Scala编译错误-找不到类型为证据的隐式值

Question

我在以下案例类中使用Spray json序列化

case class ActivationMessage(override val transid: TransactionId,
                             action: FullyQualifiedEntityName,
                             revision: DocRevision,
                             user: Identity,
                             activationId: ActivationId,
                             activationNamespace: EntityPath,
                             content: Option[JsObject],
                             cause: Option[ActivationId] = None,
                             traceMetadata: Option[SpanMetadata] = None
                            ) extends Message {

  def meta = JsObject("meta" -> {
    cause map {
      c => JsObject(c.toJsObject.fields ++  activationId.toJsObject.fields)
    } getOrElse {
      activationId.toJsObject
    }
  })

  override def serialize = ActivationMessage.serdes.write(this).compactPrint

  override def toString = {
    val value = (content getOrElse JsObject()).compactPrint
    s"$action?message=$value"
  }

  def causedBySequence: Boolean = cause.isDefined
}

object ActivationMessage extends DefaultJsonProtocol {
  def parse(msg: String) = Try(serdes.read(msg.parseJson))
  private implicit val fqnSerdes = FullyQualifiedEntityName.serdes
  implicit val serdes = jsonFormat9(ActivationMessage.apply)
}

我收到编译错误提示-找不到类型为ActivationMessage.JF[Option[com.github.levkhomich.akka.tracing.SpanMetadata]]证据参数的隐含值

如果我从构造函数中删除最后一个参数，并使用jsonFormat8，那么一切都会编译正常。 如何在没有任何编译问题的情况下添加此额外参数？

Answer 1

编译器找不到JsonFormat的隐式SpanMetadata 。 尝试：

...
object ActivationMessage extends DefaultJsonProtocol {
  ...
  private implicit val spanMetaSerdes = jsonFormat4(SpanMetadata.apply)
  implicit val serdes = jsonFormat9(ActivationMessage.apply)
}