spray-json recursive json issue - could not find implicit value for evidence parameter

Question

Hello I am bit struggling with parsing a json with spray-json libary whith recursive data structure.

I have following case class structure and Protocol defined

import spray.json.DefaultJsonProtocol
import spray.json._

case class OfferAnalysisReport(BUG: DleTN, DOM: DleTN) extends AnalyticalReport
case class DleTN(doc_count: Int, result: AggsDefinition)
case class BucketDefinition(key: String, doc_count: Int, result: Option[AggsDefinition])
case class AggsDefinition(buckets: List[BucketDefinition])

object OfferAnalysisReportProtocol extends DefaultJsonProtocol {
  implicit val aggsDefFormat = lazyFormat(jsonFormat(AggsDefinition,"buckets"))

  implicit val bucketDefinitionFormat = lazyFormat(jsonFormat(BucketDefinition,"key","doc_count","result"))

  implicit val dleTypNemovitostisFormat = jsonFormat2(DleTypuNemovitosti)

  implicit val OfferAnalysisReportFormat = jsonFormat2(OfferAnalysisReport)
}

In the test I am importing:

import spray.json._
import OfferAnalysisReportProtocol._

But I am still getting

Error: couldn't find implicit value for evidence parameter of type BuckedDefinition.

Am I missing something important here? Could someone give me a hint?

Answer 1

You will have to wrap your format constructor with lazyFormat as you have done, but you also have to supply an explicit type annotation like this:

implicit val fooFormat: JsonFormat[Foo] = lazyFormat(jsonFormat(Foo, "i", "foo"))

Source: https://github.com/spray/spray-json#jsonformats-for-recursive-types