def columns=(v)
      DataTypeValidator.validate "#{self.class}.columns", [Array], v
      v.each do |ref|
        DataTypeValidator.validate "#{self.class}.columns[]", [String], ref
      end
      @columns = v
    end
def columns=(v)
      DataTypeValidator.validate "#{self.class}.columns", [Array], v
      v.each do |ref|
        DataTypeValidator.validate "#{self.class}.columns[]", [String], ref
      end
      @columns = v
    end
(see #columns)