While using databases storing json documents (MongoDB, ElasticSearch) someone could face a problem of decoding/encoding type sums e.g building codecs for navigation tree elements, which have varied types and structure. One should build boilerplate codecs like this one:
sealed trait Node
object Node {
@JsonCodec
case class Folder(val id: String, name: String, folderSpecialField: Option[String]) extends Node
@JsonCodec
case class ListNode(val id: String, name: String, listSpecialField: Option[Int]) extends Node
implicit val encoder: Encoder[Node] = new Encoder[Node] {
override def apply(a: Node): Json = {
val body = a match {
case f: Folder => f.asJson
case ln: ListNode => ln.asJson
}
val hint = Json.obj("hint" -> Json.fromString(a.getClass.getSimpleName))
body.deepMerge(hint)
}
}
implicit val decoder: Decoder[Node] = new Decoder[Node] {
override def apply(c: HCursor): Decoder.Result[Node] = {
c.downField("hint").as[String].flatMap {
case "ListNode" => c.as[Node.ListNode]
case "Folder" => c.as[Node.Folder]
}
}
}
}This minimal library allows automatic building of boilerplate codecs like this, you just need to add annotation to sealed trait:
import io.github.simulacrumx.tscodec._
@TypeSumCodec
sealed trait Node
object Node {
@JsonCodec
case class Folder(val id: String, name: String, folderSpecialField: Option[String]) extends Node
@JsonCodec
case class ListNode(val id: String, name: String, listSpecialField: Option[Int]) extends Node
}
You also can configure the key of type hints, that will be stored inside documents:
import io.github.simulacrumx.tscodec._
@TypeSumCodec(typeHint = "abcdef")
sealed trait Node
object Node {
@JsonCodec
case class Folder(val id: String, name: String, folderSpecialField: Option[String]) extends Node
@JsonCodec
case class ListNode(val id: String, name: String, listSpecialField: Option[Int]) extends Node
}Inheritants of sealed trait should be inside companion object of the trait, otherwise macro would not be working properly
libraryDependencies ++= Seq(
"io.github.simulacrumx" %% "type-sum-codec" % "0.1.1"
)