播放如何为包含枚举的案例 class 实施隐式写入或格式

Question

下面的展示了如何使用 case class.

将枚举绑定到表单

但是在 Play 2.7.3 中，这段代码失败了：

No Json serializer found for type jura.SearchRequest. Try to implement an implicit Writes or Format for this type.

当我实现格式化程序时：

object SearchRequest {
  implicit val searchRequestFormat: OFormat[SearchRequest] = Json.format[SearchRequest]
}

我明白了

No instance of play.api.libs.json.Format is available for scala.Enumeration.Value in the implicit scope

我应该尝试为系统 scala.Enumeration 类型编写格式化程序吗？
或者当涉及枚举时，是否有另一种方法来实现格式化程序？

测试用例here.

Answer 1

要像cchantep说的那样将枚举写成字符串可以使用Writes.enumNameWrites，我们专门用来读写ID。因此我们在全局包中有一个 EnumFormat 用于枚举：

package object enums {

  implicit def reads[E <: Enumeration](enum: E): Reads[E#Value] = new Reads[E#Value] {
    def reads(json: JsValue): JsResult[E#Value] = json match {
      case JsNumber(s) =>
        try {
          JsSuccess(enum.apply(s.toInt))
        } catch {
          case _: NoSuchElementException => JsError(s"Enumeration expected of type: '${enum.getClass}', but it does not appear to contain the value: '$s'")
        }
      case _ => JsError("Number value expected")
    }
  }

  implicit def writes[E <: Enumeration]: Writes[E#Value] = new Writes[E#Value] {
    def writes(v: E#Value): JsValue = JsNumber(v.id)
  }

  implicit def formatID[E <: Enumeration](enum: E): Format[E#Value] =
    Format(reads(enum), writes)


  def readsString[E <: Enumeration](enum: E): Reads[E#Value] = new Reads[E#Value] {
    def reads(json: JsValue): JsResult[E#Value] = json match {
      case JsString(s) => {
        try {
          JsSuccess(enum.withName(s))
        } catch {
          case _: NoSuchElementException => JsError(s"Enumeration expected of type: '${enum.getClass}', but it does not appear to contain the value: '$s'")
        }
      }
      case _ => JsError("String value expected")
    }
  }

  implicit def writesString[E <: Enumeration]: Writes[E#Value] = new Writes[E#Value] {
    def writes(v: E#Value): JsValue = JsString(v.toString)
  }

  implicit def formatString[E <: Enumeration](enum: E): Format[E#Value] =
    Format(readsString(enum), writesString)
}

并使用：

object SearchRequest extends Enumeration(1) {
  type SearchRequest = Value

  val ONE /*1*/ , TWO /*2*/ , ETC /*n*/ = Value

  implicit val searchRequestFormat: Format[SearchRequest] = formatID(SearchRequest)
}

Answer 2

将以下内容添加到您的枚举对象

implicit object MatchFilterTypeFormatter extends Formatter[MatchFilterType.Value] {
    override val format = Some(("format.enum", Nil))
    override def bind(key: String, data: Map[String, String]) = {
      try {
        Right(MatchFilterType.withName(data.get(key).head))
      } catch {
        case e:NoSuchElementException =>  Left(Seq(play.api.data.FormError(key, "Invalid MatchFilterType Enumeration")))
      }
    }
    override def unbind(key: String, value: MatchFilterType.Value) = {
      Map(key -> value.toString)
    }
  }
  implicit val matchFilterTypeFormat = new Format[MatchFilterType.MatchFilterType] {
    def reads(json: JsValue) = JsSuccess(MatchFilterType.withName(json.as[String]))
    def writes(myEnum: MatchFilterType.MatchFilterType) = JsString(myEnum.toString)
  }

然后题中给出的Formatter/Controller就可以了

一个有效的测试用例是 here。

Answer 3

我将此库用于任何枚举：enumeratum

使用 Dotty 将会有很棒的 Enumerations，但在那之前我想转向 enumeratum 是在 Scala 中处理枚举的最佳方式。另见 Dotty - Enumerations。

作为奖励，有一个 play-json 扩展，请参阅 Play JSON Extension。

有了这个，您的代码将如下所示：

import enumeratum.{ PlayJsonEnum, Enum, EnumEntry }

sealed trait SearchRequest extends EnumEntry

object SearchRequest extends Enum[SearchRequest] with PlayJsonEnum[SearchRequest] {

  val values = findValues

  case object SuperRequest  extends SearchRequest
  case object SimpleRequest extends SearchRequest
  ..
}

本质上，PlayJsonEnum[SearchRequest] 完成了所有工作。

播放如何为包含枚举的案例 class 实施隐式写入或格式

Play how to implement an implicit Writes or Format for a case class including an Enumeration

forms

enums

scala

playframework