[Cases] Restrict query to allowed post IDs

function cases_restrict_query_to_allowed_post_ids( $where, $query ) {
    global $wpdb;

    if ( 'cases' != $query->get( 'post_type' ) )
        return $where;

    $posts = array( ... );
    $where .= " AND $wpdb->posts.ID IN (" . implode( ',', $posts ) . ")";

    return $where;
}
add_filter( 'posts_where', 'cases_restrict_query_to_allowed_post_ids', 10, 2 );