带有case类的抽象类的scala-circe编码器/解码器

Question

我想将FieldMmap类的集合保存为json字符串-

abstract class Field {
  def clazz: Class[_]

  def name: String
}

case class StringField(name: String) extends Field {
  override def clazz: Class[_] = classOf[String]
}

case class DateField(name: String) extends Field {
  override def clazz: Class[_] = classOf[Date]
}

... etc-完整代码：https://github.com/alexeyOnGitHub/scala-typesafe/blob/master/src/main/scala/com/example/model/Field.scala

Circe代码：

import com.example.model.{DateField, Field, FieldMapping, StringField}
import io.circe.generic.semiauto.{deriveDecoder, deriveEncoder}
import io.circe.{Decoder, Encoder}

object CirceBoilerplateForConfigs {
  implicit val fieldDecoder: Decoder[StringField] = deriveDecoder[StringField]
  implicit val fieldEncoder: Encoder[StringField] = deriveEncoder[StringField]

  implicit val dateDecoder: Decoder[DateField] = deriveDecoder[DateField]
  implicit val dateEncoder: Encoder[DateField] = deriveEncoder[DateField]

  implicit val fooDecoder: Decoder[FieldMapping] = deriveDecoder[FieldMapping]
  implicit val fooEncoder: Encoder[FieldMapping] = deriveEncoder[FieldMapping]
}

错误：（14，65）找不到io类型的延迟隐式值。circe。通用的解码。DerivedDecoder[com.example.model.FieldMapping]隐式val-fooDecoder:Decoder[FieldMapping]=DerivedDecoder[FieldMapping]错误：（14，65）

没有足够的参数用于方法deriveDecoder：（隐式解码：无形状。懒惰[io.circe.generic.decoding.deriveDecoder[com.example.model.FieldMapping]]）io。circe。解码器[com.example.model.FieldMapping]。未指定值参数解码。隐式val-fooDecoder:Decoder[FieldMapping]=deriveDecoder[FieldMapping]错误：（15，65）

找不到io类型的惰性隐式值。circe。通用的编码。DerivedObjectEncoder[com.example.model.FieldMapping]隐式val fooEncoder:Encoder[FieldMapping]=deriveEncoder[FieldMapping]错误：（15，65）

方法派生的参数不够Encoder：（隐式编码：无形状。Lazy[io.circe.generic.encoding.DerivedObjectEncoder[com.example.model.FieldMap]]）io.circe.ObjectEncoder[com.example.model.FieldMap]。未指定值参数编码。隐式val foEncoder： Encoder[FieldMap]=派生编码器[FieldMap]

Answer 1

字段应为密封特征（对于抽象类或非密封特征，这将不起作用）。

以下代码编译：

import java.util.Date

sealed trait Field {
  def clazz: Class[_]

  def name: String
}

case class StringField(name: String) extends Field {
  override def clazz: Class[_] = classOf[String]
}

case class DateField(name: String) extends Field {
  override def clazz: Class[_] = classOf[Date]
}

case class FieldMapping(fieldInConnector1: Option[Field],
                        fieldInConnector2: Option[Field],
                        selected: Boolean,
                        defaultValue: String)

import io.circe.generic.semiauto.{deriveDecoder, deriveEncoder}
import io.circe.{Decoder, Encoder}
object CirceBoilerplateForConfigs {
  implicit val stringDecoder: Decoder[StringField] = deriveDecoder[StringField]
  implicit val stringEncoder: Encoder[StringField] = deriveEncoder[StringField]

  implicit val dateDecoder: Decoder[DateField] = deriveDecoder[DateField]
  implicit val dateEncoder: Encoder[DateField] = deriveEncoder[DateField]

  implicit val fieldDecoder: Decoder[Field] = deriveDecoder[Field]
  implicit val fieldEncoder: Encoder[Field] = deriveEncoder[Field]

  implicit val fooDecoder: Decoder[FieldMapping] = deriveDecoder[FieldMapping]
  implicit val fooEncoder: Encoder[FieldMapping] = deriveEncoder[FieldMapping]
}