scala play 2.1.1 json functional syntax mapping data to a different format

Question

I'm trying to write a custom json serializer using the functional syntax and I can't seem to find the right way to solve this particular problem. I have a couple of joda DateTime objects that I want to write in a specific format for the UI consuming it. Can anyone show me where I've gone wrong?

Here is the case class I am dealing with at the moment, nothing special going on.

case class Banner(
  id: Int = 0,
  ownerId: Int = 0,
  licenseeId: Option[Int] = None,
  statusColor: Option[String] = None,
  content: Option[String] = None,
  displayStart: DateTime = new DateTime(),
  displayEnd: DateTime = new DateTime(),
  created: DateTime = new DateTime(),
  updated: DateTime = new DateTime()
)

These are my imports for the serializer object.

import play.api.libs.json._
import play.api.libs.functional.syntax._
import org.joda.time.DateTime
import org.joda.time.format.DateTimeFormat

First off, the joda DateTime converts to a long just fine implicitly so the macro expander works great if that's all I wanted.

object MySerializers {
  implicit val writesBanner = Json.writes[Banner]
}

What I need is to convert the displayStart and displayEnd objects to a particular string format rather than the long value. This is what I tried to do.

object MySerializers {
  val userDateFormatter = DateTimeFormat.forPattern("MM/dd/yyyy HH:mm a")

  implicit val writesBanner = (
    (__ \ "id").write[Int] and
    (__ \ "ownerId").write[Int] and
    (__ \ "licenseeId").write[Int] and
    (__ \ "statusColor").writeNullable[String] and
    (__ \ "content").writeNullable[String] and
    (__ \ "displayStart").write[DateTime].inmap[String](dt => userDateFormatter.print(dt)) and
    (__ \ "displayEnd").write[DateTime].inmap[String](dt => userDateFormatter.print(dt)) and
    (__ \ "created").write[DateTime] and
    (__ \ "updated").write[DateTime]
  )(unlift(Banner.unapply))
}

But the compiler is not happy about that, so I don't seem to understand the correct way to use the inmap function.

could not find implicit value for parameter fu: 
play.api.libs.functional.InvariantFunctor[play.api.libs.json.OWrites]
[error]     (__ \ "displayStart").write[DateTime].inmap[String](dt =>     
userDateFormatter.print(dt)) and
[error]                                ^

Any advice is much appreciated.

Answer 1

I managed to get this one figured out, I was using the wrong type of functor map operations and had the types I was working with backwards. Here are working reads/writes implementations in the much nicer functional syntax.

implicit val writesBanner = (
    (__ \ "id").write[Int] and
    (__ \ "ownerId").write[Int] and
    (__ \ "licenseeId").writeNullable[Int] and
    (__ \ "statusColor").writeNullable[String] and
    (__ \ "content").writeNullable[String] and
    (__ \ "displayStart").write[String].contramap[DateTime](dt => userDateFormatter.print(dt)) and
    (__ \ "displayEnd").write[String].contramap[DateTime](dt => userDateFormatter.print(dt)) and
    (__ \ "created").write[DateTime] and
    (__ \ "updated").write[DateTime]
  )(unlift(Banner.unapply))

implicit val readsBanner = (
    (__ \ "id").read[Int] and
    (__ \ "ownerId").read[Int] and
    (__ \ "licenseeId").readNullable[Int] and
    (__ \ "statusColor").readNullable[String] and
    (__ \ "content").readNullable[String] and
    (__ \ "displayStart").read[String].fmap[DateTime](dt => DateTime.parse(dt, userDateFormatter)) and
    (__ \ "displayEnd").read[String].fmap[DateTime](dt => DateTime.parse(dt, userDateFormatter)) and
    (__ \ "created").read[DateTime] and
    (__ \ "updated").read[DateTime]
  )(Banner)