code: public <TT> TT fetch(Class<TT> anotherClazz) {
          return r.query(anotherClazz).fetch(this);
      }
docs: Fetch from datastore and cast to given childClazz (no cache is performed)
  
  @param anotherClazz the clazz to cast to
  @param <TT>         The generic parameter of the child clazz
  @return the fetched entity