How to Avoid Migration in Realmswift

How can I avoid migration in RealmSwift

There are two ways to skip migration error regardless schema changes.

1. Use deleteRealmIfMigrationNeeded property. If it is true, recreate the Realm file with the provided schema if a migration is required.

   let config = Realm.Configuration(deleteRealmIfMigrationNeeded: true)
   Realm.Configuration.defaultConfiguration = config
   
   let realm = try! Realm()
   ...
   

   　　

2. Increment schema version every launch. Realm has auto migration feature. If you don't need to migrate existing data, you can just increment schema version. Schema will be changed by Realm automatically.

   let config = Realm.Configuration(schemaVersion: try! schemaVersionAtURL(Realm.Configuration.defaultConfiguration.fileURL!) + 1)
   Realm.Configuration.defaultConfiguration = config
   
   let realm = try! Realm()
   ...
   

Unable to do a Realm migration in Swift

This exception will be thrown when stored data doesn’t match the model you have in code.

You shouldn’t need to do anything in the migration block, however you will need to trigger a migration by updating the value of Realm.Configuration.schemaVersion, e.g.:

schemaVersion: 3,

Realm Migration: Migrating objects to another

You don't need to do anything with LinkingObjects, realm calculates those automatically when you query them.

All you'll need to do in your migration is set media to be a new Media object with the values you already have.

Other notes:

• The second enumerateObjects isn't needed.
• You can remove image, coverImage, and video from Item since you're moving those value to Media

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Edit: This is what you would need to have in your migration.

let media = Media()
media.fullImage = oldItem?["image"] as! String
media.thumbnailImage = oldItem?["coverImage"] as! String
media.video = oldItem?["video"] as! String

newItem?["media"] = media

How to keep certain changed properties unchanged in Realm migration - Swift

I figured it out. You have to do a partial serialization.

Changed this:

realm.add(thing, update: .modified)

To:

realm.create(Thing.self, value: [
   "id": thing.id,
   "propertyOne": thing.propertyOne
   // Leave out propertyTwo to leave it unchanged
], update: .modified)

Understanding migrations in Realm - Swift

No, in this case you don't need to perform a migration. You only need to perform a migration in case existing objects need to be changed (adding/removing properties of existing Realm model classes).

If you add a new class to Realm, you don't need to perform a migration.

In most cases, Realm can automatically perform the migration and all you need to do is increase your schema version by 1. However, if you are for example combining two existing properties into a new one, you need to handle that manually in your migration block.

Detect if Realm.io db needs migration - if so, destroy it

This has been working like a charm for me since Swift 2 introduced try/catch. I just call testRealmFile() from my app delegate at launch, and all is cool after that.

func testRealmFile(){
    do {
        try Realm().objects(Model1)
        try Realm().objects(Model2)
    } catch {
        print("can't access realm, migration needed")
        deleteRealmFile()
    }
}
func deleteRealmFile(){
    if let path = Realm.Configuration.defaultConfiguration.path {
        do{
            try NSFileManager.defaultManager().removeItemAtPath(path)
            print("realm file deleted")
        } catch {
            print("no realm file to delete")
        }
    }
}

Swift Realm migration create reference from old type to new one

After long testing and trying different possibilities I managed to migrate the data.
Here is what I did to accomplish this.

I used this as a base:

class RealmMigrationObject {
    let migration: () -> ()

    init(migration: @escaping () -> ()) {
        self.migration = migration
    }
}

and derived classes from that. Something like:

class MigrationObjectToThree: RealmMigrationObject {

    init() {
        super.init(migration: MigrationObjectToThree.migration)
    }

    private static func migration() {
        print("Migration to three | migration")

        var imageInfos:   [ImageInfo]      = []

        let config = Realm.Configuration(schemaVersion: 3, migrationBlock: { migration, oldSchemaVersion in

            print("Migration to three | migrationBlock")
            print("RealmMigration: Applying migration from \(oldSchemaVersion) to 3")

            migration.deleteData(forType: "ExploreSectionObjectRealm")

            migration.enumerateObjects(ofType: "ImageInfoRealm") { oldInfo, newObject in
                guard let oldInfo = oldInfo else {
                    return
                }

                guard let id = oldInfo["id"] as? String,
                      let url = oldInfo["url"] as? String,
                      let url500 = oldInfo["url500"] as? String,
                      let url400 = oldInfo["url400"] as? String,
                      let url300 = oldInfo["url300"] as? String,
                      let url200 = oldInfo["url200"] as? String,
                      let url100 = oldInfo["url100"] as? String,
                      let colorString = oldInfo["color"] as? String,
                      let color = UIColor(hexString: colorString) else {
                    return
                }
                imageInfos.append(ImageInfo(id: id,
                                            url: url,
                                            url500: url500,
                                            url400: url400,
                                            url300: url300,
                                            url200: url200,
                                            url100: url100,
                                            color: color))
            }

        })

        Realm.Configuration.defaultConfiguration = config
        do {
            let realm = try Realm(configuration: config)
        print("Realm is located at: \(realm.configuration.fileURL?.description ?? "")")
            print(realm.configuration.fileURL?.description ?? "") // Printing here on purpose  as it's easier to copy
        } catch {
        print("Realm Error: \(error), trying to rebuild realm from scratch")

            let deleteMigrationConfig = Realm.Configuration(schemaVersion: RealmHelper.schemaVersion,
                                                            deleteRealmIfMigrationNeeded: true)
            do {
                _ = try Realm(configuration: deleteMigrationConfig)
            } catch {
                print("Failed to instantiate: \(error.localizedDescription)")
            }
        }

        RealmHelper.removeRealmFiles()
        Realm.Configuration.defaultConfiguration = Realm.Configuration(schemaVersion: 3)

        imageInfos.forEach({ $0.save() })
    }
}

From that I just created all migration for the difference between the current schema version and target schema version on looped over all migrations simply executing the migration function of that given object.

Realm migration not called

If you write let realm = try! Realm() in a view controller as an instance variable, it will be called before application: didFinishLaunchingWithOptions from Storyboard. To resolve this, you can use lazy var realm = try! Realm() instead. lazy defers creating an instance variable until the variable is accessed.

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