9. Migrasi Schema

Setiap kali schema berubah (tambah properti, ubah nama, hapus model), SwiftData harus diberitahu agar bisa memigrasikan data lama.

Lightweight Migration (Otomatis)

Untuk perubahan sederhana — menambah properti opsional atau dengan default value — SwiftData dapat memigrasi secara otomatis tanpa konfigurasi tambahan:

swift
// v1: model awal
@Model final class Item {
    var name: String
    init(name: String) { self.name = name }
}

// v2: tambah properti dengan default — lightweight migration otomatis
@Model final class Item {
    var name: String
    var createdAt: Date = Date()   // default value → safe untuk migrate
    var notes: String?              // optional → safe untuk migrate
    init(name: String) { self.name = name }
}

Custom Migration dengan VersionedSchema

Untuk perubahan yang lebih kompleks (rename properti, ubah tipe, hapus dan re-create relasi):

swift
// MARK: - Schema Versions

enum AppSchema: VersionedSchema {
    static var versionIdentifier = Schema.Version(1, 0, 0)
    static var models: [any PersistentModel.Type] { [AppSchema.Task.self] }

    @Model
    final class Task {
        var title: String
        var done: Bool  // nama lama

        init(title: String) {
            self.title = title
            self.done = false
        }
    }
}

enum AppSchemaV2: VersionedSchema {
    static var versionIdentifier = Schema.Version(2, 0, 0)
    static var models: [any PersistentModel.Type] { [AppSchemaV2.Task.self] }

    @Model
    final class Task {
        var title: String
        var isCompleted: Bool  // nama baru — perlu custom migration
        var priority: Int

        init(title: String) {
            self.title = title
            self.isCompleted = false
            self.priority = 0
        }
    }
}

// MARK: - Migration Plan

enum AppMigrationPlan: SchemaMigrationPlan {
    static var schemas: [any VersionedSchema.Type] {
        [AppSchema.self, AppSchemaV2.self]
    }

    static var stages: [MigrationStage] {
        [migrateV1toV2]
    }

    static let migrateV1toV2 = MigrationStage.custom(
        fromVersion: AppSchema.self,
        toVersion: AppSchemaV2.self,
        willMigrate: nil,
        didMigrate: { context in
            // Setelah migrasi struktural selesai, migrasikan data
            let descriptor = FetchDescriptor<AppSchemaV2.Task>()
            let tasks = try context.fetch(descriptor)
            // isCompleted sudah di-set dari 'done' oleh Core Data migration engine
            // karena kita register mapping di originalName
            try context.save()
        }
    )
}

// MARK: - Penggunaan di App

@main
struct MyApp: App {
    let container: ModelContainer

    init() {
        do {
            container = try ModelContainer(
                for: AppSchemaV2.Task.self,
                migrationPlan: AppMigrationPlan.self
            )
        } catch {
            fatalError("Failed to create container: \(error)")
        }
    }

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(container)
    }
}