ios - Swift Realm 迁移创建从旧类型到新类型的引用

Question

最初我有以下类(class):

@objcMembers public class NormalObjectRealm: Object {

    // Shared
    dynamic public var id:                String?
    dynamic public var title:             String?
    dynamic public var subTitle:          String?
    dynamic public var imageInfo:         ImageInfoRealm?
    dynamic public var descriptionString: String?
    public var categories = List<String>()
    public var count    = RealmOptional<Int>()
    public var episodes = List<String>()


    public static let realmPrimaryKey: String = "id"

    public override class func primaryKey() -> String? {
        return NormalObjectRealm.realmPrimaryKey
    }
}

@objcMembers public class ImageInfoRealm: Object {

    dynamic public var id: String?
    dynamic public var url:    String?

    public static let realmPrimaryKey: String = "id"

    public override class func primaryKey() -> String? {
        return ImageInfoRealm.realmPrimaryKey
    }

}

但是现在 NormalObjectRealm 被合并到一个新类中，如下所示:

@objcMembers public class MediaObjectRealm: Object {

    // Shared
    dynamic public var id:                String?
    dynamic public var title:             String?
    dynamic public var subTitle:          String?
    dynamic public var imageInfo:         ImageInfoRealm?
    dynamic public var descriptionString: String?
    public var categories = List<String>()
    dynamic public var type: String?

    // NormalObjectRealm
    public var episodeCount    = RealmOptional<Int>()
    public var episodes = List<String>()

    // OtherObjectRealm
    dynamic public var urlOne:    String?
    dynamic public var urlTwo: String?
    dynamic public var urlThree:   String?
    public var isExplicit = RealmOptional<Bool>()

    public static let realmPrimaryKey: String = "id"

    public override class func primaryKey() -> String? {
        return MediaObjectRealm.realmPrimaryKey
    }
}

我目前正在尝试在此处编写转换的迁移，其基本想法是将大部分字段从 NormalObjectRealm 转移到 MediaObjectRealm。

这就是我的迁移 block 当前的样子

Realm.Configuration(schemaVersion: schemaVersion, migrationBlock: { migration, oldSchemaVersion in
            if oldSchemaVersion < temp {
                print("RealmMigration: Applying migration from \(oldSchemaVersion) to \(temp)")

                migration.enumerateObjects(ofType: "NormalObjectRealm") { oldObject, newObject in
                    guard let oldObject = oldObject else {
                        return
                    }
                    guard let id = oldObject["id"] as? String else {
                        return
                    }
                    guard let title = oldObject["title"] as? String else {
                        return
                    }

                    guard let subTitle = oldObject["subTitle"] as? String else {
                        return
                    }

                    guard let imgInfo = oldObject["imageInfo"] else {
                        return
                    }
                    guard let count = oldObject["count"] as? RealmOptional<Int>? else {
                        return
                    }

                    guard let descriptionString = oldObject["descriptionString"] as? String? else {
                        return
                    }

                    let item = migration.create("MediaObjectRealm")
                    item["id"] = id
                    item["title"] = title
                    item["subTitle"] = subTitle
                    item["descriptionString"] = descriptionString
                    item["type"] = "myType"
                    item["episodeCount"] = episodeCount // Doesn't work either...

                    migration.enumerateObjects(ofType: "ImageInfoRealm") { oldImg, newImg in
                        guard let oldImg = oldImg else {
                            return
                        }

                        let inf = oldObject.value(forKey: "imageInfo")
                        print(inf)
                        let t = migration.create("ImageInfoRealm", value: inf)
                        print("doing it")
                        //                      print(t)
                        item.setValue(t, forKey: "imageInfo")

                    }
                }
            }
    })

id、title、subTitle 等(字符串？ 和 日期？ 变量)被设置好并出现在新创建的 MediaObjectRealm DB-Entries 中。但是 ImageInfoRealm 类型的 imageInfo 不会...直接设置它，如下所示: item.setValue(oldObject.value(forKey: "imageInfo"), forKey: "imageInfo") (或 item["imageInfo"] = oldObject.value(forKey: "imageInfo")) 导致 Realm 崩溃并告诉我该对象来自另一个 Realm ，并且我得把它复制过来。

'Object is already managed by another Realm. Use create instead to copy it into this Realm.'

像上面的代码一样创建它会导致根本没有任何 MediaObjectRealm 类型的项目，即丢失所有数据(因为 NormalObjectRealm 也不再存在) 。我错过了什么吗？我基本上想要的是从 NormalObjectRealm 获取链接/引用并将其复制到新的 MediaObjectRealm。

Answer 1

经过长时间的测试并尝试不同的可能性，我成功地迁移了数据。这是我为实现这一目标所做的事情。

我用它作为基础:

class RealmMigrationObject {
    let migration: () -> ()

    init(migration: @escaping () -> ()) {
        self.migration = migration
    }
}

以及从中派生的类。像这样的东西:

class MigrationObjectToThree: RealmMigrationObject {

    init() {
        super.init(migration: MigrationObjectToThree.migration)
    }

    private static func migration() {
        print("Migration to three | migration")

        var imageInfos:   [ImageInfo]      = []

        let config = Realm.Configuration(schemaVersion: 3, migrationBlock: { migration, oldSchemaVersion in

            print("Migration to three | migrationBlock")
            print("RealmMigration: Applying migration from \(oldSchemaVersion) to 3")

            migration.deleteData(forType: "ExploreSectionObjectRealm")

            migration.enumerateObjects(ofType: "ImageInfoRealm") { oldInfo, newObject in
                guard let oldInfo = oldInfo else {
                    return
                }

                guard let id = oldInfo["id"] as? String,
                      let url = oldInfo["url"] as? String,
                      let url500 = oldInfo["url500"] as? String,
                      let url400 = oldInfo["url400"] as? String,
                      let url300 = oldInfo["url300"] as? String,
                      let url200 = oldInfo["url200"] as? String,
                      let url100 = oldInfo["url100"] as? String,
                      let colorString = oldInfo["color"] as? String,
                      let color = UIColor(hexString: colorString) else {
                    return
                }
                imageInfos.append(ImageInfo(id: id,
                                            url: url,
                                            url500: url500,
                                            url400: url400,
                                            url300: url300,
                                            url200: url200,
                                            url100: url100,
                                            color: color))
            }

        })


        Realm.Configuration.defaultConfiguration = config
        do {
            let realm = try Realm(configuration: config)
        print("Realm is located at: \(realm.configuration.fileURL?.description ?? "")")
            print(realm.configuration.fileURL?.description ?? "") // Printing here on purpose  as it's easier to copy
        } catch {
        print("Realm Error: \(error), trying to rebuild realm from scratch")

            let deleteMigrationConfig = Realm.Configuration(schemaVersion: RealmHelper.schemaVersion,
                                                            deleteRealmIfMigrationNeeded: true)
            do {
                _ = try Realm(configuration: deleteMigrationConfig)
            } catch {
                print("Failed to instantiate: \(error.localizedDescription)")
            }
        }

        RealmHelper.removeRealmFiles()
        Realm.Configuration.defaultConfiguration = Realm.Configuration(schemaVersion: 3)

        imageInfos.forEach({ $0.save() })
    }
}

从此，我刚刚为当前架构版本和目标架构版本之间的差异创建了所有迁移，并在所有迁移上循环，只需执行该给定对象的 migration 函数。