因此，正如克里斯汀在评论中所建议的那样，我首先在寻找一种循环浏览现有帖子的方法。基于this answer, 我创建了一个基本插件，在激活时运行循环。

// Run the loop when the plugin is activated
register_activation_hook(__FILE__, \'update_my_metadata\');
function update_my_metadata(){
$args = array(
    \'post_type\' => \'post\', // Only get the posts
    \'post_status\' => \'publish\', // Only the posts that are published
    \'posts_per_page\'   => -1 // Get every post
);
$posts = get_posts($args);
foreach ( $posts as $post ) {
    // Run a loop and update every meta data
    $month=get_the_date(\'M\');
    $year=get_the_date(\'Y\');
    update_post_meta($post->ID, \'month-field\', $month); echo $month;
    update_post_meta($post->ID, \'year-field\', $year); echo $year;
 }
}

有什么建议吗？