return type for findAndModify with futures - scala

Question

Say I'm using an async library to read and write data. If a failure, I get an error message as a string, otherwise the data. Is there a better way to represent the return type than Future[Either[String, Future[Data]]]?
Possible implementation:
def createData(name: String): Future[Either[String, Future[Data]]] = {
dataDAO.findOneByName(name).flatMap {
case Some(data) =>
Future.successful(Left(s"Data with name already exists. $name"))
case None =>
val data = Data.createFromName(name)
dataDAO.save(data).map {
lastError =>
data
}.right.futureSuccessful
}
}

Answer 1

Your return type should be Future[Either[String, Data]]
To archive this you need to change your second case to:
case None =>
val data = Data.createFromName(name)
dataDAO.save(data).map {
_ => Right(data)
}
I even would improve your error type from String to e.g. CreateDataError, so your return type would be Future[Either[CreateDataError, Data]] and your first case would be
// Having somewhere decalred
trait CreateDataError
object DataAlreadyExistsError
//...
//...
case Some(data) =>
Future.successful(Left(DataAlreadyExistsError))