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Add docs for Scala 3 enum derivation #2334

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Merged
jatcwang merged 1 commit into from
Oct 29, 2025
Merged

Add docs for Scala 3 enum derivation #2334

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4 changes: 2 additions & 2 deletions modules/core/src/main/scala-3/doobie/util/package.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +15,8 @@ private[util] inline final def summonLabels[T <: Tuple]: List[String] =
private[util] inline final def summonSingletonCases[T <: Tuple, A](inline typeName: String): List[A] =
inline erasedValue[T] match
case _: EmptyTuple => Nil
case _: (h *: t) =>
case _: (h *: t) =>
inline summonInline[Mirror.Of[h]] match
case m: Mirror.Singleton => m.fromProduct(EmptyTuple).asInstanceOf[A] :: summonSingletonCases[t, A](typeName)
case m: Mirror =>
case m: Mirror =>
error("Enum " + typeName + " contains non singleton case " + constValue[m.MirroredLabel])
9 changes: 7 additions & 2 deletions modules/core/src/test/scala-3/doobie/util/GetSuitePlatform.scala
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Expand Up @@ -46,9 +46,14 @@ trait GetDBSuitePlatform { self: munit.CatsEffectSuite & TransactorProvider =>
given Get[EnumWithOnlySingletonCases] = Get.deriveEnumString

test("Get should properly read existing value of enum") {
sql"select 'One'".query[EnumWithOnlySingletonCases].unique.transact(xa).attempt.assertEquals(
sql"select 'One', 'Two', 'Three'".query[(
EnumWithOnlySingletonCases,
EnumWithOnlySingletonCases,
EnumWithOnlySingletonCases)].unique.transact(xa).attempt.assertEquals(
Right(
EnumWithOnlySingletonCases.One
EnumWithOnlySingletonCases.One,
EnumWithOnlySingletonCases.Two,
EnumWithOnlySingletonCases.Three
)
)
}
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19 changes: 19 additions & 0 deletions modules/docs/src/main/mdoc/docs/12-Custom-Mappings.md
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Expand Up @@ -177,6 +177,25 @@ implicit val jsonMeta: Meta[Json] =

There are similar constructors for array types and other possibilities, but `other` is by far the most common in user code and we won't discuss the others here. See the Scaladoc for more information.

## Derivation for Scala 3 enums

You can derive `Get` and `Put` instances for Scala 3 enums using the `Get.deriveEnumString` or `Put.deriveEnumString`.

```scala
enum Color:
case Red, Green, Blue

object Color:
given Get[Color] = Get.deriveEnumString[Color]
given Put[Color] = Put.deriveEnumString[Color]

fr"SELECT 'Red'".query[Color].unique
```

As shown above,

- The instances need to be explicitly derived
- The string values converts from/to are the literal name of the enum cases

## Column Vector Mappings

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