mongodb - ADT 的编解码器不编译

Question

我正在使用 scala 驱动程序与 mongodb 进行 IO 操作。我的Scala版本是2.11.11 mongo db 驱动程序是 2.2.0 .

我以关于 ADT 的文档为例:

sealed class Tree
case class Branch(b1: Tree, b2: Tree, value: Int) extends Tree
case class Leaf(value: Int) extends Tree

val codecRegistry = fromRegistries( fromProviders(classOf[Tree]), DEFAULT_CODEC_REGISTRY )

这段代码没有编译。

No known subclasses of the sealed class
[error]     val codecRegistry = fromRegistries( fromProviders(classOf[Tree]), DEFAULT_CODEC_REGISTRY )
[error]                                                              ^
[error] knownDirectSubclasses of Tree observed before subclass Branch registered
[error] knownDirectSubclasses of Tree observed before subclass Leaf registered

我错过了什么 ？

更新

下面是我正在做的事情的完整示例。
build.sbt

name := "mongodb-driver-test"

version := "1.0"

scalaVersion := "2.11.11"

libraryDependencies += "org.mongodb.scala" %% "mongo-scala-driver" % "2.2.0"

文件 Models.scala

import org.mongodb.scala.bson.codecs.{DEFAULT_CODEC_REGISTRY, Macros}
import org.bson.codecs.configuration.CodecRegistries.{fromProviders, fromRegistries}

/**
  * Created by alifirat on 02/01/18.
  */


object Models {

  sealed class Tree
  case class Branch(b1: Tree, b2: Tree, value: Int) extends Tree
  case class Leaf(value: Int) extends Tree

  val treeCodec = Macros.createCodecProvider[Tree]()

  val treeCodecRegistry = fromRegistries( fromProviders(treeCodec), DEFAULT_CODEC_REGISTRY )

}

然后，只需执行以下操作:
sbt compile
你会得到 :

[error]   val treeCodec = Macros.createCodecProvider[Tree]()
[error]                                                   ^
[error] knownDirectSubclasses of Tree observed before subclass Branch registered
[error] knownDirectSubclasses of Tree observed before subclass Leaf registered
[error] three errors found
[error] (compile:compileIncremental) Compilation failed

如果我将 Scala 版本更改为 2.12.0 , 我在编译时没有任何错误...

Answer 1

我正在使用驱动程序版本 2.6.0 和 Scala 版本 2.12.8，但仍然遇到同样的问题。

我的解决方法是删除关键字 sealed前面那个密封类，编译，放回去，再编译。但是非常麻烦。