我想设置一个图片作为一个职位的特色图像。我发现这段代码在WordPress的文档，它保存在上传目录的图像，但图像没有设置为特色图像的职位（37在代码）了。
你能帮我看一下吗？谢谢

<?php
  $wp_filetype = wp_check_filetype(basename($filename), null );
  $wp_upload_dir = wp_upload_dir();
  $attachment = array(
     'guid' => $wp_upload_dir['url'] . '/' . basename( $filename ), 
     'post_mime_type' => $wp_filetype['type'],
     'post_title' => preg_replace('/\.[^.]+$/', '', basename($filename)),
     'post_content' => '',
     'post_status' => 'inherit'
  );
  $attach_id = wp_insert_attachment( $attachment, $filename, 37 );
  // you must first include the image.php file
  // for the function wp_generate_attachment_metadata() to work
  require_once(ABSPATH . 'wp-admin/includes/image.php');
  $attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
  wp_update_attachment_metadata( $attach_id, $attach_data );
?>