How to migrate multiple realm files in one App

2018-06-12 04:29:12

I have two realm files in one App, something wrong when I wanna migrate them. I want realm update automatically when run in Xcode while does not change the schemaVersion every time.

class News: Object {
    @objc dynamic var name: String  
}

class NewsManager {
    static var realm = try! Realm()
    static var cacheRealm: Realm = {

        let documentDirectory = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask,
                                                         appropriateFor: nil, create: false)
        let url = documentDirectory.appendingPathComponent("cache.realm")
        var config = Realm.Configuration()
        config.fileURL = url
        return try! Realm(configuration: config)
    }()
}

When I add a new property to News such as @objc dynamic var title: String , I add the following code in AppDelegate func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool

let config = Realm.Configuration(schemaVersion: 1, migrationBlock: { migration, oldSchemaVersion in

    })
Realm.Configuration.defaultConfiguration = config

The message on crash at return try! Realm(configuration: config) in NewsManager .

Fatal error: 'try!' expression unexpectedly raised an error: Error Domain=io.realm Code=10 "Migration is required due to the following errors:
- Property 'News.test' has been added." UserInfo={Error Code=10, NSLocalizedDescription=Migration is required due to the following errors:
- Property 'News.test' has been added.}: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-900.0.69.2/src/swift/stdlib/public/core/ErrorType.swift, line 181

What should I do?

Realm: 3.0.1

Swift: 4.0

iOS : 10

Realm is working as expected. Some types of model changes Realm can migrate automatically, others require you to provide a manual migration. The one in your example is one of them.

Since you added a new, non-optional property of type String , Realm needs to go through all your existing models and figure out what to put in that property. If the property were type String? , it would make sense to use nil as a default value, and Realm could carry out the migration automatically. However, since the type is String and there's no obvious sensible default, Realm requires you to manually specify a value for the new property for each model object.

The right way to fix this "problem" is to increment your schema number and provide a migration block that actually specifies the new values for new properties whenever you change your model in a way that requires a migration.

Please review our documentation on migrations for more details.

Check it out https://realm.io/docs/swift/latest/#migrations. Realm site is very good for understanding how properly use Realm in your projects

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