query = new WP_Query($args);
if( $my_query->have_posts() ) { ?>
   <ul>

       <?php while ($my_query->have_posts()) : $my_query->the_post(); ?>
           <li><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></li>
       <?php endwhile;
      wp_reset_post_data();

} // END: if( $my_query->have_posts() ) ?>
   </ul>

所以，我的问题是，有没有一种方法可以让我获得当前帖子最低级别子类别的ID，但忽略它的父类别？

   $lowest_tier_child_category = get_deepest_term( get_the_ID() )->term_id