Jackson scala module: deserialize case object enumeration - json

Question

I am using Jackson scala module and I need to serialize/deserialize case object enumerations. The serialization works fine, but when deserializing back the values I get a com.fasterxml.jackson.databind.exc.InvalidDefinitionException. There is a way to make it work? I would like to avoid using "classic" scala enumerations, since I would lose the ability to define enumeration hierarchies.
Code used for the tests:
import com.fasterxml.jackson.annotation.JsonValue
import com.fasterxml.jackson.databind.{DeserializationFeature, ObjectMapper}
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper
sealed trait Operations { #JsonValue def jsonValue: String }
case object Foo extends Operations { override def jsonValue: String = "Foo" }
case object Bar extends Operations { override def jsonValue: String = "Bar" }
sealed trait RichOperations extends Operations
case object Baz extends RichOperations { override def jsonValue: String = "Baz" }
object JsonUtils extends App {
val jsonMapper = new ObjectMapper() with ScalaObjectMapper
jsonMapper.registerModule(DefaultScalaModule)
.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
def toJson(value: Any): String = jsonMapper.writeValueAsString(value)
def fromJson[T: Manifest](json: String): T = jsonMapper.readValue[T](json)
println(toJson(Foo)) // "Foo"
println(toJson(Bar)) // "Bar"
println(toJson(Baz)) // "Baz"
println(fromJson[Operations](toJson(Foo))) // throws InvalidDefinitionException
println(fromJson[Operations](toJson(Bar)))
println(fromJson[RichOperations](toJson(Baz)))
}

Answer 1

I solved the problem defining custom deserializers.
import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.databind.{DeserializationContext, JsonDeserializer}
class OperationsDeserializer extends JsonDeserializer[Operations] {
override def deserialize(p: JsonParser, ctxt: DeserializationContext): Operations = {
p.getValueAsString match {
case Foo.jsonValue => Foo
case Bar.jsonValue => Bar
case value => throw new IllegalArgumentException(s"Undefined deserializer for value: $value")
}
}
}
class RichOperationsDeserializer extends JsonDeserializer[Operations] {
override def deserialize(p: JsonParser, ctxt: DeserializationContext): Operations = {
p.getValueAsString match {
case Foo.jsonValue => Foo
case Bar.jsonValue => Bar
case Baz.jsonValue => Baz
case value => throw new IllegalArgumentException(s"Undefined deserializer for value: $value")
}
}
}
Moreover, since stable identifiers are required in match/case, I changed jsonValue from def to val: this unfortunately requires the declaration of #JsonValue annotation in each case object enumeration.
import com.fasterxml.jackson.databind.annotation.JsonDeserialize
#JsonDeserialize(using = classOf[OperationsDeserializer])
sealed trait Operations { val jsonValue: String }
case object Foo extends Operations { #JsonValue override val jsonValue: String = "Foo" }
case object Bar extends Operations { #JsonValue override val jsonValue: String = "Bar" }
#JsonDeserialize(using = classOf[RichOperationsDeserializer])
sealed trait RichOperations extends Operations
case object Baz extends RichOperations { #JsonValue override val jsonValue: String = "Baz" }