json4s 无法使用 mixin 特征序列化案例类

Question

为什么这不起作用？

object JsonExample extends App {
  import org.json4s._
  import org.json4s.native.Serialization
  import org.json4s.native.Serialization.{read, write}
  implicit val formats = Serialization.formats(NoTypeHints)

  case class Winner(id: Long, numbers: List[Int])    

  trait Greet { val greeting = "hi"}
  val obj = new Winner(1, List(1,2)) with Greet
  println(write(obj))
}

这会打印一个空的 JSON 对象

{}

如果我删除“with Greet”，我会得到(正确的)结果:

{"id":1,"numbers":[1,2]}

Answer 1

看起来如果您对格式更具体，您就可以获得您想要的结果:

import org.json4s.{FieldSerializer, DefaultFormats}
import org.json4s.native.Serialization.write

case class Winner(id: Long, numbers: List[Int])
trait Greet { val greeting = "hi"}

implicit val formats = DefaultFormats + FieldSerializer[Winner with Greet]()

val obj = new Winner(1, List(1,2)) with Greet

//returns {"greeting":"hi","id":1,"numbers":[1,2]}
write(obj)