Error working with JSON in Play 2

Question

I am trying to serialize / deserialize using JSON and the Play Framework 2.1.0 and Scala 2.10. I am using Anorm, and I have a pretty simple Object that I want to store in a database. The Order is very simple: ``` case class Order(id: Pk[Long] = NotAssigned, mfg: String, tp: String) ``` In my controller, I am trying to build a REST interface to be able to accept and send an Order instance (above) as JSON. In there, I have the following code: ``` implicit object PkFormat extends Format[Pk[Long]] { def reads(json: JsValue):Pk[Long] = Id(json.as[Long]) def writes(id: Pk[Long]):JsNumber = JsNumber(id.get) } ``` However, this is failing to compile when I run "play test" with the following: overriding method reads in trait Reads of type (json: play.api.libs.json.JsValue)play.api.libs.json.JsResult[anorm.Pk[Long]]; [error] method reads has incompatible type [error] def reads(json: JsValue):Pk[Long] = Id(json.as[Long]) Does anyone know why this is happening? I have a lot of experience with JAX…

Accepted Answer

`play.api.libs.json.Reads` trait defines `reads` method as:

```
def reads(json : play.api.libs.json.JsValue) : play.api.libs.json.JsResult[A]
```

Therefore, the response of reads method is expected to be `JsResult[A]`, not `A`; that is, `JsResult[Pk[Long]]` and not `Pk[Long]`. In a case of success, you'll want to return this:

```
implicit object PkFormat extends Format[Pk[Long]] {
    def reads(json: JsValue):JsResult[Pk[Long]] = JsSuccess(Id(json.as[Long]))
    def writes(id: Pk[Long]):JsNumber = JsNumber(id.get)
}
```

Error working with JSON in Play 2

Solution

Problem