def to_csv(columns: nil)
      attributes = if columns
                     self.columns & columns.map(&:to_sym)
                   else
                     self.columns
                   end

      ::CSV.generate_line(attributes)
    end
def to_csv(columns: nil)
      attributes = if columns
                     self.columns & columns.map(&:to_sym)
                   else
                     self.columns
                   end

      ::CSV.generate_line(attributes)
    end
Header as CSV-string
 @return [String] CSV-string representation.