def sortable_fields_for(model)
      if model.respond_to?(:sortable_fields)
        model.sortable_fields.map(&:to_sym)
      elsif model.respond_to?(:column_names)
        model.column_names.map(&:to_sym)
      else
        []
      end
    end
def sortable_fields_for(model)
      if model.respond_to?(:sortable_fields)
        model.sortable_fields.map(&:to_sym)
      elsif model.respond_to?(:column_names)
        model.column_names.map(&:to_sym)
      else
        []
      end
    end
Overridable method for available sortable fields