JSON serializer for ADT do not allows to compile

[Kilic Ali-Firat]

Hi guys, 

These last days, I met a problem that I cannot solve. I design the following logical model using ADT :

Record := CRecord | NRecord

A CRecord and NRecord share common properties so I decided to implement like this : 

  sealed trait BiosRecord {
    val key : String
    val patientId : String
    val startime : Long // in microseconds
    val endtime : Long // in microseconds
    val byteEncoding : Int // 1, 2, 3 or 4
  }

 

case class CBiosRecord
    (
      key : String,
      patientId : String,
      startime : Long, // in microseconds
      endtime : Long, // in microseconds
      byteEncoding : Int, // 1, 2, 3 or 4
    ) extends BiosRecord

case class NBiosRecord
    (
      key : String,
      patientId : String,
      startime : Long, // in microseconds
      endtime : Long, // in microseconds
      byteEncoding : Int, // 1, 2, 3 or 4
      channels : List[NNBiosChannel],
      events : Option[List[NNBiosEvent]],
      preRecordComment : String,
      postRecordComment : String,
    ) extends BiosRecord

Then, I code the JSON reader & writer :

/

******* BiosRecord reads/writes ******/
  implicit val biosRecordReads = {
    val ccwBiosRecord = Json.reads[CCWBiosRecord]
    val nnBiosRecord = Json.reads[NNBiosRecord]
    __.read[CCWBiosRecord](ccwBiosRecord).map(x => x : BiosRecord) |
    __.read[NNBiosRecord](nnBiosRecord).map(x => x : BiosRecord)
  }


  implicit val biosRecordWrites = Writes[BiosRecord] {
    case ccwBiosRecord : CCWBiosRecord =>
      Json.writes[CCWBiosRecord].writes(ccwBiosRecord)
    case nnBiosRecord : NNBiosRecord =>
      Json.writes[NNBiosRecord].writes(nnBiosRecord)
  }


So this code compile and I can also serialize a CRecord to JSON (also the case for a NRecord). Now, I put the lines code giving to me an error :


// ReactiveMongo
import play.modules.reactivemongo.ReactiveMongoApi
import play.modules.reactivemongo.json._, ImplicitBSONHandlers._
import reactivemongo.play.json.collection.{JSONCollection, JsCursor}


// Scala

import scala.concurrent.ExecutionContext.Implicits.global




object MongoDBService {


  val config = Play.application().configuration()
  val mongoCollectionName = config.getString("mongodb.collection.name")
  def reactiveMongoApi = current.injector.instanceOf[ReactiveMongoApi]
  val mongoCollection = reactiveMongoApi.db.collection[JSONCollection](mongoCollectionName)


  def updateBiosChannel
    (
      recordKey : String
    ) : Unit = {

    val futureRecord  = mongoCollection.find(Json.obj("key"->recordKey)).one[BiosRecord]
    futureRecord map { recordOpt =>
      recordOpt match {
        case None => ()
        case Some(record : BiosRecord) =>
 
          record match {
            case cRecord : CBiosRecord =>
              mongoCollection.update(Json.obj("key"->recordKey), ccwRecord)
            case nRecord : NBiosRecord =>
              mongoCollection.update(Json.obj("key"->recordKey), nnRecord)
          }
      }
    }
  }
}

What I'm getting as error => 

app/services/MongoDBService.scala:33: No Json serializer as JsObject found for type play.api.libs.json.JsObject. Try to implement an implicit OWrites or OFormat for this type.
[error]     val futureRecord  = mongoCollection.find(Json.obj("key"->recordKey)).one[BiosRecord]

I really didn't understand this error because I can serialize a BiosRecord to JSON. Is it because I'm using an ADT to make my models or something else ? 

Thanking you in advance, Ali-Firat. 

[Cédric Chantepie]

First fix the missing serializer for JsObject: http://reactivemongo.org/releases/0.11/documentation/json/overview.html

P.S. Please check the formatting of your code. For now it's quite hard to read there.

[Kilic Ali-Firat]

Le mardi 19 juillet 2016 19:28:49 UTC+2, Cédric Chantepie a écrit :

First fix the missing serializer for JsObject: http://reactivemongo.org/releases/0.11/documentation/json/overview.html

When you said "Fix the missing serializer", you means to add the following import : 

import play.api.libs.json.JsObject

Because it's not working too. 

[Cédric Chantepie]

You are missing the import which is required for the JSON support for ReactiveMongo. Please first read the documentation: http://reactivemongo.org/releases/0.11/documentation/json/overview.html

[Kilic Ali-Firat]

Hi Cedric, after reading the document, I have now the following imports: 

import play.modules.reactivemongo.ReactiveMongoApi
import play.api.libs.json._
import play.modules.reactivemongo.json._, ImplicitBSONHandlers._
import reactivemongo.play.json._ // from the reactivemongo doc
import reactivemongo.play.json.collection.JSONCollection

But I still have the following error :

 No Json serializer as JsObject found for type play.api.libs.json.JsObject. Try to implement an implicit OWrites or OFormat for this type.
[error]     val futureRecord  = mongoCollection.find(Json.obj("key"->recordKey)).one[BiosRecord]

[Kilic Ali-Firat]

Hi Cedric,

It works now. 

I removed the two followings import :

// import play.modules.reactivemongo.json._
// import play.modules.reactivemongo.json.collection._

Thank you for the help !

[Cédric Chantepie]

As indicated in the doc, the import for the JSON pack is: import reactivemongo.play.json._