Transform Value In PlayJSon Mapping

Question

I'm performing a standard mapping of JSON to a case class using PlayJson. I'd like to transform the value that gets mapped to a member, Test.foo below, if the validation succeeds. Is it possible to work that into the definition of a Reads converter?

val json = .....

case class Test(foo:String, bar:String)

val readsTest: Reads[Test] = (
  (__ \ "foo").read[String](minLength(5)) and // And I want to transform this value if the validation succeeds
  (__ \ "bar").read[String](minLength(10))
)(Test.apply _)


json.validate[Test] match {
  case s: JsSuccess[Test] => s.get
  case e: JsError => false
}

Answer 1

Reads.map can do just that, for example, say we want to reverse the value of foo field, then we could call .map(v => v.reverse) on the Reads like so

(__ \ "foo").read[String](minLength[String](5)).map(v => v.reverse)

Here is a working example

val json =
  """
    |{
    |  "foo": "abcdefghijkl",
    |  "bar": "012345678910"
    |}
    |""".stripMargin

case class Test(foo: String, bar: String)

val readsTest: Reads[Test] = (
  (__ \ "foo").read[String](minLength[String](5)).map(v => v.reverse)
  (__ \ "bar").read[String](minLength[String](10))
)(Test.apply _)

Json.parse(json).validate[Test](readsTest)

which outputs

JsSuccess(Test(lkjihgfedcba,012345678910),)