def reindex
      @tags = {}
      self.each_with_index do |field, i|
        @tags[field.tag] ||= []
        @tags[field.tag] << i
      end
      @clean = true
    end
def reindex
      @tags = {}
      self.each_with_index do |field, i|
        @tags[field.tag] ||= []
        @tags[field.tag] << i
      end
      @clean = true
    end
Rebuild the HashWithChecksumAttribute with the current
 values of the fields Array