Scala Cat library validation list group by Error code - scala

Question

I am new to Scala and functional programming.I did one validation using Scala cat library. But I can't able to group Invalid elements by error code.
case class Err(code: ErrorCode, elementName: String)
This is the output of invalid elements.
List(Invalid(NonEmptyList(Err(missingElement,Des), Err(InvalidElement,order), Err(InvalidElement,name), Err(InvalidElement,source))))
what I want is something like this
missingElement->List(Des)
InvalidElement->List(order,name,source)
Is there any functionality in cat library itself for this? Or is there any workaround to get this?

Answer 1

Assuming your full structure looks similar to this:
sealed trait ErrorCode
object ErrorCode {
case object MissingElement extends ErrorCode
case object InvalidElement extends ErrorCode
}
final case class Err(code: ErrorCode, elementName: String)
And we have a ValidatedNel[Err, ?]:
val res: ValidatedNel[Err, String] =
Invalid(
NonEmptyList(
Err(ErrorCode.MissingElement, "Des"),
List(
Err(ErrorCode.InvalidElement, "order"),
Err(ErrorCode.InvalidElement, "name"),
Err(ErrorCode.InvalidElement, "source")
)
)
)
Then what you'd need to do in order to group the list would be to use groupBy on the error side, using leftMap:
val groupedErrs: Validated[Map[ErrorCode, List[String]], String] =
res.leftMap(
_.toList
.groupBy(_.code)
.map { case (code, errs) => code -> errs.map(_.elementName) }
)
Result:
Invalid(Map(InvalidElement -> List(order, name, source), MissingElement -> List(Des)))
If all this is inside a list of validations, List[ValidatedNel[Err, ?]], then we just need an additional map operation to iterate the list:
val groupedErrs: List[Validated[Map[ErrorCode, List[String]], String]] =
res.map(
_.leftMap(
_.toList
.groupBy(_.code)
.map { case (code, errs) => code -> errs.map(_.elementName) }
)
)
Result:
List(Invalid(Map(InvalidElement -> List(order, name, source), MissingElement -> List(Des))))