Play controller serving nested case class as Json

NestedJson.scala

package controllers

case class Root(id: Int, name: String, children: Seq[Child])

case class Child(id: Int, name: String)

object Application extends Controller with Secured{
  
  def test = Action { implicit req =>
    
    //childFmt must go first, otherwise the rootFmt will not compile
    implicit val childFmt = Json.writes[Child]
    implicit val rootFmt = Json.writes[Root]

    val children = Seq(
      Child(1, "child1"),
      Child(2, "child2"),
      Child(3, "child3")
    )
    val root = Root(0, "root", children)

    Ok(Json.toJson(root))
  }
}