获取当前文章同分类下的前几篇文章和后几篇文章

代码是参考wp自带的get_adjacent_post函数修改而来，get_adjacent_post函数是wordpress用来获取上一篇和下一篇文章的基本函数。
函数作用：获取当前文章同分类下的前几篇文章和后几篇文章
参数：$previous为true时获取之前的文章,为false的时候获取之后的文章
$number为获取文章数量
函数代码：

//author：ashuwp
function ashu_get_adjacent_posts( $previous = true, $number = 1 ) {
    //global当前文章变量 $post 和数据库操作类wpdb
    global $post, $wpdb;
    if ( empty( $post ) )
        return null;
    $current_post_date = $post->post_date;//当前文章的时间
    $join = '';
    $posts_in_ex_cats_sql = '';
    //加入表
    $join = " INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id INNER JOIN $wpdb->term_taxonomy tt ON tr.term_taxonomy_id = tt.term_taxonomy_id";
    //获取当前文章所属分类,可以同属多个分类,如果是自定义的分类法,将category换成对应的分类法即可
    $cat_array = wp_get_object_terms($post->ID, 'level', array('fields' => 'ids'));
    $join .= " AND tt.taxonomy = 'level' AND tt.term_id IN (" . implode(',', $cat_array) . ")";
    //判断时间是大于还是小雨
    $op = $previous ? '<' : '>';
    //排序
    $order = $previous ? 'DESC' : 'ASC';
    $where = $wpdb->prepare("WHERE p.post_date $op %s AND p.post_type = %s AND p.post_status = 'publish' ", $current_post_date, $post->post_type);
    $sort  = "ORDER BY p.post_date $order LIMIT 0, $number";
    $query = "SELECT p.* FROM $wpdb->posts AS p $join $where $sort";
    $query_key = 'adjacent_post_' . md5($query);
    $result = wp_cache_get($query_key, 'counts');
    if ( false !== $result )
        return $result;
    $result = $wpdb->get_results("SELECT p.* FROM $wpdb->posts AS p $join $where $sort");
    if ( null === $result )
        $result = '';
    wp_cache_set($query_key, $result, 'counts');
    return $result;
}

将该函数放在主题的functions.php文件中即可，调用该函数的时候会返回一个数组，使用示例：

<h4>本篇教程之前的几篇教程是</h4>
            <ul>
            <?php
            $preposts = ashu_get_adjacent_posts(true,3);
            foreach( $preposts as $postt ){
                echo '<li><a href="'.get_permalink($postt->ID).'" title="'.$postt->post_title .'">'.$postt->post_title .'</a></li>';
            };
            ?>
            </ul>
            <h4>本篇教程之后的几篇教程是</h4>
            <ul>
            <?php
            $nextposts = ashu_get_adjacent_posts(false,3);
            foreach( $nextposts as $postt ){
                echo '<li><a href="'.get_permalink($postt->ID).'" title="'.$postt->post_title .'">'.$postt->post_title .'</a></li>';
            };
            ?>
            </ul>