CODEWITHSUNDEEP
jsonscalaplayframeworkplayframework-json
Ende Neu
Ende Neu

Reputation: 15783

Play Json add field which is not present in class

Let's say I have a class like this:

abstract class SomeSuperClass(name: String)
case class SomeClass(someString: String, opt: Option[String]) extends SomeSuperClass("someName")

I want to serialize this class and be able to add the name field, this was my first approach:

implicit def serialize: Writes[SomeClass] = new Writes[SomeClass] {
  override def writes(o: SomeClass): JsValue = Json.obj(
    "someString" -> o.someString,
    "opt" -> o.opt,
    "name" -> o.name
  )
}

This returns null if there's a None, so I changed my implementation following the documentation to this:

implicit def serialize: Writes[SomeClass] = (
  (JsPath \ "someString").write[String] and
  (JsPath \ "opt").writeNullable[String] and
  (JsPath \ "name").write[String]
)(unlift(SomeClass.unapply))

This doesn't compile, it works only if I remove the name field:

[error]   [B](f: B => (String, Option[String], String))(implicit fu: play.api.libs.functional.ContravariantFunctor[play.api.libs.json.OWrites])play.api.libs.json.OWrites[B] <and>
[error]   [B](f: (String, Option[String], String) => B)(implicit fu: play.api.libs.functional.Functor[play.api.libs.json.OWrites])play.api.libs.json.OWrites[B]
[error]  cannot be applied to (api.babylon.bridge.messaging.Command.SomeClass => (String, Option[String]))
[error]       (JsPath \ "opt").writeNullable[String] and

How can I add a field which is not strictly present in a case class and has an optional field?

I'm using play-json 2.3.0.

Upvotes: 2

Views: 1007

Answers (1)

Mikesname
Mikesname

Reputation: 8901

Instead of using the default (compiler generated) unapply method, which knows nothing about your inherited values, you can write your own extractor for the JSON writes which takes a SomeClass instance and returns a (String, Option[String], String) tuple, i.e:

implicit def serialize: Writes[SomeClass] = (
  (JsPath \ "someString").write[String] and
  (JsPath \ "opt").writeNullable[String] and
  (JsPath \ "name").write[String]
)(s => (s.someString, s.opt, s.name))

This gives you:

Json.toJson(SomeClass("foo", None))
// {"someString":"foo","name":"someName"}

Jspm.toJson(SomeClass("foo", Some("bar")))
// {"someString":"foo","opt":"bar","name":"someName"}

Upvotes: 4

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