Hi all! I googled quite a lot and read https://www.hackingwithswift.com/quick-start/swiftdata/how-to-create-a-complex-migration-using-versionedschema again, but I still can not find a way to change the data type of a class, e.g.

from

@Model
final class Race {
    var timestamp: Date = Date()

    var cc: Int = 150
}

to

@Model
final class Race {
    var timestamp: Date = Date()

    var cc: String = "150"
}

what should I fill in willMigrate block?

static let migrateV1toV2 = MigrationStage.custom(
    fromVersion: RacesSchemaV1.self,
    toVersion: RacesSchemaV2.self,
    willMigrate: { context in
        let items = try? context.fetch(FetchDescriptor<RacesSchemaV1.Race>())

         // TODO: what to do to change the type of cc?

        try? context.save()
    }, didMigrate: nil
)

Thanks in advance!

Not 100% sure if this is the best way and if it works but try something like that. Apologies for any typos as code added right here :)

static var itemsToMigrate: [Race] = []

static let migrateV1toV2 = MigrationStage.custom(
    fromVersion: RacesSchemaV1.self,
    toVersion: RacesSchemaV2.self,
    willMigrate: { context in
    // so you take all your items from old version
        itemsToMigrate = try? context.fetch(FetchDescriptor<RacesSchemaV1.Race>())
    }, didMigrate { context in
      // loop through the items in old version, take each item cc info and add to updated version and converting it to String.
        for item in itemsToMigrate {
          context.insert(RacesSchemaV2.Race(cc: String(item.cc))) // for safety may be add check for type conversion to String...
        }

        try? context.save()
  }
)