Scala serialization exception with Enumeration Value - mongodb

Question

I'm using the play 2.1 framework for scala and the MongoDB Salat plugin.
When I update an Enumeration.Value I got an exception:
java.lang.IllegalArgumentException: can't serialize class scala.Enumeration$Val
at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:270) ~[mongo-java-driver-2.11.1.jar:na]
at org.bson.BasicBSONEncoder.putIterable(BasicBSONEncoder.java:295) ~[mongo-java-driver-2.11.1.jar:na]
at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:234) ~[mongo-java-driver-2.11.1.jar:na]
at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:174) ~[mongo-java-driver-2.11.1.jar:na]
at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:120) ~[mongo-java-driver-2.11.1.jar:na]
at com.mongodb.DefaultDBEncoder.writeObject(DefaultDBEncoder.java:27) ~[mongo-java-driver-2.11.1.jar:na]
Inserting the Enumeration.Value works fine. My case class looks like:
case class User(
#Key("_id") id: ObjectId = new ObjectId,
username: String,
email: String,
#EnumAs language: Language.Value = Language.DE,
balance: Double,
added: Date = new Date)
and my update code:
object UserDAO extends ModelCompanion[User, ObjectId] {
val dao = new SalatDAO[User, ObjectId](collection = mongoCollection("users")) {}
def update(): WriteResult = {
UserDAO.dao.update(q = MongoDBObject("_id" -> new ObjectId(id)), o = MongoDBObject("$set" -> MongoDBObject("language" -> Language.EN))))
}
}
Any ideas how to get that working?
EDIT:
workaround: it works if I cast the Enumeration.Value toString, but that's not how it should be...
UserDAO.dao.update(q = MongoDBObject("_id" -> new ObjectId(id)), o = MongoDBObject("$set" -> MongoDBObject("language" -> Language.EN.toString))))

Answer 1

It is possible to add a BSON encoding for Enumeration. So, the conversion is done in a transparent manner.
Here is the code
RegisterConversionHelpers()
custom()
def custom() {
val transformer = new Transformer {
def transform(o: AnyRef): AnyRef = o match {
case e: Enumeration$Val => e.toString
case _ => o
}
}
BSON.addEncodingHook(classOf[Enumeration$Val], transformer)
}
}

Answer 2

At the time of writing mongoDB doesn't place nice with scala enums, I use a decorator method as a work around.
Say you have this enum:
object EmployeeType extends Enumeration {
type EmployeeType = Value
val Manager, Worker = Value
}
and this mongodb record:
import EmployeeType._
case class Employee(
id: ObjectId = new ObjectId
)
In your mongoDB, store the integer index of the enum instead of the enum itself:
case class Employee(
id: ObjectId = new ObjectId,
employeeTypeIndex: Integer = 0
){
def employeeType = EmployeeType(employeeTypeIndex); /* getter */
def employeeType_=(v : EmployeeType ) = { employeeTypeIndex= v.id} /* setter */
}
The extra methods implement getters and setters for the employee type enum.

Answer 3

Salat only does its work when you serialize to and from your model object with the grater, not when you do queries with MongoDB-objects yourself. The mongo driver api knows nothing about the annotation #EnumAs. (In addition to that even if you could use salat for that, how would it be able to know that you are referring to User.language in a generic key->value MongoDBObject?)
So you have to do like you describe in your workaround. Provide the "value" of the enum yourself when you want to do queries.