scala – 具有对象键的记录的Circe通用编解码器派生

发布时间：2020-12-16 18:36:44 所属栏目：安全来源：网络整理

导读：我正在尝试实现类似的东西 object Claims { import shapeless._ import shapeless.labelled.FieldType import io.circe._ import io.circe.generic.semiauto._ import java.util.UUID type ClaimOf[V] = FieldOf[V] object iss extends ClaimOf[String] obje

我正在尝试实现类似的东西

object Claims {
  import shapeless._
  import shapeless.labelled.FieldType
  import io.circe._
  import io.circe.generic.semiauto._
  import java.util.UUID

  type ClaimOf[V] = FieldOf[V]
  object iss extends ClaimOf[String]
  object subj extends ClaimOf[String]
  object aud extends ClaimOf[Set[String]]
  object client_id extends ClaimOf[UUID]

  implicit val encoder =
    deriveEncoder[FieldType[iss.type,String] :: FieldType[subj.type,String] :: HNil]
}

它不会编译错误
error：找不到参数编码的隐含值：shapeless.Lazy [io.circe.generic.encoding.DerivedObjectEncoder [shapeless.:: [shapeless.labelled.FieldType [Claims.iss.type,String],shapeless.:: [ shapeless.labelled.FieldType [Claims.subj.type,字符串],shapeless.HNil]]]]
???????????deriveEncoder [FieldType [iss.type,String] :: FieldType [subj.type,String] :: HNil]

解决方法

根据 Travis Brown,问题是“泛型推导旨在与Shapeless的通用实例一起使用,并期望FieldType键成为符号.” See discussion on Gitter.

我的解决方案

object Claims {
  import shapeless._
  import shapeless.labelled.FieldType
  import io.circe._
  import io.circe.syntax._
  import io.circe.generic.semiauto._
  import io.circe.generic.encoding.DerivedObjectEncoder
  import java.util.UUID

  abstract case class ClaimOf[V](name: String) extends FieldOf[V]

  object iss extends ClaimOf[String]("iss")
  object subj extends ClaimOf[String]("subj")
  object aud extends ClaimOf[Set[String]]("aud")
  object client_id extends ClaimOf[UUID]("client_id")

  implicit final def encodeClaims[K,H,T <: HList](implicit key: Witness.Aux[K],claim: K <:< ClaimOf[H],encodeHead: Lazy[Encoder[H]],encodeTail: Lazy[DerivedObjectEncoder[T]]
                                                      ): DerivedObjectEncoder[FieldType[K,H] :: T] =
  new DerivedObjectEncoder[FieldType[K,H] :: T] {
    final def encodeObject(a: FieldType[K,H] :: T): JsonObject = a match {
      case h :: t =>
        (key.value.name -> encodeHead.value(h)) +: encodeTail.value.encodeObject(t)
    }
  }

  val encoder = deriveEncoder[FieldType[iss.type,String] :: HNil]

  val rec = (iss ->> "issuer") :: (subj ->> "subject") :: HNil

  val json = rec.asJson.spaces2
}

encodeClaims函数基本上是来自circe的原始函数的副本,取代了对键的约束.

This answer可用于实现另一种解决方案.

（编辑：李大同）

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