你如何压缩iOS上的Realm DB？

Question

我想定期在iOS上压缩一个Realm实例来恢复空间.我认为该过程是将数据库复制到临时位置,然后将其复制回来并使用新的default.realm文件.

我的问题是Realm()像单例和回收对象,所以我不能真正关闭它并告诉它打开新的default.realm文件.

这里的文档(https://realm.io/docs/objc/latest/api/Classes/RLMRealm.html)建议我将所有的Realm()调用包装起来,autorelease { }但它不能这么复杂.

Answer 1

完全拆除所有检索到的模型访问器确实很棘手,但遗憾的是没有其他方法可以关闭一个领域.

正如您"定期"编写的那样,每个应用程序的启动可能已经足够,具体取决于您的用例.

在启动应用程序时,在专用的自动释放池中打开Realm仍然相对容易,将压缩的副本写入不同的路径并用它替换default.realm文件.

斯威夫特2.1

func compactRealm() {
    let defaultURL = Realm.Configuration.defaultConfiguration.fileURL!
    let defaultParentURL = defaultURL.URLByDeletingLastPathComponent!
    let compactedURL = defaultParentURL.URLByAppendingPathComponent("default-compact.realm")

    autoreleasepool {
        let realm = try! Realm()
        realm.writeCopyToPath(compactedURL)
    }
    try! NSFileManager.defaultManager().removeItemAtURL(defaultURL)
    try! NSFileManager.defaultManager().moveItemAtURL(compactedURL, toURL: defaultURL)
}

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

    // further setup …

    return true
}

Swift 3.0

func compactRealm() {
    let defaultURL = Realm.Configuration.defaultConfiguration.fileURL!
    let defaultParentURL = defaultURL.deletingLastPathComponent()
    let compactedURL = defaultParentURL.appendingPathComponent("default-compact.realm")

    autoreleasepool {
        let realm = try! Realm()
        try! realm.writeCopy(toFile: compactedURL)
    }
    try! FileManager.default.removeItem(at: defaultURL)
    try! FileManager.default.moveItem(at: compactedURL, to: defaultURL)
}

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

    // further setup …

    return true
}

Answer 2

@marius给出的答案有一个问题：打开的领域可能仍引用已删除的文件。这意味着某些写操作可能最终会存储在旧的（已删除）文件中，从而导致应用丢失数据。

compactRealm方法的正确实现如下所示（第3步）：

func compactRealm() {
    let defaultURL = Realm.Configuration.defaultConfiguration.fileURL!
    let defaultParentURL = defaultURL.deletingLastPathComponent()
    let compactedURL = defaultParentURL.appendingPathComponent("default-compact.realm")

    autoreleasepool {
        let realm = try! Realm()
        try! realm.writeCopy(toFile: compactedURL)
    }
    try! FileManager.default.removeItem(at: defaultURL)
    try! FileManager.default.moveItem(at: compactedURL, to: defaultURL)
}

这个问题一直让我发疯，直到在这里找到答案