RLMException，对象类型需要迁移

Question

我有一个对象NotSureItem，其中我有三个属性title，其名称从text 和textDescription 重命名，我后来添加了一个dateTime 属性。现在，当我要运行我的应用程序时，当我想向这些属性添加一些东西时它会崩溃。它显示以下语句。

'Migration is required for object type 'NotSureItem' due to the following errors:
- Property 'text' is missing from latest object model.
- Property 'title' has been added to latest object model.
- Property 'textDescription' has been added to latest object model.'

这是我的代码：

import Foundation
import Realm

class NotSureItem: RLMObject {
    dynamic var title = ""   // renamed from 'text'
    dynamic var textDescription = "" // added afterwards
    dynamic var dateTime = NSDate()
}

Answer 1

如果您在增加 schemaVersion 后仍收到此错误。然后进行仔细检查。是否在更新 App Delegate 中的架构版本之前调用任何 Realm 对象。

在我的例子中，我试图在执行代码迁移语句之前访问 App Delegate 中的领域对象。

始终将迁移代码写在 App Delegate (DidfinishLaunchingWithOptions) 的第一行，这样更安全。

Answer 2

只要您尚未发布您的应用，您只需删除您的应用并重新运行即可。

每次更改 Realm 对象的属性时，现有数据库都会与新数据库不兼容。

只要您仍处于开发阶段，您只需从模拟器/设备中删除应用程序并重新启动即可。

当您的应用发布后并且您更改对象的属性时，您必须迁移到新的数据库版本。

要实际执行迁移，您需要实现一个 Realm 迁移块。通常你会将该块添加到application(application:didFinishLaunchingWithOptions:):

var configuration = Realm.Configuration(
    schemaVersion: 1,
    migrationBlock: { migration, oldSchemaVersion in
        if oldSchemaVersion < 1 {

            // if just the name of your model's property changed you can do this 
            migration.renameProperty(onType: NotSureItem.className(), from: "text", to: "title")

            // if you want to fill a new property with some values you have to enumerate
            // the existing objects and set the new value
            migration.enumerateObjects(ofType: NotSureItem.className()) { oldObject, newObject in
                let text = oldObject!["text"] as! String
                newObject!["textDescription"] = "The title is \(text)"
            }

            // if you added a new property or removed a property you don't
            // have to do anything because Realm automatically detects that
        }
    }
)
Realm.Configuration.defaultConfiguration = configuration

// opening the Realm file now makes sure that the migration is performed
let realm = try! Realm()

每当您的方案更改时，您必须在迁移块中增加schemaVersion 并在块内更新所需的迁移。

Answer 3

只需增加架构版本

Realm 会自动检测新属性和移除的属性

var 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: 2,
            
            // 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) {
                    // Nothing to do!
                    // Realm will automatically detect new properties and removed properties
                    // And will update the schema on disk automatically
                }
        })
        
               
        do{
            realm = try Realm(configuration: config)
            
            print("Database Path : \(config.fileURL!)")
        }catch{
            print(error.localizedDescription)
        }

Answer 4

删除应用并重新安装不是一个好习惯。从我们第一次遇到迁移需求开始，我们就应该在开发过程中加入一些迁移步骤。 SilentDirge 给出的链接很好：realm migration document，它为处理不同情况提供了很好的例子。

对于最小迁移任务，上面链接中的以下代码 sn -p 可以自动执行迁移，并与 AppDelegate 的 disFinishLaunchWithOptions 方法一起使用：

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) {
      // Nothing to do!
      // Realm will automatically detect new properties and removed properties
      // And will update the schema on disk automatically
    }
  })

// 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 _ = try! Realm()

Answer 5

您可以像这样在启动时擦除数据库：

[[NSFileManager defaultManager] removeItemAtURL:[RLMRealmConfiguration defaultConfiguration].fileURL error:nil];

Answer 6

您修改后的数据库不再与保存的数据库兼容，这就是需要迁移的原因。您的选择是删除旧的数据库文件并重新开始（如果您处于初始开发阶段，效果很好），或者如果您在现场，请进行迁移。

您可以通过定义架构版本并在您的 Realm 配置中提供数据库迁移“脚本”来实现此目的。整个过程记录在这里（连同代码示例）：here

Answer 7

下面的代码对我有用

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{  
RLMRealmConfiguration *config = [RLMRealmConfiguration    defaultConfiguration];
 config.schemaVersion = 2;
config.migrationBlock = ^(RLMMigration *migration, uint64_t  oldSchemaVersion) {
  // The enumerateObjects:block: method iterates
  // over every 'Person' object stored in the Realm file
  [migration enumerateObjects:Person.className
                    block:^(RLMObject *oldObject, RLMObject *newObject) {
    // Add the 'fullName' property only to Realms with a schema version of 0
    if (oldSchemaVersion < 1) {
      newObject[@"fullName"] = [NSString stringWithFormat:@"%@ %@",
                            oldObject[@"firstName"],
                            oldObject[@"lastName"]];
    }

    // Add the 'email' property to Realms with a schema version of 0 or 1
    if (oldSchemaVersion < 2) {
     newObject[@"email"] = @"";
    }
  }];
 };
[RLMRealmConfiguration setDefaultConfiguration:config];

// now that we have updated the schema version and provided a migration block,
// opening an outdated Realm will automatically perform the migration and
// opening the Realm will succeed
[RLMRealm defaultRealm];

return YES;
}

更多信息：https://realm.io/docs/objc/latest/#getting-started