@Document
Obj1 {
  @DbRef Obj2 obj2Ref;
@Document
Obj2 {
  String foo;
then one could do the following query:
 query
    .where(QObj1.obj2Ref.foo.eq("Bob"))
    .list()
          
This sounds like a valid addition, but might be quite difficult to implement, since dbref on database level doesn't seem to be supported.
So it's multiple nested queries or maybe map-reduce. Do you see other implementation options?
          
Here I'd also prefer to apply some more explicit joining
query.join(doc.obj2Ref, obj2).on(obj2.foo.eq("Bob"))
This could be continued with a where-clause if additional constraints are needed. This separates the query layers quite clearly. Is something like this ok?
public void Double2() {
    assertEquals("Mike", where()
            .join(user.friend(), friend).on(friend.firstName.eq("Mary"))
            .join(user.enemy(), enemy).on(enemy.firstName.eq("Ann"))
            .singleResult().getFirstName());
@Test
public void Deep() {
    // Mike -> Mary -> Jane
    assertEquals("Mike", where()
            .join(user.friend(), friend).on(friend.firstName.isNotNull())
            .join(friend.friend(), friend2).on(friend2.firstName.eq("Jane"))
            .singleResult().getFirstName());
i would like to do the same with list of @DBRef like this :
@DBRef
private List<FileSys> registeredChannels = new ArrayList<FileSys>();
my request >  QProfile.profile.registeredChannels.contains(channel)
(channel is an FileSys object)
always return an empty list
please, help me
          
@timowest I haven't had a chance to try out the new feature yet... however FYI the spring-data mongodb guys are thinking about how to use this from the spring-data mongodb querydsl integration. You might have some useful thoughts on it...
https://jira.springsource.org/browse/DATAMONGO-362
          
@timowest is there a possibility to construct query with OR between join predicates?
public class Car {
    BigInteger id;
    String name;
    @DBRef
    Engine engine;
    @DBRef
    Radio radio;
public class Radio {
    BigInteger id;
    Boolean rds;
public class Engine {
    BigInteger id;
    Integer power;
And I would like to get cars with engine more then 100 power or cars with radios with rds.