How to refactor this scala code? - scala

Question

I want to refactor this code into something more readable and better in general. I know that in Scala there are normally neat ways of doing things but for me it's getting a bit messy (BTW I'm using the Play library in the code). this is a snippet of my code:
class HomeController #Inject()
(cc: ControllerComponents)
(implicit val config: Configuration)
extends AbstractController(cc) {
def removeIdElement(uid: String) =
HAction(uid, "AuthEvent", 1, "login", parse.text).async {
implicit request: Request[String] =>
val promise = Promise[Result]()
Future {
val removeId = request.body.toLong
println(s"remove id $removeId")
promise completeWith {
idElementsDAO.remove(removeId, uid.toLong) map {
_ => Ok("")
} recover {
case t: Throwable =>
val errorMessage: String = getMessageFromThrowable(t)
println("remove id element failure " + errorMessage)
BadRequest(errorMessage)
}
}
} recover {
case t: Throwable =>
val errorMessage: String = getMessageFromThrowable(t)
println("remove id element failure " + errorMessage)
promise.success(BadRequest(errorMessage))
}
promise.future
}
}

Answer 1

Assuming that idElementsDAO.remove return a Future, this is probably more idiomatic:
def removeIdElement(uid: String) =
HAction(uid, "AuthEvent", 1, "login", parse.text).async {implicit request =>
val removeId = request.body.toLong
println(s"remove id $removeId")
idElementsDAO.remove(removeId, uid.toLong)
.map(_ => NoContent) // probably more correct than `Ok("")`
.recover {
case t: Throwable =>
val errorMessage: String = getMessageFromThrowable(t)
println("remove id element failure " + errorMessage)
BadRequest(errorMessage)
}
}
No need for the Promise or the call to Future {...} (Future.apply).
Keep in mind, it's probably not the best idea to directly pass the underlying error of any Throwable directly to the http client (browser?).
If you add generic error handling code to the global error handler (for unexpected errors) that logs the error and sends a generic message to the front-end, you can then write it even cleaner like this:
def removeIdElement(uid: String) =
HAction(uid, "AuthEvent", 1, "login", parse.text).async {implicit request =>
val removeId = request.body.toLong
println(s"remove id $removeId")
for {
_ <- idElementsDAO.remove(removeId, uid.toLong)
} yield NoContent
}
https://www.playframework.com/documentation/2.6.x/ScalaErrorHandling

Answer 2

Here is a simpler version of your code:
class HomeController #Inject()(cc: ControllerComponents)(implicit val config: Configuration)
extends AbstractController(cc) {
def removeIdElement(uid: String) = HAction(uid, "AuthEvent", 1, "login", parse.text).async {
implicit request: Request[String] =>
Future {
val removeId = request.body.toLong
println(s"Removing id $removeId")
removeId
}.flatMap(id => idElementsDAO.remove(id, uid.toLong))
.map(_ => Ok(""))
.recover {
case t: Throwable =>
val errorMessage = getMessageFromThrowable(t)
println(s"Removing id element failed: ${errorMessage}")
BadRequest(errorMessage)
}
}
}
In the above code, a Promise is not needed, and the recover combinator is not repeated.