How to serialize/deserialize case classes to/from Json in Play 2.1

Question

I'm trying to serialize/deserialize some case classes to/from Json... and I've troubles when dealing with case classes with just one field (I'm using Play 2.1):

import play.api.libs.json._
import play.api.libs.functional.syntax._

case class MyType(type: String)

object MyType {

  implicit val myTypeJsonWrite = new Writes[MyType] {
    def writes(type: MyType): JsValue = {
      Json.obj(
        "type" -> MyType.type
      )
    }
  }

  implicit val myTypeJsonRead = (
    (__ \ 'type).read[String]
  )(MyType.apply _)
}

The code above always generates the following error message:

[error] /home/j3d/Projects/test/app/models/MyType.scala:34: overloaded method value read with alternatives:
[error]   (t: String)play.api.libs.json.Reads[String] <and>
[error]   (implicit r: play.api.libs.json.Reads[String])play.api.libs.json.Reads[String]
[error]  cannot be applied to (String => models.MyType)
[error]     (__ \ 'method).read[String]
[error]                        ^

I know... a case class that contains just a string does not make much sense... but I need to serialize/deserialize a case class very similar to the one I described above that comes from an external library.

Any idea? Am I missing something? Any help would be really appreciated... I'm getting crazy :-( Thanks.

Answer 1

Json combinators doesn't work for single field case class in Play 2.1 (it should be possible in 2.2)

Pascal (writer of this API) has explained this situation here https://groups.google.com/forum/?fromgroups=#!starred/play-framework/hGrveOkbJ6U

There are some workarounds which works, like this one:

case class MyType(value: String)
val myTypeRead = (__ \ 'value).read[String].map(v => MyType(v)) // covariant map

ps: type is a keyword in Scala, it can't be used as parameter name (but I assume it's just for this example)

edit: This workaround is not yet required with play 2.3.X. The macro works fine.