title: Callback to method in different model
body: <p>I have models Group, Membership and User. Connected with a has_many :through association.
  Route wise, membership is nested inside group.</p>
  
  <p>What I want is that whenever someone joins or leaves the group (ie. on create or destroy membership), to initiate a check on the group to check what the dominating language is (this is an attribute in the User model) and update the language attribute in the Group model.</p>
  
  <p>I have a method called define_language in the Group model which seems to work independently.</p>
  
  <p>Now I need to call this method from the Membership model, I was thinking to do this with an <strong>after_save callback</strong>, but I'm having trouble <strong>referencing it to the method in the (different) Group model</strong>.</p>
  
  <p>I put this method in the Group model and not the Membership model as I feel semantically it has little to do with the membership. Is this assumption wrong? How would I go about this problem in an efficient way?</p>