Play json transformers map optional field

Question

I have the following play framework 2.3 json transformer

val transAddress = (
  (__ \ 'address \ 'line1).json.copyFrom( (__ \ 'line1).json.pick ) and
  (__ \ 'address \ 'line2).json.copyFrom( (__ \ 'line2).json.pick ) and
  (__ \ 'address \ 'line3).json.copyFrom( (__ \ 'line3).json.pick ) and

  (__ \ 'address \ 'line4).json.copyFrom( (__ \ 'line4).json.pick ) and

  (__ \ 'address \ 'postcode).json.copyFrom( (__ \ 'postcode).json.pick ) reduce
)

So this:

{
    line1: "My Street",
    line2: "My Borough",
    line3: "My Town",
    line4: "My County"
}

Should transform to this:

{
    address: {
        line1: "My Street",
        line2: "My Borough",
        line3: "My Town",
        line4: "My County"
    }
}

My problem is that in the source json model, line4 is optional, so i only want to map it to address.line4 optionally as well. So:

{
    line1: "My Street",
    line2: "My Borough",
    line3: "My Town"
}

Should also transform to this:

{
    address: {
        line1: "My Street",
        line2: "My Borough",
        line3: "My Town"
    }
}

I have no idea how to do this with these transformers, and can find no similar problem after a lot of googling.

Thanks! Nic

Answer 1

Use Option with readNullable

import play.api.libs.functional.syntax._
import play.api.libs.json._
case class Address(line1: String, line2: String, line3: String, line4: Option[String])

object Address {
  implicit val reads: Reads[Address] = (
      (JsPath \ "line1").read[String] and
      (JsPath \ "line2").read[String] and
      (JsPath \ "line3").read[String] and
      (JsPath \ "line4").readNullable[String]
    )(Address.apply _)
}