My JSON reads is not compiling when there is an Option[Instant] property on my case class

Question

How do I write the json reads for a class that has an option Instant property?

case class User(id: Int, joined: Option[Instant])

My IDE is showing the error:

No implicit found for parameter: Reads[Option[Instant]]

implicit val userReads: Reads[User] = (
  (__\ "id").read[Int] and 
  (__ \ "joined").read[Option[Instant]]
 )(User.apply _ )

If I remove the Option than the Instant works fine.

Why doesn't it allow the options for an Instant?

Answer 1

You should not try to resolve Option[T] in such case, but use readNullable.

import java.time.Instant

case class User(id: Int, joined: Option[Instant])

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

implicit val userReads: Reads[User] = (
  (__ \ "id").read[Int] and 
  (__ \ "joined").readNullable[Instant]
 )(User.apply _)

Also, it easier in such case to use the provided macro:

import java.time.Instant

case class User(id: Int, joined: Option[Instant])

import play.api.libs.json._

implicit val userReads: Reads[User] = Json.reads[User]