Extract Options from potentially null JSON values using for expression

Question

I have a JSON document where some values can be null. Using for expressions in json4s, how I can yield None, instead of nothing?

The following will fail to yield whe

Answer 1

scala> object OptExtractors {
     |
     |   // Define a custom extractor for using in for-comprehension.
     |   // It returns Some[Option[Double]], instead of Option[Double].
     |   object JDoubleOpt {
     |     def unapply(e: Any) = e match {
     |       case d: JDouble => Some(JDouble.unapply(d))
     |       case _ => Some(None)
     |     }
     |   }
     | }
defined object OptExtractors

scala>

scala> val j = parse("""{
     |   "FormattedID" : "the id",
     |   "PlanEstimate" : null
     | }""")
j: org.json4s.JValue = JObject(List((FormattedID,JString(the id)), (PlanEstimate,JNull)))

scala>

scala> import OptExtractors._
import OptExtractors._

scala>

scala> for {
     |   JObject(list) <- j
     |   JField("FormattedID", JString(id)) <- list
     |   JField("PlanEstimate", JDoubleOpt(points)) <- list
     | } yield (id, points)
res1: List[(String, Option[Double])] = List((the id,None))