I am trying to convert a string field to an integer field in our database schema. However, the custom migration that I write doesn't seem to run. My Model //Run 1 //typealias Book = BookSchemaV1.Book //Run 2 typealias Book = BookSchemaV2.Book // MARK: - Migration Plan enum BookModelMigrationPlan: SchemaMigrationPlan { static var schemas: [any VersionedSchema.Type] = [ BookSchemaV1.self, BookSchemaV2.self ] static var stages: [MigrationStage] = [migrateV1toV2] static var oldBooks: [BookSchemaV1.Book] = [] static let migrateV1toV2 = MigrationStage.custom( fromVersion: BookSchemaV1.self, toVersion: BookSchemaV2.self, willMigrate: nil, didMigrate: { context in oldBooks = try context.fetch(FetchDescriptor<BookSchemaV1.Book>()) oldBooks.forEach { oldBook in do { let newBook = BookSchemaV2.Book( bookID: String(oldBook.bookID), title: oldBook.title ) context.insert(newBook) context.delete(oldBook) try context.save() } catch { print("New model not saved") } } } ) } // MARK: - Schema Versions enum BookSchemaV1: VersionedSchema { static var models: [any PersistentModel.Type] = [Book.self] static var versionIdentifier = Schema.Version(1, 0, 0) @Model final class Book { @Attribute(.unique) var bookID: Int var title: String init( bookID: Int, title: String ) { self.bookID = bookID self.title = title } } } enum BookSchemaV2: VersionedSchema { static var models: [any PersistentModel.Type] = [Book.self] static var versionIdentifier = Schema.Version(2, 0, 0) @Model class Book { @Attribute(.unique) var bookID: String var title: String init( bookID: String, title: String ) { self.bookID = bookID self.title = title } } } @MainActor class AppDataContainer { static let shared = AppDataContainer() let container: ModelContainer private init() { do { let schema = Schema([Book.self]) let config = ModelConfiguration(schema: schema) container = try ModelContainer(for: schema, migrationPlan: BookModelMigrationPlan.self, configurations: [config]) } catch { fatalError("Could not create ModelContainer: \(error)") } } }