只需递增架构版本

Question

我有一个对象NotSureItem，其中我有三个属性title，其名称已从text重新命名，textDescription我稍后添加了dateTime属性。现在，当我要运行我的应用程序时，它会在我想要向这些属性添加内容时崩溃。它显示以下陈述。

'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

只要您尚未发布应用，就可以删除自己的应用并再次运行。

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。

只要您还处于开发阶段，您只需从模拟器/设备中删除该应用程序，然后重新启动即可。

稍后当您的应用已发布并且您更改了对象的属性时，您必须实现向新数据库版本的迁移。

要实际执行迁移，您需要实现Realm迁移块。通常，您会将块添加到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()

每当您的方案发生变化时，您必须增加迁移块中的schemaVersion并更新块中所需的迁移。

Answer 2

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，上述链接中的以下代码段可以自动执行迁移，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 3

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

Answer 4

您修改的数据库不再与已保存的数据库兼容，这就是需要迁移的原因。您可以选择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，则效果很好），或者如果您还在，请进行迁移。

您可以通过定义架构版本并提供数据库迁移＆＃39;脚本来实现此目的。在您的Realm配置中。这里记录了整个过程（以及代码示例）：here

Answer 5

您可以在启动时删除数据库，如下所示：

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

Answer 6

只需递增架构版本

Realm将自动检测新属性并删除属性

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 7

如果即使在递增schemaVersion后也遇到此错误。然后进行仔细检查。在更新App Delegate中的架构版本之前，是否您正在调用任何Realm对象。

对于我来说，我试图在执行该代码迁移语句之前访问App Delegate中的Realm对象。

始终将迁移代码写在App Delegate的第一行（DidfinishLaunchingWithOptions）中，以确保安全。

RLMException，对象类型需要迁移

7 个答案:

只需递增架构版本

Realm将自动检测新属性并删除属性