带有案例类的抽象类的scala circe编码器/解码器答案

【问题标题】：scala circe encoders/decoders for an abstract class with case classes带有案例类的抽象类的scala circe编码器/解码器
【发布时间】：2018-10-22 17:51:34
【问题描述】：

我想将 FieldMapping 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]
}

... 等 - 完整代码在这里： 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) 找不到类型的惰性隐式值 io.circe.generic.decoding.DerivedDecoder[com.example.model.FieldMapping] 隐式 val fooDecoder: Decoder[FieldMapping] = derivedDecoder[FieldMapping] 错误：(14, 65)

deriveDecoder 方法的参数不足：（隐式解码： shapeless.Lazy[io.circe.generic.decoding.DerivedDecoder[com.example.model.FieldMapping]])io.circe.Decoder[com.example.model.FieldMapping]。未指定值参数解码。隐式 val fooDecoder：解码器[FieldMapping] = 派生解码器[FieldMapping] 错误：(15, 65)

找不到类型的惰性隐式值 io.circe.generic.encoding.DerivedObjectEncoder[com.example.model.FieldMapping] 隐式 val fooEncoder: Encoder[FieldMapping] = derivedEncoder[FieldMapping] 错误：(15, 65)

没有足够的论据方法派生编码器：（隐式编码： shapeless.Lazy[io.circe.generic.encoding.DerivedObjectEncoder[com.example.model.FieldMapping]])io.circe.ObjectEncoder[com.example.model.FieldMapping]。未指定的值参数编码。隐式 val fooEncoder：编码器[FieldMapping] = 派生编码器[FieldMapping]

【问题讨论】：

在您的要点中，您没有提供GUser 的代码。
FieldMapping 也没有定义。
如果我注释掉 case class GUserField、def user、import com.example.model...、implicit val fooDecoder、implicit val fooEncoder 一切都会编译。
这里是其余代码 - github.com/alexeyOnGitHub/scala-typesafe/tree/master/src/main/… 我需要 FieldMapping 集合的编码器/解码器，因为这是我想要转换为 json 字符串的内容
How to create a Minimal, Complete, and Verifiable example

标签： scala circe

【解决方案1】：

Field 应该是一个密封特征（具有抽象类或非密封特征这不起作用）。

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]
}

【讨论】：