Ruby on rails, Change column value on update of other column value

问题

I have two columns related to each other in a Rails model:

Article.body
Article.body_updated_on

I want to change the Article.body_updated_on to Time.now, every time Article.body is updated. If any other fields updated nothing needs to be happen.

回答1:

Just add before save callback to your Article model

class Article < ActiveRecord:Base

  before_save :update_body_modified

private       # <--- at bottom of model

  def update_body_modified
    self.body_updated_on = Time.now if body_changed?
  end
end

回答2:

You can either override the default setter for body, or better yet, use a callback to set it just before update. You could choose from several options: before_save, before_update ... depending on exactly when you want it.

 before_save do |article|
   article.body_updated_on = Time.now if article.body_changed?
 end

来源：https://stackoverflow.com/questions/12397776/ruby-on-rails-change-column-value-on-update-of-other-column-value