RLMException, Migration is required for object type

I have an object NotSureItem in which I have three properties title whose name is renamed from text and textDescription which I had added later and a dateTime property. Now when I am going to run my app it crashes when I want to add something to these properties. It shows following statements.

'Migration is required for object type 'NotSureItem' due to the following errors:
- Property 'text' is missing from latest object model.
- Property 'title' has been added to latest object model.
- Property 'textDescription' has been added to latest object model.'

Here is my code:

import Foundation
import Realm

class NotSureItem: RLMObject {
    dynamic var title = ""   // renamed from 'text'
    dynamic var textDescription = "" // added afterwards
    dynamic var dateTime = NSDate()
}

Solution

As long as you have not released your app you can simply delete your app and run it again.

Everytime you change properties on your Realm objects your existing database becomes incompatible to the new one.

As long as you are still in the developing stage you can simply delete the app from the simulator / device and start it again.

Later when your app has been released and you change properties on your objects you have to implement a migration to the new database version.

To actually perform a migration you implement a Realm migration block. Typically you would add the block to application(application:didFinishLaunchingWithOptions:):

var configuration = Realm.Configuration(
    schemaVersion: 1,
    migrationBlock: { migration, oldSchemaVersion in
        if oldSchemaVersion < 1 {

            // if just the name of your model's property changed you can do this 
            migration.renameProperty(onType: NotSureItem.className(), from: "text", to: "title")

            // if you want to fill a new property with some values you have to enumerate
            // the existing objects and set the new value
            migration.enumerateObjects(ofType: NotSureItem.className()) { oldObject, newObject in
                let text = oldObject!["text"] as! String
                newObject!["textDescription"] = "The title is \(text)"
            }

            // if you added a new property or removed a property you don't
            // have to do anything because Realm automatically detects that
        }
    }
)
Realm.Configuration.defaultConfiguration = configuration

// opening the Realm file now makes sure that the migration is performed
let realm = try! Realm()

Whenever your scheme changes your have to increase the schemaVersion in the migration block and update the needed migration within the block.