How to dynamically select class type when parsing JSON to object in Play Framework? - scala

Question

The following sample code uses Play Framework to parse JSON to an object:
def createEvent(): Action[JsValue] = Action.async(parse.tolerantJson) {
request => {
request.body.validate[SomeEvent] match {
case o:JsSuccess[SomeEvent] => {
//do something
Future(Created)
}
}
}
}
Is it possible to generalise it so it can handle different event types? e.g.
def createEvent(): Action[JsValue] = Action.async(parse.tolerantJson) {
request => {
val eventType = request.contentType match {
case Some("SomeEventType") => SomeEvent
case Some("OtherEventType") => OtherEvent
}
request.body.validate[eventType] match {
case o:JsSuccess[eventType] => {
//do something
Future(Created)
}
}
}
}
Currently, the above code will fail in the line request.body.validate[eventType]

Answer 1

You can extract body.validate[T] into a function and call it from your patten matching construct with a proper type, i.e:
def extract[T: JsonFormat](implicit req: Request[AnyContent]) = req.body.valudate[T]
request.contentType match {
case Some("SomeEventType") => extract[SomeEvent]
case Some("OtherEventType") => extract[OtherEvent]
}

Answer 2

You can read and create class from contentType dynamically. But you can have problem, if will be no implicit Format for extracted type in scope:
error: No Json formatter found for type A. Try to implement an implicit Format for this type.
or
java.lang.ClassNotFoundException: models.Bazz
The available data:
model
package models
case class Bar(name: String)
request
request.contentType: Option[String] = Some("models.Bar")
incoming body
request.body: JsValue = """{"name": "bar name"}"""
format[Bar]
implicit val BarFormat = Json.format[models.Bar]
extractor:
def extract[A <: Any](ct: String, json: JsValue)(implicit format: Format[A]) = {
val manifest:Manifest[A] = Manifest.classType[A](Class.forName(ct))
json.validate[A]
}
request.contentType.map(extract(_, request.body))
res1: Option[play.api.libs.json.JsResult[models.Bar]] = Some(JsSuccess(Bar(bar name),/name))
you can see https://github.com/strongtyped/fun-cqrs/blob/demos/shop-sample/samples/shop/src/main/scala/funcqrs/json/TypedJson.scala for other way of deserializing self-contained json.