Play: How to transform JSON while writing/reading it to/from MongoDB

JsonExtensions

I usually have a JsExtensions object in my application which looks like the following :

import reactivemongo.bson.BSONObjectIDobject JsonExtensions {  import play.api.libs.json._  def withDefault[A](key: String, default: A)(implicit writes: Writes[A]) = __.json.update((__ \ key).json.copyFrom((__ \ key).json.pick orElse Reads.pure(Json.toJson(default))))  def copyKey(fromPath: JsPath,toPath:JsPath ) = __.json.update(toPath.json.copyFrom(fromPath.json.pick))  def copyOptKey(fromPath: JsPath,toPath:JsPath ) = __.json.update(toPath.json.copyFrom(fromPath.json.pick orElse Reads.pure(JsNull)))  def moveKey(fromPath:JsPath, toPath:JsPath) =(json:JsValue)=> json.transform(copyKey(fromPath,toPath) andThen fromPath.json.prune).get}

For a simple model

case class SOUser(name:String,_id:BSONObjectID)

you can write your json serializer/deserializer like this:

object SOUser{  import play.api.libs.json.Format  import play.api.libs.json.Json  import play.modules.reactivemongo.json.BSONFormats._  implicit val soUserFormat= new Format[SOUser]{    import play.api.libs.json.{JsPath, JsResult, JsValue}    import JsonExtensions._    val base = Json.format[SOUser]    private val publicIdPath: JsPath = JsPath \ 'id    private val privateIdPath: JsPath = JsPath \ '_id \ '$oid    def reads(json: JsValue): JsResult[SOUser] = base.compose(copyKey(publicIdPath, privateIdPath)).reads(json)    def writes(o: SOUser): JsValue = base.transform(moveKey(privateIdPath,publicIdPath)).writes(o)  }}

here is what you get in the console :

scala> import reactivemongo.bson.BSONObjectIDimport reactivemongo.bson.BSONObjectIDscala> import models.SOUserimport models.SOUserscala> import play.api.libs.json.Jsonimport play.api.libs.json.Jsonscala>scala> val user = SOUser("John Smith", BSONObjectID.generate)user: models.SOUser = SOUser(John Smith,BSONObjectID("52d00fd5c912c061007a28d1"))scala> val jsonUser=Json.toJson(user)jsonUser: play.api.libs.json.JsValue = {"name":"John Smith","id":"52d00fd5c912c061007a28d1","_id":{}}scala> Json.prettyPrint(jsonUser)res0: String ={  "name" : "John Smith",  "id" : "52d00fd5c912c061007a28d1",  "_id" : { }}scala> jsonUser.validate[SOUser]res1: play.api.libs.json.JsResult[models.SOUser] = JsSuccess(SOUser(John Smith,BSONObjectID("52d00fd5c912c061007a28d1")),/id)

Applying this to your example

val _personReads: Reads[JsObject] = (  (__ \ 'id).read[String] ~  (__ \ 'name).read[String] ~  (__ \ 'surname).read[String]).reduce

Doesn't compile by default, I guess you meant to write :

val _personReads: Reads[(String,String,String)] = (  (__ \ 'id).read[String] ~  (__ \ 'name).read[String] ~  (__ \ 'surname).read[String]).tupled

in which case you can do the following

import play.api.libs.json._import play.api.libs.json.Reads._import play.api.libs.functional.syntax._import play.modules.reactivemongo.json.BSONFormats._import reactivemongo.bson.BSONObjectIDdef copyKey(fromPath: JsPath,toPath:JsPath ) = __.json.update(toPath.json.copyFrom(fromPath.json.pick))val json = """{  "id": "ff59ab34cc59ff59ab34cc59",  "name": "Joe",  "surname": "Cocker"}"""val originaljson = Json.parse(json)val publicIdPath: JsPath = JsPath \ 'idval privateIdPath: JsPath = JsPath \ '_id \ '$oidval _personReads: Reads[(BSONObjectID,String,String)] = (  (__ \ '_id).read[BSONObjectID] ~  (__ \ 'name).read[String] ~  (__ \ 'surname).read[String]).tupledval personReads=_personReads.compose(copyKey(publicIdPath,privateIdPath))originaljson.validate(personReads)// yields res5: play.api.libs.json.JsResult[(reactivemongo.bson.BSONObjectID, String, String)] = JsSuccess((BSONObjectID("ff59ab34cc59ff59ab34cc59"),Joe,Cocker),/id)

or you meant that you want to move the value of the id key to _id \ $oid which can be accomplished with

import play.api.libs.json._import play.api.libs.json.Reads._import play.api.libs.functional.syntax._import play.modules.reactivemongo.json.BSONFormats._import reactivemongo.bson.BSONObjectIDdef copyKey(fromPath: JsPath,toPath:JsPath ) = __.json.update(toPath.json.copyFrom(fromPath.json.pick))val json = """{  "id": "ff59ab34cc59ff59ab34cc59",  "name": "Joe",  "surname": "Cocker"}"""val originaljson = Json.parse(json)val publicIdPath: JsPath = JsPath \ 'idval privateIdPath: JsPath = JsPath \ '_id \ '$oidoriginaljson.transform(copyKey(publicIdPath,privateIdPath) andThen publicIdPath.json.prune)

You can't have a BSONObjectID in there for now since you are manipulating object from the JsValue type hierarchy. When you pass json to reactivemongo it is converted to a BSONValue. A JsObject will be converted to a BSONDocument. if the JsObject contains a path for _id\$oid this path will be converted to a BSONObjectId automatically and it will be stored as an ObjectID in mongodb.

The original question is really about reactivemongo's (sgodbillon et al) treatment of the native mongodb _id. The chosen answer is instructive and correct but obliquely addresses the OP's concern whether "it will all just work".

Thanks to https://github.com/ReactiveMongo/ReactiveMongo-Play-Json/blob/e67e507ecf2be48cc71e429919f7642ea421642c/src/main/scala/package.scala#L241-L255, I believe it will.

import scala.concurrent.Awaitimport scala.concurrent.duration.Durationimport play.api.libs.concurrent.Execution.Implicits.defaultContextimport play.api.libs.functional.syntax._import play.api.libs.json._import play.modules.reactivemongo.json.collection.JSONCollectionimport reactivemongo.api._import reactivemongo.bson.BSONObjectIDimport reactivemongo.play.json._case class Person(id: BSONObjectID,name: String,surname: String)implicit val PersonFormat: OFormat[Person] = (  (__ \ "_id").format[BSONObjectID] and    (__ \ "name").format[String] and    (__ \ "surname").format[String])(Person.apply, unlift(Person.unapply))val driver = new reactivemongo.api.MongoDriverval connection = driver.connection(List("localhost"))val db = connection.db("test")val coll = db.collection[JSONCollection]("persons")coll.drop(false)val id = BSONObjectID.generate()Await.ready(coll.insert(Person(id, "Joe", "Cocker")), Duration.Inf)Await.ready(coll.find(Json.obj()).one[Person] map { op => assert(op.get.id == id, {}) }, Duration.Inf)

The above is a minimal working example of your case class using id and the database storing it as _id. Both are instantiated as 12-byte BSONObjectIDs.