这个WP_Query 类可以匹配ID和搜索词。一个想法是使用pre_get_posts 用于检测搜索词是否为数字的操作，如果是，则将查询设置为使用附件，同时将搜索作为ID传递。

function wpse223307_allow_search_by_attachment_id( $query ) {

    //Only alter the query if we are in a search screen,...
    if( ! is_search() ) :
        return;
    endif;

    //...the search term has been set...
    if( ! isset( $query->query_vars[\'s\'] ) ) :
        return;
    endif;

    $search_term = $query->query_vars[\'s\'];

    //...and the search term is a number
    if( ! is_numeric( $search_term ) ) :
        return;
    endif;

    //Set the post type and post status to work with attachments (assuming you want to exclude other post types in numeric searches)
    $query->set( \'post_type\', array( \'attachment\' ) );
    $query->set( \'post_status\', array( \'inherit\' ) );

    //Match the search term with the attachment\'s ID and remove it from the query
    $query->set( \'p\', $search_term );
    $query->set( \'s\', \'\' );

}

add_action( \'pre_get_posts\', \'wpse223307_allow_search_by_attachment_id\');