使用Scala / Play将JSON转换为带有嵌套对象的case类

Question

说我正在使用的JSON响应的格式如下：

[
    {
       "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
    }
]

此处的JSON是汽车对象的数组（为简单起见，仅为1），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案例类来表示每个对象，并且该类具有嵌套的FinancialInfo案例类，以在逻辑上拆分属性的数量，从而避免了Scala的22参数限制。

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中没有称为的属性financialInfo，因此无法正确解析它。在我的实际应用程序中，当我使用时遇到此错误response.json.validate[List[Car]]：

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

总而言之，在该示例中，cost并且down_payment不包含在嵌套对象中，即使对于Car case类，我也必须包括一个称为的嵌套模型financialInfo。什么是要解决这个错误的最好方式，并确保为值cost，并down_payment可以对其进行解析？任何帮助或见识将不胜感激！

Answer 1

Reads 可以合并并相互包含。

因此，具有：

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

我们可以将其包含到父对象中Reads：

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))),)

ps Reads原始问题中的不需要包装成不同的objects。在相同范围内，相关的隐式值会更好，更接近它们的实际使用位置。