Track changes to model and save results to another model

Question

I'm in a Rails 3.2 app. I want certain fields in a model called Candidate to be saved into an Update model when the admin user changes them via the CRUD (which happens with an update_attributes call in the standard Rails scaffold way).

I've got code in a Candidate model which tracks changes in a before_save filter:

before_save :check_changed
def check_changed
  period_contributions_changed?
end

This is inside candidate.rb, the Candidate model file.

What I'd like is for a changed value in period_contributions and other specified fields to trigger the creation of another record, Update.

An Update would contain the candidate ID, the name of the field that changed, the previous value and the new value.

This seems like it would require the model code calling a method on the Update controller, which seems like bad practice. Is there a best practice for doing this?

Answer 1

ActiveRecord provides some methods that you can make use of

1. changed? -> tells you id the object is changed
2. changed -> gives an array of attributes that changed

3. changed_attributes -> gives you a hash with keys as the changed attributes and values as old value

   before_save :log_changed
   
   def log_changed
     if self.changed?
       self.changed.each do |attr|
         Update.create(:candidate_id => self.id, :field => attr, 
         :new_value => self.attributes[attr], :old_value => self.changed_attributes[attr])
       end
     end
   end