如何在应用程序开始运行代码之前迁移到运行？

Question

我在 swift 应用中使用 realm.io。这是我第一次不得不运行迁移，因为我有一个应用程序正在生产中。我更改了其中一个模型并向其添加了几个额外的字段。

我按照文档中的示例进行操作，然后在不起作用时引用了 github 存储库的示例。我认为它可能比文档中的示例更复杂。

这是我的 appdelegate.swift 文件中的内容：

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

        print ("i'm in here")
        // Override point for customization after application launch.

        // Inside your application(application:didFinishLaunchingWithOptions:)

        window = UIWindow(frame: UIScreen.mainScreen().bounds)
        window?.rootViewController = UIViewController()
        window?.makeKeyAndVisible()

        // copy over old data files for migration
        let defaultPath = Realm.Configuration.defaultConfiguration.path!
        let defaultParentPath = (defaultPath as NSString).stringByDeletingLastPathComponent

        if let v0Path = bundlePath("default-v0.realm") {
            do {
                try NSFileManager.defaultManager().removeItemAtPath(defaultPath)
                try NSFileManager.defaultManager().copyItemAtPath(v0Path, toPath: defaultPath)
            } catch {}
        }

        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
                }
        })

        // define a migration block
        // you can define this inline, but we will reuse this to migrate realm files from multiple versions
        // to the most current version of our data model
        let migrationBlock: MigrationBlock = { migration, oldSchemaVersion in
            if oldSchemaVersion < 1 {

            }

            print("Migration complete.")
        }

        Realm.Configuration.defaultConfiguration = Realm.Configuration(schemaVersion: 1, migrationBlock: migrationBlock)

        // 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
        _ = try! Realm()


        return true
    }

print 从来没有运行我觉得奇怪。我搞砸了吗？我想我一定是。

文档是这样说的，我不确定他们是否遗漏了什么：

// 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) {
      // 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 realm = try! Realm()

知道我做错了什么吗？

Answer 1

看起来您 flat-out 将代码从 Realm Swift 'Migration' 示例中复制出来并逐字粘贴。很多代码实际上是 'set-up' 每次示例应用运行时进行新的演示迁移，而对于正常的 Realm 迁移实际上不是必需的。

领域迁移有两个组成部分：

增加 Configuration 对象中的模式版本号。 Realm 文件从版本 0 开始，每次要进行新迁移时，将其增加 1。
提供一个迁移块，它将针对您的 Realm 架构版本的每个增量执行多次。虽然块本身是必需的，但它的目的是让您 copy/transform 旧 Realm 文件中的任何数据。如果您只是简单地添加新字段，您可以将该块留空。

如果您的 UIViewController 在其实现中完全使用 Realm，最好将您的迁移代码放在 UIWindow 代码之前，以确保迁移已经在 UIViewController 之前发生开始使用它（否则你会得到一个例外）。

由于您所做的只是向其中添加几个字段，因此这就是您需要的全部代码：

let migrationBlock: MigrationBlock = { migration, oldSchemaVersion in
    //Leave the block empty
}
Realm.Configuration.defaultConfiguration = Realm.Configuration(schemaVersion: 1, migrationBlock: migrationBlock)

window = UIWindow(frame: UIScreen.mainScreen().bounds)
window?.rootViewController = UIViewController()
window?.makeKeyAndVisible()

Answer 2

这按预期工作，在降级时抛出异常（如果使用版本不同的分支）等。还显示了一些示例迁移。

    Realm.Configuration.defaultConfiguration = Realm.Configuration(
        // Update this number for each change to the schema.
        schemaVersion: 4,
        migrationBlock: { migration, oldSchemaVersion in
            if oldSchemaVersion < 2 {
                migration.enumerate(SomeObject.className()) { oldObject, newObject in
                    newObject!["newColumn"] = Enum.Unknown.rawValue
                }
            }
            if oldSchemaVersion < 3 {
                migration.enumerate(SomeOtherObject.className()) { oldObject, newObject in
                    newObject!["defaultCreationDate"] = NSDate(timeIntervalSince1970: 0)
                }
            }
            if oldSchemaVersion < 4 {
                migration.enumerate(SomeObject.className()) { oldObject, newObject in
                    // No-op.
                    // dynamic properties are defaulting the new column to true
                    // but the migration block is still needed
                }
            }
    })

显然不会像 SomeObject 等那样编译，但你明白了:)

Answer 3

这最终成为了解决方案。我不能说我自己想出了它，因为我没有。我从 realm 的一位名叫克莱尔的出色工程师那里得到了一些极好的帮助。

以下是需要完成的工作：

class RoomsViewController: UIViewController, UITableViewDelegate {

    var activeRoom = -1
    var room: Room? = nil
    var array = [Room]()

    lazy var realm:Realm = {
        return try! Realm()
    }()


    var notificationToken: NotificationToken?

    @IBOutlet weak var roomsTable: UITableView!

    override func viewDidLoad() {
        super.viewDidLoad()

        array = Array(realm.objects(Room.self))

        setupUI()
        // Set realm notification block
        notificationToken = realm.addNotificationBlock { [unowned self] note, realm in
            // TODO: you are going to need to update array
            self.roomsTable.reloadData()
        }
    }

这是第一个加载的视图控制器，它立即查询领域数据库以构建数组。根据 Claire 的建议，Realm 被延迟加载（或尝试过）并且构建数组的代码被移动到 viewDidLoad 方法中，而之前它在顶部被调用。

这使得领域可以提前迁移到运行。正如您可能想象的那样，老实说，我假设在 AppDelegate 中加载 application 函数之后才加载视图。然而，我想我错了。

所以，这将解决它。如果您碰巧运行遇到同样的问题，请试一试。

更新：

appDelegate 函数现在是这样的：

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

        // 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) {
                    migration.enumerate(Inventory.className()) { oldObject, newObject in
                        // No-op.
                        // dynamic properties are defaulting the new column to true
                        // but the migration block is still needed
                    }
                    migration.enumerate(Profile.className()) { oldObject, newObject in
                        // No-op.
                        // dynamic properties are defaulting the new column to true
                        // but the migration block is still needed
                    }
                    migration.enumerate(Room.className()) { oldObject, newObject in
                        // No-op.
                        // dynamic properties are defaulting the new column to true
                        // but the migration block is still needed
                    }
                    migration.enumerate(Box.className()) { oldObject, newObject in
                        // No-op.
                        // dynamic properties are defaulting the new column to true
                        // but the migration block is still needed
                    }
                }
        })

        // 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
        do {
            _ = try Realm()
        } catch let _ as NSError {
            // print error
        }


        return true
    }

Answer 4

我发现这在视图控制器中效果最好：

let migrationBlock: MigrationBlock = { migration, oldSchemaVersion in
    //Leave the block empty
}

lazy var realm:Realm = {
    Realm.Configuration.defaultConfiguration = Realm.Configuration(schemaVersion: 1, migrationBlock: migrationBlock)
    return try! Realm()
}()

换句话说，将配置分配移动到块中，以免执行得太晚。

如何在应用程序开始运行代码之前迁移到运行？

How can I get the migration to run before the app starts to run the code?

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如何在应用程序开始 运行 代码之前迁移到 运行？

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如何在应用程序开始运行代码之前迁移到运行？