def connected_columns
      @connected_columns ||= begin
        view_columns.keys.map do |field_name|
          datatable.column_by(:data, field_name.to_s)
        end.compact
      end
    end
def connected_columns
      @connected_columns ||= begin
        view_columns.keys.map do |field_name|
          datatable.column_by(:data, field_name.to_s)
        end.compact
      end
    end
helper methods