title: JDO unowned many to many relationship
body: <p>I am creating a Cloud Endpoint in Google App Engine with JDO. I have two entities. The User entity contains a list of groups. The group entity contains a list of members which are user entities.</p>
  
  <p><strong>User Entity:</strong></p>
  
  <pre><code>@PersistenceCapable(identityType = IdentityType.APPLICATION) public class USER {
          @PrimaryKey
          @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
          Key userid;
  
          @Persistent
          String name; 
  
          @Persistent
          private Set&lt;GROUP&gt; groups; //getters setters
  </code></pre>
  
  <p><strong>Group Entity</strong></p>
  
  <pre><code>@PersistenceCapable(identityType = IdentityType.APPLICATION) public class GROUP {
          @PrimaryKey
          @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
          Key groupid;
  
          @Persistent
          String name;  
  
          @Persistent
          private Set&lt;USER&gt; members; //getters setters
  </code></pre>
  
  <p><strong>My API Method</strong></p>
  
  <pre><code>@ApiMethod(name = "INSERT_CIRCLE")
      public wmcircle insertcircle(CIRCLE circle) {
          PersistenceManager mgr = getPersistenceManager();
          try {
              if (contains(circle)) {
                  throw new EntityExistsException("Object already exists");
              }
  
              mgr.makePersistent(circle);
          } finally {
              mgr.close();
          }
          return circle;
      }
  </code></pre>
  
  <p>When I create a group GAE creates the user entities which the circle owns and sets the relationship but thats not the behavior I want. I want that I can set the relationship to existing user entities.</p>