def convert_key key
      case key
      when Symbol
        key
      when String
        sym = key.to_sym
        if self.metadata[ sym ]
          sym
        else
          key
        end
      else
        key
      end
    end
def convert_key key
      case key
      when Symbol
        key
      when String
        sym = key.to_sym
        if self.metadata[ sym ]
          sym
        else
          key
        end
      else
        key
      end
    end
#to_data