如何在应用程序开始运行代码之前运行迁移？

Question

我在一个快速的应用程序中使用realm.io.这是我第一次运行迁移,因为我有一个生产中的应用程序.我改变了其中一个模型并添加了几个额外的字段.

我按照文档中的示例进行操作,然后在不起作用的情况下引用了github repo的示例.我认为它可能比文档中的示例更加复杂.

这是我在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
    }

该print从来没有运行,我觉得很奇怪.我搞砸了什么？我假设我一定是.

以下是文档所说的内容,我不确定他们是否会遗漏某些东西:

// 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()

我有什么想法我做错了吗？

Answer 1

这最终成为解决方案。我不能说是我自己想出来的，因为我没有。我从 Realm 一位名叫 Claire 的优秀工程师那里得到了一些极好的帮助。

这是需要做的事情：

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。在 Claire 的建议下，Realm 被延迟加载（或尝试）并且构建数组的代码被移到 viewDidLoad 方法中，而之前在顶部调用它。

这允许领域迁移以提前运行。正如您可能想象的那样，老实说，我认为application在AppDelegate. 然而，我想我错了。

所以，这将解决它。如果您碰巧遇到同样的问题，请试一试。

更新：

下面是 appDelegate 函数现在的样子：

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
    }