I have looked through the Incubator repository and the only reference I see for DBRef support for mongo is with the Mongo\Client.

https://github.com/phalcon/incubator/blob/e35352e27fb25521686da4acc82bbffa208c206b/Library/Phalcon/Db/Adapter/Mongo/DbRef.php

Is DBRef capabilities not available for MongoDB client. If I am missing something, please let me. I see no unit tests covering fetching related documents. If this feature does work and sample code be provided, that would be appreciated.