如何使用Scala组合器读取case类中的可选json值

Question

I am trying to process JSON which can optionally have 'info' and its contains. Which is captured in the following case class and the combinator to read the JSON in object. But the code fails to compile. Is there better way of handling this? Info can be empty.

case class Info(sometimestamp: Option[Long])

object Info {
  implicit val InfoReads: Reads[Info] = (
    (JsPath \ "sometimestamp").readNullable[Long]
  )(Info.apply _)
}

{
  ...
  "info" : {
    "sometimestamp" : 1414535323436
  }
}

Compilation error:

found   : play.api.libs.json.Reads[Option[Long]]
[error]  required: play.api.libs.json.Reads[models.Payload.Info]
[error]   ) (Info.apply _)

scala version: 2.11.2

thanks,

Answer 1

I don't think the functional syntax for combinators work when you're not actually combining anything. This does, however:

implicit val InfoReads: Reads[Info] = 
    (JsPath \ "sometimestamp").readNullable[Long].map(Info(_))

You might also consider just using the JSON inception macro for such a simple case class:

implicit val InfoReads: Reads[Info] = Json.reads[Info]