使用 enumeratum 枚举作为 BSONDocument 值无法编译

Question

当我尝试将我的查询包装在 BSONDocument 中并将我的 enumeratum 枚举作为它解说编译的值时。

例如，我的枚举：

sealed trait ProcessingStatus extends EnumEntry with UpperSnakecase

object ProcessingStatus extends Enum[ProcessingStatus] with ReactiveMongoBsonEnum[ProcessingStatus] {

  val values: IndexedSeq[ProcessingStatus] = findValues

  case object Processing extends ProcessingStatus

  case object Done extends ProcessingStatus

}

我玩了解释如何序列化的 json 序列化程序：

object JsonSerialization {

  import reactivemongo.api.bson._

  implicit object ProcessingStatusReader extends BSONReader[ProcessingStatus] {
    override def readTry(bson: BSONValue): Try[ProcessingStatus] = bson match {
      case BSONString(s) => bson.asTry[ProcessingStatus]
      case _ => Failure(new RuntimeException("String value expected"))
    }
  }

  implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
    override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
  }
  //Report Serializers
  implicit val ProcessingStatusFormat: Format[ProcessingStatus] = EnumFormats.formats(ProcessingStatus)
  implicit val ReportFormat: OFormat[Report] = Json.format[Report]
}

现在在我的 dao 中无法编译：

import reactivemongo.play.json.compat.json2bson.{toDocumentReader, toDocumentWriter}
import serializers.JsonSerialization._

    def findReport(reportId: String) = {
      val test = BSONDocument("123" -> ProcessingStatus.Processing) // dosent compile
    }

截图：

编译错误：

overloaded method apply with alternatives:
  (elms: Iterable[(String, reactivemongo.api.bson.BSONValue)])reactivemongo.api.bson.BSONDocument <and>
  (elms: reactivemongo.api.bson.ElementProducer*)reactivemongo.api.bson.BSONDocument
 cannot be applied to ((String, enums.ProcessingStatus.Done.type))
    val test = BSONDocument("status" -> ProcessingStatus.Done)

Answer 1

IDE 错误不是编译错误（建议使用sbt 及其控制台进行测试）。

您的代码（如下所示）编译正常，无论 IDE 告诉什么（这是错误的）。

import reactivemongo.api.bson._
import scala.util.Try

trait ProcessingStatus {
  def entryName = "foo"
}

object JsonSerialization {
  implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
    override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
  }
}

import JsonSerialization._

BSON.write(new ProcessingStatus {})

Note.1： writeTry 不会覆盖任何内容，因此修饰符是无用的（并且可能导致误解）。

注 2： Try(..) 具有纯值，例如 BSONString(t.entryName) 是过度设计的，而是使用 Success(..)。

注3： 方便的工厂有val w = BSONWriter[T] { t => ... }等。

---

编辑：

类型类BSONWriter（与大多数类型类一样）是不变的，因此在隐式范围内拥有BSONWriter[T] 不允许解析BSONWriter[U] forSome { U <: T }。

trait ProcessingStatus {
  def entryName: String
}

object ProcessingStatus {
  case object Done extends ProcessingStatus { val entryName = "done" }
}

object JsonSerialization {
  implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
    override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
  }
}

import JsonSerialization._

BSON.write(ProcessingStatus.Done
/*
<console>:32: error: could not find implicit value for parameter writer: reactivemongo.api.bson.BSONWriter[ProcessingStatus.Done.type]
       BSON.write(ProcessingStatus.Done)
 */

// --- BUT ---

BSON.write(ProcessingStatus.Done: ProcessingStatus)
// Success(BSONString(done))

在 API 中将 Done（和其他情况）暴露为 ProcessingStatus 也有效。

import reactivemongo.api.bson._
import scala.util.Try

sealed trait ProcessingStatus {
  def entryName: String
}

object ProcessingStatus {
  val Done: ProcessingStatus = new ProcessingStatus { val entryName = "done" }
}

object JsonSerialization {
  implicit object ProcessingStatusWriter extends BSONWriter[ProcessingStatus] {
    override def writeTry(t: ProcessingStatus): Try[BSONString] = Try(BSONString(t.entryName))
  }
}

import JsonSerialization._

BSON.write(ProcessingStatus.Done)