public function save( $expires ) {

		// Only save if we have data to save.
		if ( $this->is_clean ) {
			return false;
		}

		global $wpdb;
		$save = $wpdb->query(  // phpcs:ignore: WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching
			$wpdb->prepare(
				"INSERT INTO {$wpdb->prefix}lifterlms_sessions ( `session_key`, `data`, `expires` ) VALUES ( %s, %s, %d )
				ON DUPLICATE KEY UPDATE `data` = VALUES ( `data` ), `expires` = VALUES ( `expires` )",
				$this->get_id(),
				maybe_serialize( $this->data ),
				$expires
			)
		);

		wp_cache_set( $this->get_cache_key( $this->get_id() ), $this->data, $this->cache_group, $expires - time() );
		$this->is_clean = true;

		return (bool) $save;

	}