我正在编写一个插件，将电子邮件附件保存到自定义磁盘文件夹，然后将它们作为附件添加到自定义帖子类型中。到目前为止，这一切都正常，但我需要保存几个元数据值。元数据将始终相同（到目前为止），并且需要在任何附件文件类型（.zip，.jpg，.txt等）上
任何人都可以告诉我如何在此代码中添加元数据键/值：
$filename = $attachment['filename'];
$mimetype = $attachment['mimetype'];
$data = $attachment['data'];
$upload = wp_upload_bits( $filename, null, $data );
if ( ! $upload['error'] ) {
$attachment_data = array(
'guid' => trailingslashit( $upload['url']) . basename( $filename ),
'post_mime_type' => $mimetype,
'post_parent' => $post_id,
'post_title' => preg_replace( '/\.[^.]+$/', '', basename( $filename ) ),
'post_content' => '',
'post_status' => 'inherit',
);
$attachment_id = wp_insert_attachment( $attachment_data, $upload['file'], $post_id );
if ( is_wp_error( $attachment_id ) ) {
return false;
} else {
$attach_data = wp_generate_attachment_metadata( $attachment_id, $upload['file'] );
wp_update_attachment_metadata( $attachment_id, $attach_data );
return true;
}
}