玩 2.4 参数化代数数据类型 JSON 验证

Posted 2023-04-01

【中文标题】玩 2.4 参数化代数数据类型 JSON 验证

【英文标题】：Play 2.4 parameterized algebraic data types JSON validation

【发布时间】：2016-04-14 18:50:20

【问题描述】：

是否可以在 Scala / Play 2.4 中做类似的事情：

sealed trait Location  val `type`: String 
case class CityLocation(zip_code: String, override val `type`: String = "city") extends Location
case class AddressLocation(
  society: Option[String],
  first_name: String,
  last_name: String,
  ...
  override val `type`: String = "address"
) extends Location

sealed trait Point[T <: Location]  val `type`: String; val location: T 
case class ShippingPoint[T](override val location: T, override val `type`: String = "shipping") extends Point[T]
case class PickupPoint[T](override val location: T, override val `type`: String = "pickup") extends Point[T]

object CityLocation 
  implicit val format = Json.format[CityLocation]

object AddressLocation 
  implicit val format = Json.format[AddressLocation]

object ShippingPoint 
  implicit def write[T] = Json.writes[ShippingPoint[T]]
  implicit def read[T]: Reads[ShippingPoint[T]] = (
    (__ \ "location").read[T] and
      (__ \ "type").read[String](exactWordRead("shipping", "error.route.shipping.type"))
  )(ShippingPoint[T].apply _)

object PickupPoint 
  implicit def write[T] = Json.writes[ShippingPoint[T]]
  implicit def read[T]: Reads[PickupPoint[T]] = (
    (__ \ "location").read[T] and
      (__ \ "type").read[String](exactWordRead("pickup", "error.route.pickup.type"))
  )(PickupPoint[T].apply _)

??

目前，它无法编译。

exactWordRead 方法定义如下：

def exactWordRead(word: String, errorMessage: String): Reads[String] = Reads.constraints.pattern(s"^$word$"$"".r, errorMessage)

---

编辑：

由于这个答案https://***.com/a/29834113/2431728，我似乎向前迈出了一步：

sealed trait Location  val `type`: String 
case class CityLocation(zip_code: String, override val `type`: String = "city") extends Location
case class AddressLocation(
  society: Option[String],
  first_name: String,
  last_name: String,
  ...
  override val `type`: String = "address"
) extends Location

sealed trait Point[T <: Location]  val location: T; val `type`: String 
case class ShippingPoint[T](override val location: T, override val `type`: String = "shipping") extends Point[T]
case class PickupPoint[T](override val location: T, override val `type`: String = "pickup") extends Point[T]

object CityLocation 
  implicit val format = Json.format[CityLocation]

object AddressLocation 
  implicit val format = Json.format[AddressLocation]

object ShippingPoint 
  implicit def format[T: Format]: Format[ShippingPoint[T]] = (
    (__ \ "location").format[T] and
      (__ \ "type").format[String](exactWordRead("shipping", "error.route.shipping.type"))
  )(ShippingPoint.apply, unlift(ShippingPoint.unapply))

object PickupPoint 
  implicit def format[T: Format]: Format[PickupPoint[T]] = (
    (__ \ "location").format[T] and
      (__ \ "type").format[String](exactWordRead("pickup", "error.route.pickup.type"))
  )(PickupPoint.apply, unlift(PickupPoint.unapply))

但是，我还没有编译。编译错误是：

[error] type arguments [T] do not conform to trait Point's type parameter bounds [T <: services.coliswebApi.data.Location]
[error] case class ShippingPoint[T](override val location: T, override val `type`: String = "shipping") extends Point[T]
[error]                                                                                                         ^
[error] type arguments [T] do not conform to trait Point's type parameter bounds [T <: services.coliswebApi.data.Location]
[error] case class PickupPoint[T](override val location: T, override val `type`: String = "pickup") extends Point[T]

【参考方案1】：

正如编译器所说，一方面你有，

sealed trait Point[T <: Location]

...另一方面，

case class ShippingPoint[T](???) extends Point[T]
case class PickupPoint[T](???) extends Point[T]

但ShippingPoint 和PickupPoint 的声明中没有任何内容证明类型参数与约束<: Location 兼容，需要扩展Point。

所以你需要解决这个问题。

case class ShippingPoint[T <: Location](???) extends Point[T]
case class PickupPoint[T <: Location](???) extends Point[T]

【讨论】：

确实如此。但现在是无法编译的格式。你知道如何纠正它们吗？

原因是一样的。

确实如此。感谢您的帮助 =)

【参考方案2】：

我认为您还需要像这样以格式绑定您的类型

implicit def format[T <: Location: Format]: Format[ShippingPoint[T]] = (
        (__ \ "location").format[T] and
        (__ \ "type").format[String](exactWordRead("shipping",   "error.route.shipping.type"))
    )(ShippingPoint.apply, unlift(ShippingPoint.unapply))

【讨论】：

它编译！ Thaaaanks 很多 =D