Adding more data on saving 'has_many :through' associated records by keeping use of the "RoR magical\automatic way"

I am using Ruby on Rails 3.0.7 and I followed this post about handling an "has_many :through => checkboxes" in which, in order to create user-group relationship records for membership purposes, is just passed a group_ids parameter (that is an array of id values) from check box input fields to the @user.save method. Using that code all works good in a "RoR magical\automatic way" (RoR set properly user_id values in the related memberships database table).

However, on saving, I would like to add some extra information to Membership r开发者_JAVA百科ecords. That is, (following that post content) when it creates the associated records in the memberships database table (which database table has id, user_id and group_id columns) I would like to save an extra description information (which, for example, can be represented by a description column in that memberships table).

Is it possible to accomplish that by keeping use of the "RoR magical\automatic way"?

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I would use the ActiveRecord Callbacks to achieve this :

http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html