Realm migrations in Swift

问题

I have a Realm Object modeled as so

class WorkoutSet: Object {
     // Schema 0
     dynamic var exerciseName: String = ""
     dynamic var reps: Int = 0
     // Schema 0 + 1
     dynamic var setCount: Int = 0
}

I am trying to perform a migration.

Within my AppDelegate I have imported RealmSwift.

Within the function didFinishLaunchWithOptions I call

Migrations().checkSchema()

Migrations is a class declared in another file.

Within that file there is a struct declared as so.

func checkSchema() {
    Realm.Configuration(
        // Set the new schema version. This must be greater than the previously used
        // version (if you've never set a schema version before, the version is 0).
        schemaVersion: 1,

        // Set the block which will be called automatically when opening a Realm with
        // a schema version lower than the one set above
        migrationBlock: { migration, oldSchemaVersion in
            // We haven’t migrated anything yet, so oldSchemaVersion == 0
            switch oldSchemaVersion {
            case 1:
                break
            default:
                // Nothing to do!
                // Realm will automatically detect new properties and removed properties
                // And will update the schema on disk automatically
                self.zeroToOne(migration)
            }
    })
}

func zeroToOne(migration: Migration) {
    migration.enumerate(WorkoutSet.className()) {
        oldObject, newObject in
        let setCount = 1
        newObject!["setCount"] = setCount
    }
}

I am getting an error for adding setCount to the model

回答1:

You will need to invoke the migration. Merely creating a configuration, won't invoke it. There are two ways of doing this:

Set your configuration with migration as Realm's default configuration-

let config = Realm.Configuration(
  // Set the new schema version. This must be greater than the previously used
  // version (if you've never set a schema version before, the version is 0).
  schemaVersion: 1,

  // Set the block which will be called automatically when opening a Realm with
  // a schema version lower than the one set above
  migrationBlock: { migration, oldSchemaVersion in

    if oldSchemaVersion < 1 {
      migration.enumerate(WorkoutSet.className()) { oldObject, newObject in
        newObject?["setCount"] = setCount
      }    
    }
  }
) 
Realm.Configuration.defaultConfiguration = config

Migrate manually using migrateRealm :

migrateRealm(config)

Now your migration should work properly.

回答2:

Because you just create Realm.Configuration. Migration block is invoked by Realm if needed. You cannot invoke migration directly.

So to be invoke migration block, you should set configuration object to Realm, or set as default configuration. Then create Realm instance.

So You need to do the following:

let config = Realm.Configuration(
    // Set the new schema version. This must be greater than the previously used
    // version (if you've never set a schema version before, the version is 0).
    schemaVersion: 1,

    // Set the block which will be called automatically when opening a Realm with
    // a schema version lower than the one set above
    migrationBlock: { migration, oldSchemaVersion in
        // We haven’t migrated anything yet, so oldSchemaVersion == 0
        switch oldSchemaVersion {
        case 1:
            break
        default:
            // Nothing to do!
            // Realm will automatically detect new properties and removed properties
            // And will update the schema on disk automatically
            self.zeroToOne(migration)
        }
})

let realm = try! Realm(configuration: config) // Invoke migration block if needed

来源：https://stackoverflow.com/questions/34891743/realm-migrations-in-swift

标签

swift

migration

realm

data-migration

data-management