# Kotlinx serialization: How to migrate map from 0.20.0 to 1.0-M1-1.4.0-rc **URL:** \ **Category:** Uncategorized\ **Created:** [September 7, 2020, 10:34am UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069 "2020-09-07T10:34:46Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![arberg](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@arberg](https://discuss.kotlinlang.org/u/arberg)\ **Post date:** [September 7, 2020, 10:34am UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/1 "2020-09-07T10:34:46Z")
Not sure this is the right forum but here goes: We use kotlinx serialization 0.20.0, and just tried migrating to 1.0-M1-1.4.0-rc. We have a map like this ``` @Serializable class TripStorageData { val activeTripMap = mutableMapOf() } @Parcelize @Serializable data class TripId(val serverId: Int, val id: Long, val type: TripType) : Parcelable { override fun toString(): String = """TripId(serverId=$serverId, id=$id, type=TripType.$type)""" } ``` The new serialization version does not support may keys except as enums or primitives. I cannot see that change in the change log, but I suppose that is a changelog omission rather than a bug: [kotlinx.serialization/CHANGELOG.md at master · Kotlin/kotlinx.serialization · GitHub](https://github.com/Kotlin/kotlinx.serialization/blob/master/CHANGELOG.md) How do I migrate my code, and do I really have to use a string? Perhaps I need a custom serialization? I’m not quite sure where to start digging. Any help is appreciated. Best Alex ---
**Author:** ![fvasco](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/fvasco/32/1961_2.png) [@fvasco](https://discuss.kotlinlang.org/u/fvasco)\ **Post date:** [September 8, 2020, 6:42am UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/2 "2020-09-08T06:42:40Z")
Can you provide a better reproducer and explain what is the expected result? ---
**Author:** ![arberg](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@arberg](https://discuss.kotlinlang.org/u/arberg)\ **Post date:** [September 8, 2020, 7:22am UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/3 "2020-09-08T07:22:35Z")
Hi fvasco, That question makes zero sense for me, if it is a feature that map keys can only be enums or primitives. GIven that the compiler says so to me, it is not just a random bug. Why are you asking for a sample? Do you know whether or not it is the case that map keys must now follow that rule? Best Alex ---
**Author:** ![fvasco](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/fvasco/32/1961_2.png) [@fvasco](https://discuss.kotlinlang.org/u/fvasco)\ **Post date:** [September 8, 2020, 8:02am UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/4 "2020-09-08T08:02:12Z")
> [@arberg](#): > > Why are you asking for a sample? It is not clear to me what format are using, what is the error output and what is your goal. > [@arberg](#): > > Do you know whether or not it is the case that map keys must now follow that rule? Yes, I might. ---
**Author:** ![arberg](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@arberg](https://discuss.kotlinlang.org/u/arberg)\ **Post date:** [September 8, 2020, 12:19pm UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/5 "2020-09-08T12:19:35Z")
Hi Francesco, Thank for you for your time and effort. I’ve created a sample project containing the error, attached as zip. EDIT: Man that’s bloody embarrasing. Apparently I didn’t read the error-message carefully and completely, and thus missed the nice detail that they added that told me exactly what to do. So all I have to do is enable structed keys, and I’m done. so problem solved. I’ll include the below, in case other’s drop by later, though. ========== My goal is to store my data on disk, and I have stored is as a map. In hindsight I see that I could have just stored is list, and moved to map after deserializing, but this was easier, and fit the bill at the time. I already have apps ‘out there’ with the old data format so in order to migrate to newer kotlin I have to somehow handle it. I get the following error ```auto Exception in thread "main" kotlinx.serialization.json.internal.JsonEncodingException: Value of type 'dk.MyTripId' can't be used in JSON as a key in the map. It should have either primitive or enum kind, but its kind is 'CLASS'. Use 'allowStructuredMapKeys = true' in 'Json {}' builder to convert such maps to [key1, value1, key2, value2,...] arrays. at kotlinx.serialization.json.internal.JsonExceptionsKt.InvalidKeyKindException(JsonExceptions.kt:67) at kotlinx.serialization.json.internal.WriteModeKt.switchMode(WriteMode.kt:58) at kotlinx.serialization.json.internal.StreamingJsonEncoder.beginStructure(StreamingJsonEncoder.kt:63) at kotlinx.serialization.encoding.Encoder$DefaultImpls.beginCollection(Encoding.kt:268) at kotlinx.serialization.json.JsonEncoder$DefaultImpls.beginCollection(JsonEncoder.kt) at kotlinx.serialization.json.internal.StreamingJsonEncoder.beginCollection(StreamingJsonEncoder.kt:15) at kotlinx.serialization.encoding.Encoder$DefaultImpls.beginCollection(Encoding.kt:257) at kotlinx.serialization.json.JsonEncoder$DefaultImpls.beginCollection(JsonEncoder.kt) at kotlinx.serialization.json.internal.StreamingJsonEncoder.beginCollection(StreamingJsonEncoder.kt:15) at kotlinx.serialization.internal.MapLikeSerializer.serialize(CollectionSerializers.kt:119) at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:223) at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:84) at dk.MyTripStorageData.write$Self(KotlinMigrationMain.kt:9) at dk.MyTripStorageData$$serializer.serialize(KotlinMigrationMain.kt) at dk.MyTripStorageData$$serializer.serialize(KotlinMigrationMain.kt:9) at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:223) at kotlinx.serialization.json.Json.encodeToString(Json.kt:73) at dk.KotlinMigrationMainKt.main(KotlinMigrationMain.kt:40) ``` This is my source code, the 1.3.72 version is outcommented below the 1.4.0 version: ```auto import kotlinx.serialization.Serializable import kotlinx.serialization.json.Json import kotlinx.serialization.json.JsonConfiguration @Serializable data class MyTripStorageData(val activeTripMap: MutableMap = mutableMapOf()) { fun add(trip: MyTripStateInfo) { activeTripMap[trip.tripId] = trip } operator fun get(tripId: MyTripId) = activeTripMap[tripId] } @Serializable data class MyTripId(val serverId: Int, val id: Long) @Serializable data class MyTripStateInfo( val tripId: MyTripId, val bookingName: String ) fun main(args: Array) { val tripId = MyTripId(1, 12L) val tripId2 = MyTripId(2, 14L) val data = MyTripStorageData() data.add(MyTripStateInfo(tripId, "Foo")) data.add(MyTripStateInfo(tripId2, "Bar")) // example lookup println(data[tripId]) // Simulate store my data on disk and restore on app-load // Kotlin 1.4 Version val ksonStorage: Json = Json { ignoreUnknownKeys = true; prettyPrint = true } val serializedData = ksonStorage.encodeToString(MyTripStorageData.serializer(), data) val decodedData = ksonStorage.decodeFromString(MyTripStorageData.serializer(), serializedData) // Kotlin 1.3.72 Version // val ksonStorage: Json = Json(JsonConfiguration.Stable.copy(ignoreUnknownKeys = true, prettyPrint = true)) // val serializedData = ksonStorage.stringify(MyTripStorageData.serializer(), data) // val decodedData = ksonStorage.parse(MyTripStorageData.serializer(), serializedData) println(serializedData) println(decodedData[tripId]) } ``` The serialized format by v 1.3.72 is ```auto { "activeTripMap": [ { "serverId": 1, "id": 12 }, { "tripId": { "serverId": 1, "id": 12 }, "bookingName": "Foo" }, { "serverId": 2, "id": 14 }, { "tripId": { "serverId": 2, "id": 14 }, "bookingName": "Bar" } ] } ``` [kotlin-test.zip](https://discuss.kotlinlang.org/uploads/short-url/wv4ICXamAJSk7m2pANmkb2lsrfJ.zip) (57.5 KB) ---
**Author:** ![fvasco](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/fvasco/32/1961_2.png) [@fvasco](https://discuss.kotlinlang.org/u/fvasco)\ **Post date:** [September 8, 2020, 12:42pm UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/6 "2020-09-08T12:42:40Z")
Ok @arberg, so you are using the `Json` format and you should use the `allowStructuredMapKeys`. You miss [this issue](https://github.com/Kotlin/kotlinx.serialization/issues/424) and [this pull request](https://github.com/Kotlin/kotlinx.serialization/pull/492). As suggested, you should set the `allowStructuredMapKeys` flag, ie: ```kotlin val ksonStorage: Json = Json { allowStructuredMapKeys = true; ignoreUnknownKeys = true; prettyPrint = true } ``` ---
**Author:** ![arberg](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@arberg](https://discuss.kotlinlang.org/u/arberg)\ **Post date:** [September 8, 2020, 6:44pm UTC](https://discuss.kotlinlang.org/t/kotlinx-serialization-how-to-migrate-map-from-0-20-0-to-1-0-m1-1-4-0-rc/19069/7 "2020-09-08T18:44:43Z")
> [@fvasco](#): > > allowStructuredMapKeys thank you for the links.