Unable to convert generic case class to json using “writes”

Question

I have a class which I want to be able to convert to json:

case class Page[T](items: Seq[T], pageIndex: Int, pageSize: Int, totalCount: Long)

object Page {

  i         


        

Answer 1

You can define Format[Page[T]] for generic case class Page[T] like this:

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

implicit def pageFormat[T: Format]: Format[Page[T]] =
  ((__ \ "items").format[Seq[T]] ~
    (__ \ "pageIndex").format[Int] ~
    (__ \ "pageSize").format[Int] ~
    (__ \ "totalCount").format[Long])(Page.apply, unlift(Page.unapply))

Although this solution requires more typing, it keeps your case class Page[T] clear of implicit parameter list or need to define concrete subclasses of Page[T].