[英]Alternative to parsing json with option [ either [A,B ] ] in scala
例如,这里的payload
是可选的,它有 3 个变体:
如何使用 option[either[A,B,C]] 之类的类型解析 json,但使用密封特征或总和类型使用抽象数据类型?
下面是一个带有一些样板的最小示例:
https://scalafiddle.io/sf/K6RUWqk/1
// Start writing your ScalaFiddle code here
val json =
"""[
{
"id": 1,
"payload" : "data"
},
{
"id": 2.1,
"payload" : {
"field1" : "field1",
"field2" : 5,
"field3" : true
}
},
{
"id": 2.2,
"payload" : {
"field1" : "field1",
}
},
{
"id": 3,
payload" : 4
},
{
"id":4,
"
}
]"""
final case class Data(field1: String, field2: Option[Int])
type Payload = Either[String, Data]
final case class Record(id: Int, payload: Option[Payload])
import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
implicit final val dataDecoder: Decoder[Data] = deriveDecoder
implicit final val payloadDecoder: Decoder[Payload] = Decoder[String] either Decoder[Data]
implicit final val recordDecoder: Decoder[Record] = deriveDecoder
val result = io.circe.parser.decode[List[Record]](json)
println(result)
您的代码几乎没问题,您的 json 中只有语法问题,并且Record.id
应该是Double
而不是Int
- 因为这是您的 json ( "id": 2.1
) 中该字段的显示方式。 请在下面找到固定版本:
val json =
s"""[
{
"id": 1,
"payload" : "data"
},
{
"id": 2.1,
"payload" : {
"field1" : "field1",
"field2" : 5,
"field3" : true
}
},
{
"id": 2.2,
"payload" : {
"field1" : "field1"
}
},
{
"id": 3,
"payload" : 4
},
{
"id": 4
}
]"""
type Payload = Either[String, Data]
final case class Data(field1: String, field2: Option[Int])
final case class Record(id: Double, payload: Option[Payload]) // id is a Double in your json in some cases
import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
implicit val dataDecoder: Decoder[Data] = deriveDecoder
implicit val payloadDecoder: Decoder[Payload] = Decoder[String] either Decoder[Data]
implicit val recordDecoder: Decoder[Record] = deriveDecoder
val result = io.circe.parser.decode[List[Record]](json)
println(result)
在我的情况下产生的:
Right(List(Record(1.0,Some(Left(data))), Record(2.1,Some(Right(Data(field1,Some(5))))), Record(2.2,Some(Right(Data(field1,None)))), Record(3.0,Some(Left(4))), Record(4.0,None)))
更新:
更通用的方法是使用所谓的Sum Types
或简单地说 - 具有几种不同实现的通用sealed trait
。 请参阅下一个 Circe 文档页面以获取更多详细信息: https : //circe.github.io/circe/codecs/adt.html
在你的情况下,它可以实现如下:
import cats.syntax.functor._
import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
sealed trait Payload
object Payload {
implicit val decoder: Decoder[Payload] = {
List[Decoder[Payload]](
Decoder[StringPayload].widen,
Decoder[IntPayload].widen,
Decoder[ObjectPayload].widen
).reduce(_ or _)
}
}
case class StringPayload(value: String) extends Payload
object StringPayload {
implicit val decoder: Decoder[StringPayload] = Decoder[String].map(StringPayload.apply)
}
case class IntPayload(value: Int) extends Payload
object IntPayload {
implicit val decoder: Decoder[IntPayload] = Decoder[Int].map(IntPayload.apply)
}
case class ObjectPayload(field1: String, field2: Option[Int]) extends Payload
object ObjectPayload {
implicit val decoder: Decoder[ObjectPayload] = deriveDecoder
}
final case class Record(id: Double, payload: Option[Payload])
object Record {
implicit val decoder: Decoder[Record] = deriveDecoder
}
def main(args: Array[String]): Unit = {
val json =
s"""[
{
"id": 1,
"payload" : "data"
},
{
"id": 2.1,
"payload" : {
"field1" : "field1",
"field2" : 5,
"field3" : true
}
},
{
"id": 2.2,
"payload" : {
"field1" : "field1"
}
},
{
"id": 3,
"payload" : "4"
},
{
"id": 4
}
]"""
val result = io.circe.parser.decode[List[Record]](json)
println(result)
}
在我的情况下产生了下一个输出:
Right(List(Record(1.0,Some(StringPayload(data))), Record(2.1,Some(ObjectPayload(field1,Some(5)))), Record(2.2,Some(ObjectPayload(field1,None))), Record(3.0,Some(StringPayload(4))), Record(4.0,None)))
希望这可以帮助!
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