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scala - 将 Json 从蛇案例解析为骆驼案例

问题描述

所以我有一个这种格式的 JSON，我试图将它从蛇案例转换为与相应案例类匹配的骆驼案例

 val json = """
      {
        "items": [
        {
          "id": "7913",
          "route_id": "33",
          "predictable": true,
          "run_id": "33_486_1",
          "latitude": 34.0234949,
          "longitude": -118.398712,
          "heading": 236,
          "seconds_since_report": 59
        },
        {
          "id": "4140",
          "route_id": "76",
          "predictable": true,
          "run_id": "76_174_0",
          "latitude": 34.0331945,
          "longitude": -118.2646534,
          "heading": 122,
          "seconds_since_report": 12
        },
        {
          "id": "7620",
          "route_id": "20",
          "predictable": true,
          "run_id": "20_669_0",
          "latitude": 34.013733,
          "longitude": -118.490067,
          "heading": 334,
          "seconds_since_report": 172
        }
        ]
      }
      """.stripMargin

我想转换成

  final case class Sample(
    id: Int,
    routeId: Int,
    predictable: Boolean,
    runId: String,
    latitude: Double,
    longitude: Double,
    heading: Int,
    secondsSinceReport: Int
  )

尝试使用

implicit val sampleDecoder = Decoder[List[Sample]].prepare(_.downField("items"))
val decodingResult = parser.decode(json)(sampleDecoder)

但结果是

Attempt to decode value on failed cursor: DownField(routeId),DownArray,DownField(items)

但是，如果我从案例类中用骆驼案例注释掉字段，我会得到

Sample(7913,true,34.0234949,-118.398712,236)
Sample(4140,true,34.0331945,-118.2646534,122)
Sample(7620,true,34.013733,-118.490067,334)

标签： scalacirce

解决方案

您的用例直接来自文档：https ://circe.github.io/circe/codecs/custom-codecs.html

import io.circe.generic.extras._, io.circe.syntax._
// import io.circe.generic.extras._
// import io.circe.syntax._

implicit val config: Configuration = Configuration.default.withSnakeCaseMemberNames
// config: io.circe.generic.extras.Configuration = Configuration(io.circe.generic.extras.Configuration$$$Lambda$9172/0x0000000801132040@69e0f3f6,io.circe.generic.extras.Configuration$$$Lambda$9171/0x0000000801133040@66433b0e,false,None,false)

@ConfiguredJsonCodec case class User(firstName: String, lastName: String)
// defined class User
// defined object User

User("Foo", "McBar").asJson
// res1: io.circe.Json =
// {
//   "first_name" : "Foo",
//   "last_name" : "McBar"
// }

您需要 generic-extras 依赖项build.sbt：

libraryDependencies ++= Seq(
  "io.circe" %% "circe-core",
  "io.circe" %% "circe-generic",
  "io.circe" %% "circe-generic-extras",
  "io.circe" %% "circe-parser"
).map(_ % circeVersion)

addCompilerPlugin("org.scalamacros" %% "paradise" % "2.1.1" cross CrossVersion.full)

文档说您不需要 2.13.x 中的编译器插件，但我无法编译它。天堂还没有发布 2.13.x。所以这个解决方案只适用于 2.12 和更早的版本（还）。

如果它是一次性的，您可以在没有编译器宏的情况下手动进行转换：


   implicit val decodeSample: Decoder[Sample] = new Decoder[Sample] {
     final def apply(c: HCursor): Decoder.Result[Sample] =
       for {
         id <- c.downField("id").as[Int]
         routeId <- c.downField("route_id").as[Int]
         predictable <- c.downField("predictable").as[Boolean]
         runId <- c.downField("run_id").as[String]
         latitude <- c.downField("latitude").as[Double]
         longitude <- c.downField("longitude").as[Double]
         heading <- c.downField("heading").as[Int]
         secondsSinceReport <- c.downField("seconds_since_report").as[Int]
       } yield {
         new Sample(id, routeId, predictable, runId, latitude, longitude, heading, secondsSinceReport)
       }
   }

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