title: Get ID of the object saved with association
body: <p>Here is my scenario:
  I have three models <code>Subscriber, Subscription, Plan</code>, with <code>has_many :through</code> relationship 
  between Subscriber and Plans.
  A subscriber can have multiple plans with one active plan. Whenever a subscriber selects a plan I save it using <code>accepts_nested_attributes_for :subscriptions</code>. I get one plan from the form. 
  Now my problem is I want to get the ID of the record created in subscriptions table.</p>
  
  <p>Currently I am retrieving it by finding all subscriptions for the subscriber ordered descending on date created and taking first from the resultset. 
  Is there any direct method to do this?</p>