播放Scala读/写取决于类型

Question

我在播放框架2.3中遇到与Json阅读器打交道的麻烦，具体取决于类字段：

我的模特：

trait Data{
  val id:String
  val type:String
  val creation_date:Date
}

case class Price(
  id:String,
  type:String,
  creation_date:Date,
  amount:Int,
  currency:String) extends Data

case class Weight(
  id:String,
  type:String,
  creation_date:Date,
  value:Int,
  unit_of_measurement:String) extends Data

case class MyObject(
  id:String,
  data:List[Data]
)

我的问题是：如何读取MyObject类并保留Json的所有值，例如：

{
  id:"1",data:
    [
      {
        id:"1",
        type:"price",
        creation_date:"2014-12-01T00:00:00.000Z",
        amount:99,
        currency:"dollar"
      },
      {
        id:"1",
        type:"price",
        creation_date:"2014-12-01T00:00:00.000Z",
        amount:99,
        currency:"dollar"
      },
      {
        id:"1",
        type:"weight",
        creation_date:"2014-12-01T00:00:00.000Z",
        value:2,
        unit_of_measurement:"tonne"
      }
    ]
}

我尝试了这个：

implicit val myObjectReads: Reads[MyObject] = (
  ....
  (__ \ "data").read(Reads.traversableReads[List,Data])

但这不起作用

非常感谢您的帮助 ！

MC

Answer 1

orElse您可以在特征中使用该方法Reads：

import play.api.libs.json.Reads.verifying

val priceReads: Reads[Price] = verifying[Price](_.`type` == "price")(Json.reads[Price])
val weightReads: Reads[Weight] = verifying[Weight](_.`type` == "weight")(Json.reads[Weight])
implicit val dataReads: Reads[Data] = priceReads.map(identity[Data]) orElse weightReads.map(identity[Data])
implicit val myObjectReads: Reads[MyObject] = Json.reads[MyObject]

请注意，我需要在使用之前将Reads[Price]和映射Reads[Weight]到，因为它不是协变的（a不是 a ）。我还添加了读取来检查类型值，如果两者恰好具有相同的结构。Reads[Data]orElseReadsReads[Price]Reads[Data]verifyingPriceWeight