scala.MatchError：轉換為JSON時為null

Question

我有一個基於Play的應用程序！ 框架。 還有下課

package models

sealed trait Role

object Role {

  case object Administrator extends Role
  case object Accountant extends Role
  case object Cashier extends Role
  case object Repairman extends Role

  implicit def Role2Int(role: Role): Int = {
    role match {
      case Administrator => 1
      case Accountant => 2
      case Cashier => 4
      case Repairman => 8
      case _ => throw new NotImplementedError(s"Conversion from $role to Int is not supported yet.")
    }
  }

  implicit def Int2Role(i: Int): Role = {
    i match {
      case 1 => Administrator
      case 2 => Accountant
      case 4 => Cashier
      case 8 => Repairman
      case _ => throw new NotImplementedError(s"Not supported role value.")
    }
  }
}

case class User(
  id: Long,
  lastName: String,
  firstName: String,
  middleName: Option[String],
  role: Role,
  creationDate: Date,
  editDate: Option[Date],
  creatorId: Long,
  editorId: Option[Long]
)

我需要將User類型的實例序列化為JSON。 要使用standart play的json-serializer做到這一點，我必須實現一個writer。

順便說一句：奇怪的是，在如此簡單的情況下，必須寫這么多行代碼才能得到結果（對讀者而言也是一樣）。 可能有更好的解決方案？

好的，作家完成了。 但是當我嘗試序列化時

import java.sql.Date

import models.Role.Accountant
import models._
import play.api.libs.json.{Writes, Json}

implicit val userWrites = new Writes[User] {
  def writes(user: User) = Json.obj(
    "id" -> user.id,
    "lastName" -> user.lastName,
    "firstName" -> user.firstName,
    "middleName" -> user.middleName,
    "role" -> Role.Role2Int(user.role),
    "creationDate" -> user.creationDate,
    "editDate" -> user.editDate,
    "creatorId" -> user.creatorId,
    "editorId" -> user.editorId
  )
}

val user = User(1, "Smith", "John", null, Accountant, new Date(System.nanoTime()), null, 0, null)

Json.toJson(user)

我懂了

scala.MatchError: null
    at play.api.libs.json.DefaultWrites$$anon$7.writes(app.sc2.tmp:180)
    at play.api.libs.json.DefaultWrites$$anon$7.writes(app.sc2.tmp:178)
    at play.api.libs.json.Json$.toJsFieldJsValueWrapper(app.sc2.tmp:139)
    at #worksheet#.$anon$1.writes(app.sc2.tmp:12)
    at #worksheet#.$anon$1.writes(app.sc2.tmp:7)
    at play.api.libs.json.Json$.toJson(app.sc2.tmp:104)
    at #worksheet#.get$$instance$$res1(app.sc2.tmp:25)
    at #worksheet#.#worksheet#(app.sc2.tmp:49)

我做錯了什么？

Answer 1

該行：

val user = User(1, "Smith", "John", null, Accountant, new Date(System.nanoTime()), null, 0, null)

應該：

val user = User(1, "Smith", "John", None, Accountant, new Date(System.nanoTime()), None, 0, None)

如上述評論所述，將null更改為None。