how to represent nested JSON object in a case class using Json4s?

Question

Given an example JSON object with a nested object who's properties are unkown:

      { "Key":"01234",
          "eventProperties":{
             "unknownProperty1":"value",
             "unknownProperty2":"value",
             "unknownProperty3":"value"
          },
       }

I have tried to use json4s' extract function with the following case class (In Scala):

case class nestedClass(Key:String, eventProperties:Map[(String,Any)])

Which results in the following error:

org.json4s.package$MappingException: Can't find constructor for nestedClass

Is it possible to do this without defining every possible property of eventProperties?

Update: there was a bug in json4s 3.2.10 causing this issue - updating to 3.2.11 and extracting to Map[String,Any] works fine.

Answer 1

I'm not sure what you are doing to get the exception you have posted, but the following works (note a Map instead of List):

import org.json4s._
import org.json4s.jackson.JsonMethods._
import org.json4s.DefaultFormats

val json = parse("""
{ "key":"01234",
  "eventProperties":{
    "unknownProperty1":"value",
    "unknownProperty2":"value",
    "unknownProperty3":"value"
  }
}
""")

case class NestedClass(key:String, eventProperties:Map[String,Any])

implicit val formats = DefaultFormats

json.extract[NestedClass]