相关疑难解决方法(0)

我在play scala中有一个等效的以下模型:

case class Foo(id:Int,value:String)
object Foo{
  import play.api.libs.json.Json
  implicit val fooFormats = Json.format[Foo]
}

对于以下Foo实例

Foo(1, "foo")

我会得到以下JSON文档:

{"id":1, "value": "foo"}

此JSON是持久存储的,并从数据存储区读取.现在我的要求已经改变了,我需要为Foo添加一个属性.该属性具有默认值:

case class Foo(id:String,value:String, status:String="pending")

写入JSON不是问题:

{"id":1, "value": "foo", "status":"pending"}

但是从它读取会产生一个JsError,错过了"/ status"路径.

如何以最小的噪音提供默认值？

(ps:我有一个答案,我将在下面发布,但我对此并不满意,并且会赞成并接受任何更好的选择)

我有这个:

package models

import play.api.libs.json._
import play.api.libs.functional.syntax._

object ModelWrites {
    implicit val tmoWrites= Json.writes[TestModelObject]
    implicit val ihWrites = Json.writes[IntHolder]
}

case class TestModelObject(s1:String, s2:String)

case class IntHolder(i1:Int, i2:Int)

trait HasInts {
    val ints: List[IntHolder]
}

当我这样做:

scala> val tmo = new TestModelObject("hello", "world") with HasInts {
  val ints = List(IntHolder(1,2), IntHolder(3,4))
}

scala> Json.toJson(tmo)
res0: play.api.libs.json.JsValue = {"s1":"hello","s2":"world"}

我如何隐瞒序列化混合val'ints'？喜欢:

scala> val someInts = List(IntHolder(8,9), IntHolder(10,11))
someInts: List[models.IntHolder] = List(IntHolder(8,9), IntHolder(10,11))

scala> Json.toJson(someInts)
res1: play.api.libs.json.JsValue = [{"i1":8,"i2":9},{"i1":10,"i2":11}]

注意:如果我尝试:implicit val hasIntsWrites …

假设我有两个特征,我想混合到一个班级.每个特征都实现了类所需的抽象方法.

trait Writable {
    def serialize(out: java.io.DataOutput)
}

trait T1 extends Writable

trait A extends T1 {
   val aNum: Int
   abstract override def serialize(out: java.io.DataOutput) = {
       super.serialize(out)
       println("A serialize")
       out.writeInt(aNum)
   }

   def action = println("A action")
}

trait B extends T1 {
   val bNum: Int
   abstract override def serialize(out: java.io.DataOutput) = {
       super.serialize(out)
       println("B serialize")
       out.writeInt(bNum)
   }

   def action = println("B action")
}

abstract class M[CT1 <: T1](val mNum: Int) extends Writable {
   this: M[CT1] with T1 =>
   def …