after_update回调问题

Question

I have a model A which has association with another model Company. So, I call it as A.find(5).companies

I want to do something in after_update callback of A. I add some companies in A.find(5).companies and want to know which companies got added in the callback. But in after_update callback, how can I get the list of companies in A.find(5).companies before the update?

Answer 1

You can do this in the on_create callback of model Company . Whenever a new company is added, you can see value of A from this and do your task.

Answer 2

You can create a logic using the created_at and updated_at timings .

Once you will fire after_update callback for model A the updated_at filed of the table will be updated and you can get the list of companies where created_at time is later then the updated at of model A.

Answer 3

.. in your controller.. when updating a model with accepts_nested_attributes_for

def update
  a.assign_attributes(params[:a])
  was_changed = a.companies.any?{|c| c.changed?} 
  a.save
end