WordPress通过标签添加相关文章功能

<h3>相关文章</h3>
<ul class="related_posts">
<?php
$post_num = 10;
$exclude_id = $post->ID;
$posttags = get_the_tags(); $i = 0;
if ( $posttags ) {
$tags = ''; foreach ( $posttags as $tag ) $tags .= $tag->term_id . ',';
$args = array(
'post_status' => 'publish',
'tag__in' => explode(',', $tags),
'post__not_in' => explode(',', $exclude_id),
'caller_get_posts' => 1,
'orderby' => 'comment_date',
'posts_per_page' => $post_num,
);
query_posts($args);
while( have_posts() ) { the_post(); ?>
<li><a rel="bookmark" href="<?php the_permalink(); ?>" title="<?php the_title(); ?>" target="_blank"><?php the_title(); ?></a></li>
<?php
$exclude_id .= ',' . $post->ID; $i ++;
} wp_reset_query();
}
if ( $i < $post_num ) {
$cats = ''; foreach ( get_the_category() as $cat ) $cats .= $cat->cat_ID . ',';
$args = array(
'category__in' => explode(',', $cats),
'post__not_in' => explode(',', $exclude_id),
'caller_get_posts' => 1,
'orderby' => 'comment_date',
'posts_per_page' => $post_num - $i
);
query_posts($args);
while( have_posts() ) { the_post(); ?>
<li><a rel="bookmark" href="<?php the_permalink(); ?>"  title="<?php the_title(); ?>" target="_blank"><?php the_title(); ?></a></li>
<?php $i++;
} wp_reset_query();
}
if ( $i  == 0 )  echo '<li>没有相关文章!</li>';
?>
</ul>