public function processWhoColumns($types, & $row, $timestamp = null) {
		if ($types === 'all') $types = array_keys($this->who);
		if (!is_array($types)) $types = [$types];
		if (empty($timestamp)) $timestamp = \Format::now('timestamp');
		foreach ($types as $type) {
			if (!empty($this->who[$type])) {
				// timestamp
				$row[$this->column_prefix . $type . '_timestamp'] = $timestamp;
				// user #
				$row[$this->column_prefix . $type . '_user_id'] = \User::id();
			} else if ($type == 'optimistic_lock') {
				if ($this->optimistic_lock) {
					$row[$this->optimistic_lock_column] = $timestamp;
				}
			}
		}
	}