def only(*args)
      return clone if args.flatten.empty?
      args = args.flatten
      if (args & Fields::IDS).empty?
        args.unshift(:_id)
      end
      if klass.hereditary?
        super(*args.push(:_type))
      else
        super(*args)
      end
    end
def only(*args)
      return clone if args.flatten.empty?
      args = args.flatten
      if (args & Fields::IDS).empty?
        args.unshift(:_id)
      end
      if klass.hereditary?
        super(*args.push(:_type))
      else
        super(*args)
      end
    end
Overriden to include _type in the fields.

 @example Limit the fields returned from the database.
   Band.only(:name)

 @param [ Array<Symbol> ] args The names of the fields.

 @return [ Criteria ] The cloned criteria.

 @since 1.0.0