Lesson 12 - iOS ToDo app in Swift - Database migrations and sorting

In the previous lesson, iOS ToDo app in Swift - Custom TableViewCell, we added task priorities to our ToDo app in Swift for iOS.

We promised to perform database migrations and learn to sort data in today's iOS development tutorial.

Realm migrations

To migrate a database basically means to modify the database schema to correspond to the new model. It's easy to do it in Realm, we just create a code block in AppDelegate, specifically in the following method:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool

Realm has a cool documentation where we can find everything needed. Our migration will look like this:

Realm.Configuration.defaultConfiguration = Realm.Configuration(
            schemaVersion: 1,
            migrationBlock: { migration, oldSchemaVersion in
                if (oldSchemaVersion < 1) {
                    migration.enumerateObjects(ofType: ToDo.className()) { oldObject, newObject in
                        newObject!["priority"] = 1

We'll place this whole block to the


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Article description

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We'll learn to migrate databases of iOS apps which are already in AppStore. And also to sort and filter data (our objects) using Realm in Swift.

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Article has been written for you by Filip Němeček