Json4s-提取以基于种类属性纠正特征实现

Question

我具有许多实现的特征。当为json格式时，您可以通过kind属性轻松区分它们。有什么简单的方法让json4s根据该属性选择正确的实现？ 我宁愿避免编写庞大的自定义序列化程序来分别处理每种情况。

我希望这样的事情可以工作：

class ExampleTest extends WordSpecLike with Matchers {

  implicit val formats: Formats = DefaultFormats + new CarSerializer

  val teslaJson =
    """
      |{
      | "name": "Tesla",
      | "kind": "electric",
      | "batteryCapacity": 250.0
      |}
    """.stripMargin
  val bmwJson =
    """
      |{
      | "name": "BMW",
      | "kind": "petrol",
      | "tankCapacity": 70.0
      |}
    """.stripMargin

  val tesla = ElectricCar(
    "Tesla", "electric", 250.0
  )

  val bmw = PetrolCar(
    "BMW", "petrol", 70.0
  )

  "JSON4s" should {
    "extract electric car" in {
      parse(teslaJson).extract[ElectricCar] should be(tesla)
    }
    "extract petrol car" in {
      parse(bmwJson).extract[PetrolCar] should be(bmw)
    }

    "extract electric car with CarSerializer" in {
      parse(teslaJson).extract[Car] should be(teslaJson)
    }
  }

}

class CarSerializer extends CustomSerializer[Car](_ => ( {
  case car: JObject =>
    car \ "kind" match {
      case JString(v) if v == "electric" => car.extract[ElectricCar]
      case JString(v) if v == "petrol" => car.extract[PetrolCar]
    }
}, {
  case car: Car => Extraction.decompose(car)
}))

sealed trait Car {
  def name: String

  def kind: String
}

case class ElectricCar(
  name: String,
  kind: String,
  batteryCapacity: Double
) extends Car

case class PetrolCar(
  name: String,
  kind: String,
  tankCapacity: Double
) extends Car

不幸的是，它不起作用，因为extract和decompose函数要求存在隐式格式，但是串行化器本身是格式的一部分。