Options for serializing enumerations

[devth]

Is there any way to config how an enumeration is serialized?

I'm seeing:

{
  enumClass: "com.website.model.Comparison",
  value: "Newer"
}

but I'd rather just see

"Newer"

[christophercurrie]

Haven't done any specific work on Enumerations yet. When I'm next able, I'll take a look and see what can be done.

[christophercurrie]

This one is tricky. The JVM type of every value of every Enumeration is the same, so there's no way I can deduce the Scala type of the Enumeration based on the Class<?>. This is why the serialization looks the way it does; to give the deserializer something to work with.

I might be able to devise an annotation that you can add to either the type or the getter for a given member. The solution is not ideal, because it's complicated by the fact that Scala does not currently provide a compile-time accessor to the class for a "singleton object". See SI-2453.

Given that the only choice is String annotation values, the user interface would look something like:

package sample

// annotate the type directly, so jackson-module-scala always knows how to handle it.
@JsonScalaEnum("sample.Weekday")
object Weekday extends Enumeration {
  type Weekday = Value
  val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
}

Or, in the case of the Enumeration being from a third-party (i.e., unmodifiable) library:

import sample.Weekday._
import scala.reflect.BeanProperty

class EnumHolder {

  @BeanProperty // tell scala to generate setter/getter
  @JsonScalaEnum("sample.Weekday") // tell jackson-module-scala the parent enum object
  var day: Weekday

}

The last piece to specify is what the behavior should be in the case of a missing annotation. I'm not really a fan of the current behavior, but there might be folks out there using it, so I'll probably retain it as a fallback for the 1.9.x series, but deprecated somehow. Unless there is vocal opposition I'll probably drop the fallback in favor of an exception.

[hvesalai]

Have a look at Lift JSON, it has the https://github.com/lift/lift/blob/master/framework/lift-base/lift-json-ext/src/main/scala/net/liftweb/json/ext/EnumSerializer.scala that is instantiated with the type of Enumeration that is expected.

edit: my previous comment was wrong. Lift json uses a Format that is given the type of Enumeration to deserialize

[slorber]

+1 it would be nice to have that.
I'm considering leaving jackson because of that.

[christophercurrie]

I've just pushed code to master to try and address this, and am developing documentation for it in the wiki:

https://github.com/FasterXML/jackson-module-scala/wiki/Enumerations

Feedback is welcome; the feature should be available in tonight's nightly build.

[christophercurrie]

The above annotation support went out in the 2.2 release. Feel free to open a new issue if there are problems with the new feature.