set_original_value (DataMapper::Property)

    # File lib/dm-core/property.rb, line 522
        def set_original_value(resource, original)
          original_attributes = resource.original_attributes
          original            = self.value(original)

          if original_attributes.key?(self)
            # stop tracking the value if it has not changed
            original_attributes.delete(self) if original == original_attributes[self] && resource.saved?
          else
            original_attributes[self] = original
          end
        end