如何更改类的属性，而不必使用领域删除应用程序

Question

目前，我正在用Swift编写一个使用领域的程序。我对iOS开发相当陌生，但我对领域的理解是，当您更改存储在领域中的类时，需要从设备中删除应用程序，以摆脱持久化数据。不幸的是，我已经手动输入了一个相当大的数据库到应用程序。

目前，我需要在类中更改属性的名称，但将来可能需要添加属性。更新领域存储的最佳方法是什么，这样我就不需要删除应用程序了？

这是我的模型之一：

class Device: Object {

   dynamic var name = ""
   dynamic var id = ""
   dynamic var os = ""
   dynamic var currentUser: User?
   dynamic var dateStamp = NSDate()
}

Answer 1

您可以添加一个迁移，如我们的医生中所示，并使用它来接管新属性的旧值：

Objective-C

// Inside your [AppDelegate didFinishLaunchingWithOptions:]

RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
// 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).
config.schemaVersion = 1;

// Set the block which will be called automatically when opening a Realm with a
// schema version lower than the one set above
config.migrationBlock = ^(RLMMigration *migration, uint64_t oldSchemaVersion) {
    // We haven’t migrated anything yet, so oldSchemaVersion == 0
    if (oldSchemaVersion < 1) {
        // The -enumerateObjects:block: method iterates
        // over every Device object stored in the Realm file
        [migration enumerateObjects:Device.className
                      block:^(RLMObject *oldObject, RLMObject *newObject) {
            // e.g. Rename 'os' to 'operatingSystem'
            newObject[@"operatingSystem"] = oldObject[@"os"]
        }];
    }
};

// Tell Realm to use this new configuration object for the default Realm
[RLMRealmConfiguration setDefaultConfiguration:config];

// Now that we've told Realm how to handle the schema change, opening the file
// will automatically perform the migration
[RLMRealm defaultRealm];

斯威夫特(与王国斯威夫特)

https://realm.io/docs/swift/latest/#performing-a-migration

// Inside your application(application:didFinishLaunchingWithOptions:)

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
    if (oldSchemaVersion < 1) {
        // The enumerate(_:_:) method iterates
        // over every Device object stored in the Realm file
        migration.enumerate(Device.className()) { oldObject, newObject in
            // e.g. Rename 'os' to 'operatingSystem'
            newObject["operatingSystem"] = oldObject["os"]
        }
    }
  })

// Tell Realm to use this new configuration object for the default Realm
Realm.Configuration.defaultConfiguration = config

// Now that we've told Realm how to handle the schema change, opening the file
// will automatically perform the migration
let realm = try! Realm()