using enumeratum enum as BSONDocument value does not compile - scala

Question

when I try to wrap my query in BSONDocument and putting my enumeratum enum as the value it docent compile.
for example, my enum:
sealed trait ProcessingStatus extends EnumEntry with UpperSnakecase
object ProcessingStatus extends Enum[ProcessingStatus] with ReactiveMongoBsonEnum[ProcessingStatus] {
val values: IndexedSeq[ProcessingStatus] = findValues
case object Processing extends ProcessingStatus
case object Done extends ProcessingStatus
}
and I have play json serializer that explains how to serialize:
object JsonSerialization {
import reactivemongo.api.bson._
implicit object ProcessingStatusReader extends BSONReader[ProcessingStatus] {
override def readTry(bson: BSONValue): Try[ProcessingStatus] = bson match {
case BSONString(s) => bson.asTry[ProcessingStatus]
case _ => Failure(new RuntimeException("String value expected"))
}
}
implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
}
//Report Serializers
implicit val ProcessingStatusFormat: Format[ProcessingStatus] = EnumFormats.formats(ProcessingStatus)
implicit val ReportFormat: OFormat[Report] = Json.format[Report]
}
and now in my dao this does not compile:
import reactivemongo.play.json.compat.json2bson.{toDocumentReader, toDocumentWriter}
import serializers.JsonSerialization._
def findReport(reportId: String) = {
val test = BSONDocument("123" -> ProcessingStatus.Processing) // dosent compile
}
screenshot:
compilation error:
overloaded method apply with alternatives:
(elms: Iterable[(String, reactivemongo.api.bson.BSONValue)])reactivemongo.api.bson.BSONDocument <and>
(elms: reactivemongo.api.bson.ElementProducer*)reactivemongo.api.bson.BSONDocument
cannot be applied to ((String, enums.ProcessingStatus.Done.type))
val test = BSONDocument("status" -> ProcessingStatus.Done)

Answer 1

An IDE error is not a compilation error (recommend to use sbt and its console to tests).
Your code (simplified as bellow), is compiling fine, whatever is telling the IDE (which is wrong).
import reactivemongo.api.bson._
import scala.util.Try
trait ProcessingStatus {
def entryName = "foo"
}
object JsonSerialization {
implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
}
}
import JsonSerialization._
BSON.write(new ProcessingStatus {})
Note.1: writeTry doesn't override anything, so the modifier is useless (and can lead to missunderstanding).
Note.2: Try(..) with a pure value such as BSONString(t.entryName) is over-engineered, rather use Success(..).
Note.3: Convenient factories are available such as val w = BSONWriter[T] { t => ... }.
Edit:
The typeclass BSONWriter (as most typeclass) is invariant, so having a BSONWriter[T] in the implicit scope doesn't allow to resolve a BSONWriter[U] forSome { U <: T }.
trait ProcessingStatus {
def entryName: String
}
object ProcessingStatus {
case object Done extends ProcessingStatus { val entryName = "done" }
}
object JsonSerialization {
implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
}
}
import JsonSerialization._
BSON.write(ProcessingStatus.Done
/*
<console>:32: error: could not find implicit value for parameter writer: reactivemongo.api.bson.BSONWriter[ProcessingStatus.Done.type]
BSON.write(ProcessingStatus.Done)
*/
// --- BUT ---
BSON.write(ProcessingStatus.Done: ProcessingStatus)
// Success(BSONString(done))
Also exposing Done (and other cases) as ProcessingStatus in the API is working.
import reactivemongo.api.bson._
import scala.util.Try
sealed trait ProcessingStatus {
def entryName: String
}
object ProcessingStatus {
val Done: ProcessingStatus = new ProcessingStatus { val entryName = "done" }
}
object JsonSerialization {
implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
}
}
import JsonSerialization._
BSON.write(ProcessingStatus.Done)