def linkable_attributes(*attrs)
      @linkable_attributes ||= []
      if attrs.any?
        @linkable_attributes.map!(&:to_sym).concat(attrs).uniq! if attrs.any?
      end
      @linkable_attributes
    end
def linkable_attributes(*attrs)
      @linkable_attributes ||= []
      if attrs.any?
        @linkable_attributes.map!(&:to_sym).concat(attrs).uniq! if attrs.any?
      end
      @linkable_attributes
    end
Linkable attributes are sent on POST/PUT.