def attribute_will_change!(attr)
      unless changed_attributes.key?(attr)
        changed_attributes[attr] = read_raw_attribute(attr).__deep_copy__
      end
    end
def attribute_will_change!(attr)
      unless changed_attributes.key?(attr)
        changed_attributes[attr] = read_raw_attribute(attr).__deep_copy__
      end
    end
Flag an attribute as going to change.

 @example Flag the attribute.
   model.attribute_will_change!("name")

 @param [ String ] attr The name of the attribute.

 @return [ Object ] The old value.

 @since 2.3.0