Writing complex/nested JSON Writes in Scala PlayFramework

Question

Going to assume that I have two case classes: Child, Parent that look something like:

case class Child()
case class Parent(child: Child)

Assume I've already implemented Writes[Child]. I'd like to implement Writes[Parent].

I'm able to do this using combinators:

implicit val parentWrites: Writes[Parent] = (
   (__ \ "child").write[Child]
)(unlift(Parent.unapply))

But with the following approach, the compiler complains that it's seeing the type Child while expecting a JsValueWrapper:

implicit val parentWrites = new Writes[Parent] {
   def writes(parent: Parent) = Json.obj(
      "child" -> parent.child
   )
}

Hoping someone can help me understand how to implement a Writes[Parent] without using combinators.

What is the structure of Parent and Child? Also what do you mean by "can't get it to work"? What is the error? — Michael Zajac
– Michael Zajac, Commented Mar 20, 2015 at 19:25
I've clarified the question as you've asked. The classes aren't interesting at all. I just haven't figured out how to write the writes function for Writes[Parent] correctly without using combinators. — Nadir Muzaffar
– Nadir Muzaffar, Commented Mar 20, 2015 at 20:33
Try wrapping parent.child with this: Json.toJson(parent.child) — goralph
– goralph, Commented Mar 20, 2015 at 22:06
Might be helpful: playframework.com/documentation/2.0/ScalaJson See: converting a Scala value the Json — jspacek
– jspacek, Commented Mar 20, 2015 at 22:11

Vikas Pandya · Accepted Answer · 2015-03-21 21:00:47Z

1

This does work for me without any compile issues.

import play.api.libs.json._

case class Child(t: String)
case class Parent(child: Child)

implicit val parentWrites = new Writes[Parent] {
  def writes(parent: Parent) = Json.obj("child" -> parent.child)
}

If you are still having trouble, it would be useful if you can share your complete sample with stacktrace.

answered Mar 21, 2015 at 21:00

Vikas Pandya

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1 Comment

Nadir Muzaffar Over a year ago

Yes this worked for me as well. It seems that IntelliJ is simply complaining to me about a JsValueWrapper.

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