Conditional mapping in play scala - validation

Question

Using play 2.x, I have the following Form mapping:
val relocationDtoForm: Form[RelocationDto] = Form(
mapping(
"_type" -> text,
"sourceToken" -> text,
"exchange" -> optional(jodaDate("dd/MM/yyyy")),
"completion" -> optional(jodaDate("dd/MM/yyyy")),
"expectedMoveIn" -> optional(jodaDate("dd/MM/yyyy"))
)(RelocationDto.apply)(RelocationDto.unapply)
)
I would like to add validation so that if _type=="sale", then exchange is a required field, but if _type=="let" then expectedMoveIn is a required field. I cant seem to find a way to do this with the standard play validators, is there a way to do it?
Cheers
Nic

Answer 1

I used to work for Her Majesty's Revenue and Customs (UK) and looks like HMRC have open-sourced a very useful and easy to use library specialising in conditional Play mappings: https://github.com/hmrc/play-conditional-form-mapping

Answer 2

You can use the verifying method of Mapping. This will allow you to create constraints after the form has been successfully bound to a class, where you can access other fields. It accepts the error message and a boolean function, which will add an error to the form when false.
val relocationDtoForm: Form[RelocationDto] = Form(
mapping(
"_type" -> text,
"sourceToken" -> text,
"exchange" -> optional(jodaDate("dd/MM/yyyy")),
"completion" -> optional(jodaDate("dd/MM/yyyy")),
"expectedMoveIn" -> optional(jodaDate("dd/MM/yyyy"))
)(RelocationDto.apply)(RelocationDto.unapply)
.verifying(
"Exchange is required for sales.",
relocationRto => if(relocationRto._type == "sale") relocationRto.isDefined else true
).verifying(
"Expected move in is required for let?",
relocationRto => if(relocationRto._type == "let") expectedMoveIn.isDefined else true
)
)

Answer 3

My final solution at long last was:
def save(id: String) = Action { implicit request =>
//Runs some extra validation based on the _type value
def typeSpecificValidate(params: Map[String,Seq[String]]): Seq[FormError] = params("_type") match {
case Seq("sale") => {
Forms.tuple(
"exchange" -> jodaDate("dd/MM/yyyy"),
"completion" -> jodaDate("dd/MM/yyyy")
).bind(params.mapValues(seq => seq.head)) match {
case Left(errors) => errors //Bind returns a Left(List(FormErrors)) or a Right(boundTuple)
case _ => Nil
}
}
case Seq("let") => {
Forms.tuple(
"expectedMoveIn" -> jodaDate("dd/MM/yyyy")
).bind(params.mapValues(seq => seq.head)) match {
case Left(errors) => errors //Bind returns a Left(List(FormErrors)) or a Right(boundTuple)
case _ => Nil
}
}
}
val extraErrors = typeSpecificValidate(request.body.asFormUrlEncoded.get)
Logger.debug("Custom validator found: " + extraErrors)
val ff = relocationDtoForm.bindFromRequest
ff.copy(errors = ff.errors ++ extraErrors).fold(
formWithErrors => {
formWithErrors.errors.foreach(e => Logger.debug(e.toString))
BadRequest(views.html.relocations.detail(id, formWithErrors))
},
relocationDto => {
Logger.debug(relocationDto.toString)
Ok(views.html.relocations.detail(id, relocationDtoForm.fill(relocationDto)))
}
)
}