Play Framework JSON 在排序时失败

Question

我有一大堆案例类，下面只是这些案例类的一个子集：

sealed trait BuiltInType { def id: Int }
case class ZombieType          (a: String,        id: Int = 0) extends BuiltInType
case class BooleanType         (a: Boolean,       id: Int = 1) extends BuiltInType
case class ByteType            (a: Byte,          id: Int = 2) extends BuiltInType
case class UByteType           (a: Byte,          id: Int = 3) extends BuiltInType
case class Int16Type           (a: Int,           id: Int = 4) extends BuiltInType
case class UInt16Type          (a: Int,           id: Int = 5) extends BuiltInType
case class Int32Type           (a: Int,           id: Int = 6) extends BuiltInType
case class UInt32Type          (a: Int,           id: Int = 7) extends BuiltInType
case class Int64Type           (a: Long,          id: Int = 8) extends BuiltInType
case class UInt64Type          (a: Long,          id: Int = 9) extends BuiltInType
case class FloatType           (a: Float,         id: Int = 10) extends BuiltInType
case class DoubleType          (a: Double,        id: Int = 11) extends BuiltInType
case class StringType          (a: String,        id: Int = 12) extends BuiltInType
case class DateTimeType        (a: Long,          id: Int = 13) extends BuiltInType // FIXME: Wrong type used, fix it later
case class GuidType            (a: UUID,          id: Int = 14) extends BuiltInType
case class ByteStringType      (a: Vector[Byte],  id: Int = 15) extends BuiltInType
case class XmlElementType      (a: String,        id: Int = 16) extends BuiltInType
case class NodeIdType          (a: NodeId,        id: Int = 17) extends BuiltInType
case class ExpandedNodeIdType  (a: NodeId,        id: Int = 18) extends BuiltInType // FIXME: Wrong type used, fix it later
case class StatusCodeType      (a: StatusCode,    id: Int = 19) extends BuiltInType
case class QualifiedNameType   (a: QualifiedName, id: Int = 20) extends BuiltInType
case class LocalizedTextType   (a: LocalizedText, id: Int = 21) extends BuiltInType
case class ExtensionObjectType (a: ExtensionObject, id: Int = 22) extends BuiltInType 
case class DataValueType       (a: DataValue,       id: Int = 23) extends BuiltInType 
case class VariantType         (a: Variant,       id: Int = 24) extends BuiltInType
case class DiagnosticInfoType  (a: String,        id: Int = 25) extends BuiltInType 

如您所见，我定义了其他几种复杂类型。例如，有一个名为 Variant 的类型，它本身就是这样的案例类：

sealed trait VariantData
case class SimpleOrder(rows: Vector[BuiltInType]) extends VariantData
case class HigherOrder(matrices: Vector[VariantData]) extends VariantData
case class Variant(data: VariantData)

然后，我像这样定义播放 JSON 所需的所有隐式格式：

implicit val strType = Json.format[StringType]
implicit val guidType = Json.format[GuidType]
implicit val int16Type = Json.format[Int16Type]
implicit val uint64Type = Json.format[UInt64Type]
implicit val int32Type = Json.format[Int32Type]
implicit val int64Type = Json.format[Int64Type]
implicit val uByteTyp = Json.format[UByteType]
implicit val qNameType = Json.format[QualifiedNameType]
implicit val nodeIdTyp = Json.format[NodeIdType]
implicit val locTextTyp = Json.format[LocalizedTextType]
implicit val zombType = Json.format[ZombieType]
implicit val statusCodeTyp = Json.format[StatusCodeType]
implicit val builtInType = Json.format[BuiltInType]
implicit val simpleFmt = Json.format[SimpleOrder]
implicit val higherFmt = Json.format[HigherOrder]
implicit val varDataFmt = Json.format[VariantData]
implicit val varFmt = Json.format[Variant]

我收到此错误：

Error:(66, 43) No instance of Reads is available for domain.CommonTypes.VariantType in the implicit scope (Hint: if declared in the same file, make sure it's declared before)
implicit val builtInType = Json.format[BuiltInType]

所以我像这样更改了隐式的顺序：

implicit val simpleFmt = Json.format[SimpleOrder]
implicit val higherFmt = Json.format[HigherOrder]
implicit val varDataFmt = Json.format[VariantData]
implicit val varFmt = Json.format[Variant]
implicit val strType = Json.format[StringType]
implicit val guidType = Json.format[GuidType]
implicit val int16Type = Json.format[Int16Type]
implicit val uint64Type = Json.format[UInt64Type]
implicit val int32Type = Json.format[Int32Type]
implicit val int64Type = Json.format[Int64Type]
implicit val uByteTyp = Json.format[UByteType]
implicit val qNameType = Json.format[QualifiedNameType]
implicit val nodeIdTyp = Json.format[NodeIdType]
implicit val locTextTyp = Json.format[LocalizedTextType]
implicit val zombType = Json.format[ZombieType]
implicit val statusCodeTyp = Json.format[StatusCodeType]
implicit val builtInType = Json.format[BuiltInType]

但是现在，我收到此错误：

Error:(53, 41) No instance of play.api.libs.json.Format is available for scala.collection.immutable.Vector[domain.CommonTypes.BuiltInType] in the implicit scope (Hint: if declared in the same file, make sure it's declared before)
implicit val simpleFmt = Json.format[SimpleOrder]

所以我现在的问题是，这是一个订购问题还是我错过了一些东西，因为这里的抱怨是它期待一个

矢量[内置类型]

还是循环依赖导致了这个问题？

Answer 1

通常，您始终可以解决以下排序问题：

把formats放在companion-objects.

请参阅下面的示例。

为了简化您的工作sealed traits我会使用play-json 派生的编解码器

进口：

import play.api.libs.json._
import julienrf.json.derived

很酷的是你只需要formattrait，它的所有subclasses都会自动完成：

implicit val jsonFormat: OFormat[VariantData] = derived.oformat[VariantData]()
implicit val jsonFormat: OFormat[BuiltInType] = derived.oformat[BuiltInType]()

format代码略有不同。

为了说明这如何简化代码，这里有Dmytro的例子：

import play.api.libs.json._
import julienrf.json.derived
sealed trait BuiltInType { def id: Int }
case class StringType(a: String, id: Int = 12) extends BuiltInType    
case class ByteStringType(a: Seq[Byte], id: Int = 15) extends BuiltInType    
case class VariantType(a: Variant, id: Int = 24) extends BuiltInType
object BuiltInType {
implicit val jsonFormat: OFormat[BuiltInType] = derived.oformat[BuiltInType]()
}
sealed trait VariantData
case class SimpleOrder(rows: Seq[BuiltInType]) extends VariantData
case class HigherOrder(matrices: Seq[VariantData]) extends VariantData
object VariantData {
implicit val jsonFormat: OFormat[VariantData] = derived.oformat[VariantData]()
}
case class Variant(data: VariantData)
object Variant {
implicit val jsonFormat: OFormat[Variant] = derived.oformat[Variant]()
}
val json = Json.toJson(VariantType(Variant(SimpleOrder(Seq(StringType("aaa"))))): BuiltInType)
println(json) //{"a":{"data":{"_type":"App.SimpleOrder","rows":[{"a":"aaa","_type":"App.StringType","id":12}]}},"_type":"App.VariantType","id":24}

有了你的例子，差异会更大。

Answer 2

不要忘记指定隐式类型并重新排列隐式，以便没有警告

Warning: Reference to uninitialized value ... 
implicit val ...

以下代码似乎适用于 Scala 2.13.0/2.12.8 + play-json 2.7.4

import play.api.libs.json._
object App {
sealed trait BuiltInType { def id: Int }
case class StringType          (a: String,        id: Int = 12) extends BuiltInType
case class ByteStringType      (a: Vector[Byte],  id: Int = 15) extends BuiltInType
case class VariantType         (a: Variant,       id: Int = 24) extends BuiltInType
sealed trait VariantData
case class SimpleOrder(rows: Vector[BuiltInType]) extends VariantData
case class HigherOrder(matrices: Vector[VariantData]) extends VariantData
case class Variant(data: VariantData)
implicit val strType: OFormat[StringType] = Json.format[StringType]
implicit val byteStrType: OFormat[ByteStringType] = Json.format[ByteStringType]    
implicit val varDataFmt: OFormat[VariantData] = Json.format[VariantData]
implicit val builtInType: OFormat[BuiltInType] = Json.format[BuiltInType]
implicit val simpleFmt: OFormat[SimpleOrder] = Json.format[SimpleOrder]
implicit val higherFmt: OFormat[HigherOrder] = Json.format[HigherOrder]
implicit val varFmt: OFormat[Variant] = Json.format[Variant]
implicit val varType: OFormat[VariantType] = Json.format[VariantType]
val json = Json.toJson(VariantType(Variant(SimpleOrder(Vector(StringType("aaa"))))): BuiltInType)
println(json)//{"a":{"data":{"_type":"App.SimpleOrder","rows":[{"a":"aaa","_type":"App.StringType","id":12}]}},"_type":"App.VariantType","id":24}
}