玩2.1 特征的Json序列化

Question

Play 2.1 (Json.format[...]) 中的实验性“Inception”功能仅适用于案例类（请参阅here）。如何为特征编写隐含的自定义格式。我有以下构造：

sealed trait Plan {
  def id: String
  def name: String
  def apps: Int
  def users: Int
  def testruns: Int
  def price: Int
  def prio: Int
}

以及以下扩展特征计划的案例类。

case class Start(
                  id: String = "start",
                  name: String = "Start",
                  apps: Int = 1,
                  users: Int = 1,
                  testruns: Int = 10,
                  price: Int = 99,
                  prio: Int = 30) extends Plan

case class Pro(
                id: String = "pro",
                name: String = "Pro",
                apps: Int = 2,
                users: Int = 5,
                testruns: Int = 25,
                price: Int = 299,
                prio: Int = 20) extends Plan

case class Premium(
                    id: String = "premium",
                    name: String = "Premium",
                    apps: Int = -1,
                    users: Int = -1,
                    testruns: Int = -1,
                    price: Int = 799,
                    prio: Int = 10) extends Plan

现在我需要在 Plan 伴随对象中编写我的自定义隐式格式 val。我试过了：

object Plan {
  implicit val planFormats = (
    (__ \ "id").format[String] and
    (__ \ "name").format[String] and
    (__ \ "apps").format[Int] and
    (__ \ "users").format[Int] and
    (__ \ "testruns").format[Int] and
    (__ \ "price").format[Int] and
    (__ \ "prio").format[Int]
  )(Plan.apply, unlift(Plan.unapply))
}

但是，特征没有 apply 或 unapply 方法。在 Play 2.1 中为 json 序列化提供隐式 val 的正确方法是什么？

Answer 1

您只需提供您自己的函数，从给定值创建一个新实例。

本质上是作为工厂的特征的伴随对象。

object Plan {
  def apply(id: String, name: String, ...) = id match {
    case "pro" => new Pro(id, name, ...)
    ...
  }

  def unapply(p: Person): Option[(String, String, ...)] = ...
}

Answer 2

你为什么要使用 Traits 和实现案例类？

为什么不使用类的实例，例如：

case class Plan (
  id: String,
  name: String,
  apps: Int,
  users: Int,
  testruns: Int,
  price: Int,
  prio: Int
)

val start = new Plan("start", "Start", 1, 1, 10, 99, 30)
val pro = new Plan("pro", "Pro", 2, 5, 25, 299, 20)
val premium = new Plan("premium", "Premium", -1, -1, -1, 799, 10)

然后，您可以保留您的 Json 格式化程序：

object Plan {
  implicit val planFormats = (
    (__ \ "id").format[String] and
    (__ \ "name").format[String] and
    (__ \ "apps").format[Int] and
    (__ \ "users").format[Int] and
    (__ \ "testruns").format[Int] and
    (__ \ "price").format[Int] and
    (__ \ "prio").format[Int]
  )(Plan.apply, unlift(Plan.unapply))
}