Swift：如何迁移自定义领域

Question

我正在尝试对我的自定义领域文件进行迁移。请注意，在这个项目中，我在默认领域文件之上有两个自定义领域文件，一个 Photo.realm 和一个 Transport.realm。我在 Photo 对象中添加了一个新属性，如下所示：

class Photo: Object {
    @objc dynamic var id: String? = nil
    @objc dynamic var secret: String? = nil
    @objc dynamic var server: String? = nil
    @objc dynamic var farm: Int = 0
    @objc dynamic var imageData: Data? = nil
    @objc dynamic var tranport: Transport? //Newly added attribute
}

并且想迁移。我已经阅读了文档，并且由于我正在迁移自定义领域文件，因此我修改了代码并将它们添加到 didFinishLaunchingWithOptions，如下所示：

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

    let defaultConfig = Realm.Configuration()

    if let fileURL = defaultConfig.fileURL {
        let photoRealmFileURL = fileURL.deletingLastPathComponent().appendingPathComponent("Photo.realm")
        let photoMigrationConfig = Realm.Configuration(fileURL: photoRealmFileURL, schemaVersion: 1, migrationBlock: { (migration, oldSchemaVersion) in
            if (oldSchemaVersion < 1) {

            }
        }, objectTypes: [Photo.self])

        do {
            let _ = try Realm(configuration: photoMigrationConfig)
        } catch let error {
            print("Migration Error", error.localizedDescription)
        }

    }

    return true
}

在我的 HomeController 中，我像这样启动我的领域：

class HomeController: UICollectionViewController {

    var photoRealm = try! Realm()
    var transportRealm = try! Realm()

    override func viewDidLoad() {
        super.viewDidLoad()

        setupRealm()
    }

    fileprivate func setupRealm() {
        let defaultConfig = Realm.Configuration()

        if let fileURL = defaultConfig.fileURL {
            let photoRealmFileURL = fileURL.deletingLastPathComponent().appendingPathComponent("Photo.realm")
            let photoConfig = Realm.Configuration(fileURL: photoRealmFileURL, objectTypes: [Photo.self])

            let transportRealmFileURL = fileURL.deletingLastPathComponent().appendingPathComponent("Transport.realm")
            let tranportConfig = Realm.Configuration(fileURL: transportRealmFileURL, objectTypes: [Transport.self])

            do {
                photoRealm = try Realm(configuration: photoConfig)
                transportRealm = try Realm(configuration: tranportConfig)

                let cars = Transport()
                cars.name = "cars"

                let planes = Transport()
                planes.name = "planes"

                try transportRealm.write {
                    transportRealm.add(cars)
                    transportRealm.add(planes)
                }

            } catch let error {
                print("Error setting Realm", error.localizedDescription)
            }
        }
    }

有了这个，我被抛出了错误：

线程 1：致命错误：“尝试！”表达式意外引发错误： Error Domain=io.realm Code=10 "需要迁移，因为 以下错误： - 属性 'Photo.tranport' 已添加。" UserInfo={NSLocalizedDescription=迁移是必需的，因为 以下错误： - 已添加属性“Photo.tranport”。错误代码=10}

我想很明显迁移没有正确完成。由于我正在迁移自定义领域而不是默认领域，因此文档不太清楚如何正确执行此操作。

Answer 1

您可以通过检查要更新的架构版本来迁移您的领域数据库。并将配置传递给默认值 领域的配置。

将这些代码行添加到您的 appDelegate 的 didFinishLaunchingWithOptions 方法中。在您的领域配置之后并对其进行必要的更改。

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 {
     // Add your class name where you have added new property 'tranport'.
      migration.enumerate(Photo.className()) { oldObject, newObject in
        newObject?["tranport"] = "Your value"
      }    
    }
  }
) 
Realm.Configuration.defaultConfiguration = config