Meta Key by Query
$autore = get_the_ID();
$args = array(
'post_type' => 'libri',
'post_status' => 'publish',
'order' => 'DESC',
'orderby' => 'date',
'ignore_sticky_posts' => true,
'posts_per_page' => -1,
'meta_query' => array(
array(
'key' => 'autori',
'value' => '"' . $autore . '"',
'compare' => 'LIKE'
))
);
$libri = new WP_Query( $args );