无法理解为什么validateOpt将返回`None`而不是`JsError`

Question

在下面的代码中，我无法理解为什么validateOpt可能返回值JsSuccess(None)而不是JsError

def getQuestion = silhouette.UserAwareAction.async{ 

    implicit request => {        
      val body: AnyContent = request.body
      val jsonBodyOption: Option[JsValue] = body.asJson

      jsonBodyOption.map((jsonBody:JsValue) => { //body is json
        val personJsonJsResultOption = jsonBody.validateOpt[Person]//check that json structure is correct

        personJsonJsResultOption match {
          case personSuccessOption: JsSuccess[Option[Person]] => { //json is correct
val personOption = personSuccessOption.getOrElse(None) //why would getOrElse return None??
            personOption match {
              case Some(person) => {
...              }
              case None =>{ //I am not sure when this will be triggered.
     ...
                }
              }
            }
          }
          case e: JsError => {
        ...
            }
          }
        }
      })
      .getOrElse(//body is not json
...)
    }
  }

Answer 1

validateOpt的设计认为成功不仅在body提供实际的Person时，而且当Person是null或未提供时。请注意documentation如何解释为什么返回JsSuccess(None)：

  /**
   * If this result contains `JsNull` or is undefined, returns `JsSuccess(None)`.
   * Otherwise returns the result of validating as an `A` and wrapping the result in a `Some`.
   */
  def validateOpt[A](implicit rds: Reads[A]): JsResult[Option[A]]

似乎你的要求是必须始终提供Person才能被认为是成功的，所以在这种情况下应该使用validate而不是validateOpt。