Hello everyone! I'm trying to write some custom scalar for LocalDate but I'm currently stuck with an...

# graphql-kotlin

[Roy Åne Sylthe]

Hello everyone! I'm trying to write some custom scalar for LocalDate but I'm currently stuck with an issue I'm having some real trouble solving. I'm sending in some data to my mutator, along with it a date string formatted like "1989-04-24", and I'm met with an exception telling me
`Cannot construct instance of java.time.LocalDate (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)`

object DateCoercing : Coercing<Date, String> {

  override fun parseValue(input: Any?): Date = try {
    LocalDate.parse(serialize(input))
  } catch (e: DateTimeParseException) {
    throw CoercingParseValueException("...", e)
  }

  override fun parseLiteral(input: Any?): Date? = try {
    (input as? StringValue)?.value?.let { LocalDate.parse(it) }
  } catch (e: DateTimeParseException) {
    throw CoercingParseLiteralException("...", e)
  }

  override fun serialize(dataFetcherResult: Any?): String = dataFetcherResult.toString()
}

I've tried most of the common solutions found by Googling to no avail...

[Robert]

you are mixing java.util.Date and java.time.LocalDate is that intendend?

[Roy Åne Sylthe]

Sorry, that's an alias for LocalDate

[Dariusz Kuc]

have you registered it in your hooks?

[Dariusz Kuc]

exception implies that Jackson attempts to deserialize it directly instead of using the coercing logic

[Roy Åne Sylthe]

@Component
class CustomSchemaGeneratorHooks : SchemaGeneratorHooks {

  override fun willGenerateGraphQLType(type: KType): GraphQLType? = when (type.classifier as? KClass<*>) {
    Date::class -> graphqlDateType
    else -> null
  }
}

val graphqlDateType: GraphQLType? = GraphQLScalarType.newScalar()
  .name("Date")
  .description("...")
  .coercing(DateCoercing)
  .build()

This should be picked up automatically, correct?

[Dariusz Kuc]

your hook is for Date::class yet you are trying to coerce java.time.LocalDate are you sure you are not mixing the two?

[Roy Åne Sylthe]

As I mentioned above, Date is an alias for LocalDate as I'm also using java.time.Instant as a custom scalar that I've given the alias DateTime .

[Dariusz Kuc]

error implies that there is a mismatch somewhere so I’d double check on that

[Dariusz Kuc]

try removing aliases first and verify it works

[Dariusz Kuc]

then once it works you can try re-introducing them

[Roy Åne Sylthe]

I've removed type aliases now and the result is the same, sadly.

[Lenny]

does it need to be Date::class.java in the when expression? i keep doing the wrong thing and immediately forgetting which after i figure it out

[Lenny]

nope, it’s just ::class … got it wrong again

[Dariusz Kuc]

well you can also try configuring jackson with https://github.com/FasterXML/jackson-modules-java8/tree/master/datetime but it should work without it

[Roy Åne Sylthe]

I was using version 1.4.2... for some reason. Updated to 3.1.1 to see if that fixed it and it's now working without needing to change anything!

[Dariusz Kuc]

👍