playframework scala期货和异步获取数据和操纵对象

Question

我有脑力劳动但在这种情况下不知道该怎么做：

process.flatMap({ case (..., processSteps, ...) =>
      Future.sequence {
        processSteps.map { step =>
            val prerequisiteFuture = processStepPrerequisitesDTO.getProcessStepPrerequisiteProcessTemplateIds(step.id.get)

            prerequisiteFuture.map(prereqTemplates => {
              Future.successful{
                processTemplateDTO.getProessTemplatesForStepPreqrequsites(prereqTemplates).map(pres => {
                  println("Returning something", pres) // they are printed
                  step.stepPrerequisites = Some(pres)
                })
              }
              println("Obviously empty", step.stepPrerequisites)
              step // line x
            })
        }
      }.map { stepTemplates =>
          Ok(Json.obj(
            ...
            "steps" -> stepTemplates,
            ...
          ))
      }
    })

我怎样才能让第x行的step.prerequisites不再为空？谢谢！