找不到类型为play.api.libs.json.JsValue的Json序列化程序作为JsObject

Question

I'm trying to migrate my project from using play2-reactivemongo version 0.10.5.0.akka23 to using version 0.11.7.play23 . I've already added the following import to fix the problems addressed in this question :

import play.modules.reactivemongo.json._

With the former version, the following code worked:

val updateEntity = Json.obj("_id" -> Json.obj("$oid" -> id))
val entity = Json.parse(stringJson)
collection.update(updateEntity, entity)

however, using the new version, the third line gives a compile error:

[error] No Json serializer as JsObject found for type play.api.libs.json.JsValue. Try to implement an implicit OWrites or OFormat for this type.
[error]     collection.update(updateEntity, entity)
[error]                      ^

I've tried introducing an implicit OWriter :

implicit val toJsObject: OWrites[JsValue] = OWrites.apply(_.as[JsObject])

but that gives an implicit declaration conflict:

[error] ambiguous implicit values:
[error]  both value toJsObject of type play.api.libs.json.OWrites[play.api.libs.json.JsValue]
[error]  and object JsObjectDocumentWriter in trait ImplicitBSONHandlers of type play.modules.reactivemongo.json.JsObjectDocumentWriter.type
[error]  match expected type collection.pack.Writer[play.api.libs.json.JsObject]
[error]     collection.update(updateEntity, entity)
[error]                      ^

changing the second line to

val entity = Json.parse(stringJson).as[JsObject]

fixes the problem, but I have a lot of these around my code and I was hoping for a simpler solution.

Answer 1

Just got bit by this too. The trick is to remove

import play.modules.reactivemongo.json._

and instead use

import reactivemongo.play.json._

The play.modules version doesn't provide the identity OWriter.