title: How to model social graph in Java
body: <p>Very simple scenario</p>
  
  <p>N users, each user can have 0 .. N - 1 friends (who are also users)</p>
  
  <p>How can I model this in <em>Java</em> for AppEngine data store</p>
  
  <p>Scenario to consider</p>
  
  <ul>
  <li>user x and user y become friends (so both need update their own status, in a transaction</li>
  </ul>