json - 使用 Scala/Play 将 JSON 转换为带有嵌套对象的 case 类

Question

假设我正在使用的 JSON 响应格式如下:

[
    {
       "make": "Tesla",
       "model": "Model S",
       "year": 2017,
       "color": "red",
       "owner": "Bob",
       "max_speed": 200,
       "wheel_size": 30,
       "is_convertible": true,
       "license": "ABC123",
       "cost": 50000,
       "down_payment": 2500,
       "other_property_1": 1,
       "other_property_2": 2,
       "other_property_3": 3,
       "other_property_4": 4,
       "other_property_5": 5,
       "other_property_6": 6,
       "other_property_7": 7,
       "other_property_8": 8,
       "other_property_9": 9,
       "other_property_10": 10,
       "other_property_11": 11
    }
]

这里的 JSON 是一个汽车对象数组(为简单起见，只有 1 个)，我正在尝试使用 JSON Reads 转换器将其转换为模型。假设我有一个 Car case 类来表示每个对象，并且该类有一个嵌套的 FinancialInfo case 类来逻辑地拆分属性数量，从而避免 Scala 的 22 个参数限制。

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

case class Car(
    make: String,
    model: String,
    year: Int,
    color: String,
    owner: String,
    maxSpeed: Int,
    wheelSize: Int,
    isConvertible: Boolean,
    license: String,
    financialInfo: FinancialInfo, // nested case class to avoid 22 param limit
    otherProperty1: Int,
    otherProperty2: Int,
    otherProperty3: Int,
    otherProperty4: Int,
    otherProperty5: Int,
    otherProperty6: Int,
    otherProperty7: Int,
    otherProperty8: Int,
    otherProperty9: Int,
    otherProperty10: Int,
    otherProperty11: Int
)

object Car {
    implicit val reads: Reads[Car] = (
        (__ \ "make").read[String] and
        (__ \ "model").read[String] and
        (__ \ "year").read[Int] and
        (__ \ "color").read[String] and
        (__ \ "owner").read[String] and
        (__ \ "max_speed").read[Int] and
        (__ \ "wheel_size").read[Int] and
        (__ \ "is_convertible").read[Boolean] and
        (__ \ "license").read[String] and
        (__ \ "financialInfo").read[FinancialInfo] and
        (__ \ "other_property_1").read[Int] and
        (__ \ "other_property_2").read[Int] and
        (__ \ "other_property_3").read[Int] and
        (__ \ "other_property_4").read[Int] and
        (__ \ "other_property_5").read[Int] and
        (__ \ "other_property_6").read[Int] and
        (__ \ "other_property_7").read[Int] and
        (__ \ "other_property_8").read[Int] and
        (__ \ "other_property_9").read[Int] and
        (__ \ "other_property_10").read[Int] and
        (__ \ "other_property_11").read[Int]
    )(Car.apply _)
}

case class FinancialInfo(
   cost: BigDecimal,
   downPayment: BigDecimal
)

object FinancialInfo {
    implicit val reads: Reads[FinancialInfo] = (
        (__ \ "cost").read[BigDecimal] and
        (__ \ "down_payment").read[BigDecimal]
    )(FinancialInfo.apply _)
}

但是，我猜测是因为 JSON 中没有名为 financialInfo 的属性。 ，它没有正确解析它。在我的实际应用程序中，当我使用 response.json.validate[List[Car]] 时出现此错误:

JsError(List(((0)/financialInfo,List(JsonValidationError(List(error.path.missing),WrappedArray()))))) 

总而言之，在示例中，cost和 down_payment不包含在嵌套对象中，即使对于 Car case 类我必须包含一个名为 financialInfo 的嵌套模型.解决此错误并确保 cost 的值的最佳方法是什么？和 down_payment可以解析吗？任何帮助或见解将不胜感激!

Answer 1

Reads可以相互组合和包含。

所以，有:

implicit val fiReads: Reads[FinancialInfo] = (
  (JsPath \ "cost").read[BigDecimal] and
  (JsPath \ "down_payment").read[BigDecimal]
  )(FinancialInfo.apply _)

我们可以将它包含在父级 Reads 中:

implicit val carReads: Reads[Car] = (
  (JsPath \ "make").read[String] and
  (JsPath \ "model").read[String] and
  fiReads  // <--- HERE!
)(Car.apply _)

现在，使用以下 JSON:

private val json =
  """
    |[
    |    {
    |       "make": "Tesla",
    |       "model": "Model S",
    |       "cost": 50000,
    |       "down_payment": 2500
    |    },
    |    {
    |       "make": "Tesla",
    |       "model": "Model D",
    |       "cost": 30000,
    |       "down_payment": 1500
    |    }
    |]
  """.stripMargin

val parsedJsValue = Json.parse(json)
val parsed = Json.fromJson[List[Car]](parsedJsValue)

println(parsed)

它被正确解析:

JsSuccess(List(Car(Tesla,Model S,FinancialInfo(50000,2500)), Car(Tesla,Model D,FinancialInfo(30000,1500))),)

附言Reads原题中不需要包裹成不同的object s。相关的隐式值在同一范围内会更好，更接近它们实际使用的位置。