way1.scala

trait Shortcut { self: Controller =>

  def withEvent[T](eventId: String)(block: Event => Future[T]): Future[T] = {
    EventRepository.getByUuid(eventId).flatMap {
      case Some(event) => block(event)
      case None => Future.successful(NotFound("event not found"))
    }
  }

  def withSession[T](sessionId: String)(block: Session => Future[T]): Future[T] = {
    SessionRepository.getByUuid(eventId).flatMap {
      case Some(session) => block(session)
      case None => Future.successful(NotFound("session not found"))
    }
  }

}

object Sessions extends SilhouetteEnvironment with Shortcut {

  def details(eventId: String, sessionId: String) = SecuredAction.async { implicit req =>
    withEvent(eventId) { event =>
      withSession(sessionId) { session =>
        Future.successful(Ok(views.html.Sessions.details(session, event)))
      }
    }
  }

  def doUpdate(eventId: String, sessionId: String) = SecuredAction.async { implicit req =>
    implicit val user = req.identity

    withEvent(eventId) { event =>
      withSession(sessionId) { session =>
        createForm.bindFromRequest.fold(
          formWithErrors => Future(BadRequest(views.html.Sessions.update(formWithErrors, session, event))),
          formData => SessionRepository.update(sessionId, formData).map { err =>
            Redirect(controllers.routes.Sessions.details(eventId, sessionId))
          })
      }
    }
  }

Nice ! I like this way (quite composable) but it seems that event & session are not fetched in parallel...

I added your suggestion to my gist : https://gist.github.com/loicknuchel/faa974c3661351b73227