private function migrateFromLegacy()
    {
        if (!$this->database->fieldExists('bootstrap_grid', 'tl_content')
            && $this->database->fieldExists('columnset_id', 'tl_content')
        ) {
            $this->database->query(
                'ALTER TABLE tl_content ADD bootstrap_grid int(10) unsigned NOT NULL default \'0\';'
            );
            $this->database->query('UPDATE tl_content SET bootstrap_grid=columnset_id WHERE bootstrap_grid = 0');
        }
    }