斯卡拉/播放2.4 JSON格式問題

Question

我有以下類（簡化的比特存在），這將延長JSON格式，對於表示數據庫級與所述ID字段的特定對象：

import play.api.libs.json._ 
import play.api.libs.functional.syntax._ 

class EntityFormat[T <: Entity](entityFormatter: Format[T]) extends Format[T] { 
    val extendedFormat: Format[T] = (
     __.format[T](entityFormatter) ~ 
    (__ \ "id").format[Option[Long]] 
)(tupleToEntity, entityToTuple) 

    private def tupleToEntity(e: T, id: Option[Long]) = { 
    e.id = id 
    e 
    } 

    private def entityToTuple(e: T) = (e, e.id) 

    def writes(o: T): JsValue = extendedFormat.writes(o) 

    def reads(json: JsValue): JsResult[T] = extendedFormat.reads(json) 
} 

abstract class Entity { 
    var id: Option[Long] = None 
} 

隨着播放2.3，然後我可以寫

implicit val userFormat: Format[User] = new EntityFormat(Json.format[User]) 

然後，這將與生成的JSON中的ID字段一起使用。然而，隨着播放2.4我得到以下編譯時間問題：

No Json formatter found for type Option[Long]. Try to implement an implicit Format for this type. (__ \ "id").format[Option[Long]] 
missing arguments for method tupleToEntity in class DomainEntityFormat; follow this method with `_' if you want to treat it as a partially applied function)(tupleToEntity, entityToTuple) 
                                          ^
missing arguments for method tupleToEntity in class DomainEntityFormat; follow this method with `_' if you want to treat it as a partially applied function)(tupleToEntity, entityToTuple) 
                                              ^

，你應該怎麼做與遊戲2.4延伸到做出那種JSON格式的工作？

Answer 1

相反的：

(__ \ "id").format[Option[Long]] 

嘗試：

(__ \ "id").formatNullable[Long]