Preserve null values in array of Play framework form mapping - arrays

Question

I'm trying to get an idea how can I force Play Scala framework form mapper to save null values in array property.
Example. Request body (print out of snippet below):
AnyContentAsJson({
"entities":["ENI","GDF Suez","Procter & Gamble"],
"entityValues":[null,"42",null]
})
Resulting value of entityValues property after binding:
List(Some(42.0))
But I want to see:
List(None, Some(42.0), None)
Code snippet of controller:
def actionX = Action {implicit request =>
println(request.body)
TaskForm.form.bindFromRequest.fold(
formWithErrors => {
BadRequest("error")
},
taskData => {
println(taskData.entityValues)
}
)
}
Form class with mapping:
case class TaskForm(entities: List[String],
entityValues: List[Option[Double]]) { }
object TaskForm {
val map = mapping(
"entities" -> list(text),
"entityValues" -> list(optional(of(doubleFormat)))
)(TaskForm.apply)(TaskForm.unapply)
val form = Form(
map
)
}
I also tried some combinations of optional and default mapping parameters, but a result is still the same.
Using 0 or any another numeric value instead of null is not a case.
Does anyone have any ideas how to implement such form behaviour?
Thanks in advance for your time and attention.

Answer 1

It looks like you're sending JSON to a form endpoint. While this will work for simple JSON structures, you get no control over how it is done and hence get problems like the one you're seeing.
I'd be explicit about being a JSON-endpoint, and then you can define your own Reads[Option[Double]] that works precisely how you want it to:
First, define the implicits at the Controller level; here's where we get to control the null-handling; it ends up being pretty easy:
implicit val optionalDoubleReads = new Reads[Option[Double]] {
def reads(json: JsValue) = json match {
case JsNumber(n) => JsSuccess(Some(n.toDouble))
case JsString(n) => JsSuccess(Some(n.toDouble))
case JsNull => JsSuccess(None) // The important one
case _ => JsError("error.expected.jsnumber")
}
}
implicit val taskReads = Json.reads[TaskForm]
With that done, we modify your Action to require JSON (using parse.json). The function itself remains remarkably similar to the original form-binding fold:
def actionX = Action(parse.json) { implicit request =>
println(request.body)
request.body.validate[TaskForm].fold(
jsonErrors => {
BadRequest(s"Error: $jsonErrors")
},
taskData => {
println(taskData.entityValues)
Ok(taskData.entityValues.toString)
}
)
}