WordPress实现更完善的文章相关推荐功能

global $post;
$pid = $post->ID;//当前文章的 ID
$tags = [];
$limit = 6;//自定义数量
$post_tags = get_the_terms($pid,'post_tag');
if ( !empty($post_tags) && !is_wp_error($post_tags) ) {
	$tags = wp_list_pluck($post_tags, 'term_id');
}
$related_args = [
	'ignore_sticky_posts' => 1,
	'post_type' => 'post',
	'posts_per_page' => $limit,
	'post_status' => 'publish',
	'post__not_in' => [$pid],
	'tag__in' => $tags,
];
$relateds = new WP_Query($related_args);
$post_count = $relateds->post_count;
$output = '<ul>';
if($relateds->have_posts()){
	while($relateds->have_posts()){
		$relateds->the_post();
		$output .= '<li><a href="'.get_permalink().'">'.get_the_title().'</a></li>';
	}
	if($post_count<$limit){//数量还不够
		wp_reset_postdata();
		$limit = $limit - $post_count;//还差几条数据
		$pids = wp_list_pluck($relateds->posts,'ID');//获取已有文章 ID
		$pids = array_merge([$pid],$pids);//合并文章 ID
		$catids = wp_list_pluck(get_the_category($pid),'term_id');//分类 ID
		$related_args = [
			'ignore_sticky_posts' => 1,
			'post_type' => 'post',
			'posts_per_page' => $limit,
			'post_status' => 'publish',
			'post__not_in' => $pids,
			'category__in' => $catids,
		];
		$relateds = new WP_Query($related_args);
		$post_count = $relateds->post_count;
		if($relateds->have_posts()){
			while($relateds->have_posts()){
				$relateds->the_post();
				$output .= '<li><a href="'.get_permalink().'">'.get_the_title().'</a></li>';
			}
		}
	}//数量还不够
	if($post_count<$limit){//还不够
		wp_reset_postdata();
		$limit = $limit - $post_count;//还差数据
		$pids = array_merge($pids,wp_list_pluck($relateds->posts,'ID'));//合并文章 ID
		$related_args = [
			'ignore_sticky_posts' => 1,
			'post_type' => 'post',
			'posts_per_page' => $limit,
			'post_status' => 'publish',
			'post__not_in' => $pids,
		];
		$relateds = new WP_Query($related_args);
		if($relateds->have_posts()){
			while($relateds->have_posts()){
				$relateds->the_post();
				$output .= '<li><a href="'.get_permalink().'">'.get_the_title().'</a></li>';
			}
		}
	}//还不够
}
wp_reset_postdata();
$output .= '</ul>';
echo $output;