scala - Spray-json序列化继承案例类

Question

我有以下涉及继承的类结构

sealed trait GeometryObject
case class Point(coordinates: Array[Double],`type` :GeometryObjectsType) extends GeometryObject

case class Polygon(coordinates: Array[Array[Array[Double]]],`type` :GeometryObjectsType) extends GeometryObject

我的协议(protocol)如下所示:

object GeoJsonProtocol extends DefaultJsonProtocol {
  implicit val geometryObjectsTypeFormat = GeometryObjectsTypeFormat
  implicit val polygonFormat = jsonFormat2(Polygon)
  implicit val pointFormat = jsonFormat2(Point)
}

收到错误 - 找不到 GeometryObject 类型的证据参数的隐式值。

有没有办法处理这个问题并保持继承灵活性？

Answer 1

需要类层次结构父格式如下:

object GeometryObjectLeafFormats extends DefaultJsonProtocol{
  implicit val geometryObjectsTypeFormat = GeometryObjectsTypeFormat
  implicit val polygonFormat = jsonFormat2(Polygon)
  implicit val pointFormat = jsonFormat2(Point)
}

object GeometryObjectFormat extends JsonFormat[GeometryObject] {
  import GeometryObjectLeafFormats._
  override def read(json: JsValue): GeometryObject = json match {
    case known:JsObject if known.fields.contains("type") =>
      known.fields.get("type").get match{
        case JsString(PointType.value) => pointFormat.read(known)
        case JsString(PolygonType.value) => polygonFormat.read(known)
        case unknown => deserializationError(s"unknown GeometryObject: ${unknown}")
      }
    case unknown => deserializationError(s"unknown GeometryObject: ${unknown}")
  }

  override def write(obj: GeometryObject): JsValue = obj match {
    case x:Point => pointFormat.write(x)
    case x:Polygon=> polygonFormat.write(x)
    case unrecognized => serializationError(s"Serialization problem ${unrecognized}")
  }
}

注意:我有单独的类层次结构，表示序列化为类型字段的类型，为了使类层次结构序列化正常工作，这是必需的。