How to transform submitted json in Play 2.0? - scala

Question

I'm trying to build a REST API using play 2.0. I have a User case class that contains some fields (like username & password) that shouldn't be updatable by the updateMember method.
Is there a good, functional way, of dealing with multiple Options somehow, because request.body.asJson returns an Option[JsValue], and my user lookup also returns an Option:
package controllers.api
import org.joda.time.LocalDate
import play.api.Play.current
import play.api.db.slick.{DB, Session}
import play.api.mvc._
import play.api.libs.json._
import play.api.libs.functional.syntax._
import models.{Gender, User, UserId}
import repositories.UserRepository
object Member extends Controller {
def updateMember(id: Long) = Action {
DB.withSession {
implicit session: Session =>
val json: JsValue = request.body.asJson // how to deal with this?
val repository = new UserRepository
repository.findById(new UserId(id)).map {
user =>
def usernameAppender = __.json.update(
__.read[JsObject].map { o => o ++ Json.obj("username" -> user.username) }
)
json.transform(usernameAppender) // transform not found
Ok("updated")
}.getOrElse(NotFound)
}
}
}
I could move the map call to where I try to parse the request, but then inside there I guess I'd need another map over the user Option like I already have. So in that style, I'd need a map per Option.
Is there a better way of dealing with multiple Options like this in FP?

Answer 1

You're basically dealing with a nested monad, and the main tool for working with such is flatMap, particularly if both options being None has the same semantic meaning to your program:
request.body.asJson.flatMap { requestJson =>
val repository = new UserRepository
repository.findById(new UserId(id)).map { user =>
def usernameAppender = __.json.update(
__.read[JsObject].map { o => o ++ Json.obj("username" -> user.username) }
)
requestJson.transform(usernameAppender)
Ok("updated") // EDIT: Do you not want to return the JSON?
}
}.getOrElse(NotFound)
But it might also be the case that your Nones have different meanings, in which case, you probably just want to pattern match, and handle the error cases separately:
request.body.asJson match {
case Some(requestJson) =>
val repository = new UserRepository
repository.findById(new UserId(id)).map { user =>
def usernameAppender = __.json.update(
__.read[JsObject].map { o => o ++ Json.obj("username" -> user.username) }
)
requestJson.transform(usernameAppender)
Ok("updated")
}.getOrElse(NotFound)
case None => BadRequest // Or whatever you response makes sense for this case
}