title: Conditional Association In Doctrine2
body: <p>I have just run myself into this tricky situation.
  I have an entity called Gift.</p>
  
  <p>Now the gift entity needs to have a field called <code>receiver</code> which can be associated with 2 entities <code>RegisteredUser</code> entity OR <code>Guest</code> entity.</p>
  
  <p>The problem here is now how do I define the association for the receiver field!!</p>
  
  <p>I thought of creating an entity called <code>GiftReceiver</code> use inheritance mapping but I cannot map the discriminator to a class which does not extend GiftReceiver.</p>
  
  <p>Am I going the wrong way? Is there a good way to implement this?
  Thanks in advance for your help!! :) </p>