Sangria Snippets

LocaleSupport.scala

// When using an Input field in which you would like to enforce validation at query validation time
// via.... types, you will need a custom JSON marshaller, as well as a `ScalarType` to allow for... 
// custom scalar types to be used as an Input. This does not come up as often for custom output types
// as `.toString` allows for most complex types to be easily serialized as a `String`
object LocaleSupport {
  import io.circe.Decoder

  private val VIOLATION_MESSAGE = "Invalid Locale Provided"

  // Custom Java Exception
  final case class InvalidLocaleException(
    private val message: String = VIOLATION_MESSAGE,
    private val cause: Throwable = None.orNull
  ) extends Exception(message, cause)

  // Sangria Violation
  case object LocaleViolation extends ValueCoercionViolation(VIOLATION_MESSAGE)

  // Implement however
  def parseLocale(s: String): Either[LocaleViolation.type, Locale] = ???

  // JSON decoding
  implicit val decodeLocale: Decoder[Locale] = Decoder.decodeString.emapTry{ s => {
    val res = parseLocale(s)
    res match {
      case Right(l) => Success(l)
      case Left(_) => Failure(new InvalidLocaleException)
    }
  }}

  implicit val LocaleType: ScalarType[Locale] = ScalarType[Locale]("Locale",
    coerceOutput = (d, _) => d.toString,
    coerceUserInput = {
      case s: String => parseLocale(s)
      case _ => Left(LocaleViolation)
    },
    coerceInput = {
      case sangria.ast.StringValue(s, _, _, _, _) => parseLocale(s)
      case _ => Left(LocaleViolation)
    })
}