Swift核心数据批量更新创建重复记录而不是覆盖

Question

NSPredicate在更新Core Data记录时似乎我的工作不正常.在执行获取请求时,同样NSPredicate可以正常工作.

当我这样做时Batch Update,它只是创建新的重复记录而不是按预期覆盖现有的记录.为什么哦为什么？

这是我的代码进行更新:

let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate

lazy var managedObjectContext : NSManagedObjectContext? = {
    if let managedObjectContext = self.appDelegate.managedObjectContext {
        return managedObjectContext
    }
    else {
        return nil
    }
    }()

func doesMessageExist(id: String) -> Bool {
    let fetchRequest = NSFetchRequest(entityName: "ChatMessage")
    let predicate = NSPredicate(format: "id == %@", id)
    fetchRequest.predicate = predicate
    fetchRequest.fetchLimit = 1

    let count = managedObjectContext!.countForFetchRequest(fetchRequest, error: nil)
    return (count > 0) ? true : false
}

func updateMessage(chatMessage: ChatMessage) {
    var batchRequest = NSBatchUpdateRequest(entityName: "ChatMessage")

    if doesMessageExist(chatMessage.id) {
        batchRequest.predicate = NSPredicate(format: "id == %@", chatMessage.id)
    }

    batchRequest.propertiesToUpdate = [
        "id" : chatMessage.id,
        "senderUserId" : chatMessage.senderUserId,
        "senderUsername" : chatMessage.senderUsername,
        "receiverUserId" : chatMessage.receiverUserId,
        "receiverUsername" : chatMessage.receiverUsername,
        "messageType" : chatMessage.messageType,
        "message" : chatMessage.message,
        "timestamp" : chatMessage.timestamp
    ]

    batchRequest.resultType = .UpdatedObjectsCountResultType
    var error : NSError?
    var results = self.managedObjectContext!.executeRequest(batchRequest, error: &error) as NSBatchUpdateResult
    if error == nil {
        println("Update Message: \(chatMessage.id) \(results.result)")
        appDelegate.saveContext()
    }
    else {
        println("Update Message Error: \(error?.localizedDescription)")
    }
}

这是我的ChatMessage类:

class ChatMessage: NSManagedObject {

    @NSManaged var id: String
    @NSManaged var message: String
    @NSManaged var messageType: String
    @NSManaged var receiverUserId: String
    @NSManaged var receiverUsername: String
    @NSManaged var senderUserId: String
    @NSManaged var senderUsername: String
    @NSManaged var timestamp: NSDate

}

这是AppDelegate中的核心数据堆栈:

lazy var applicationDocumentsDirectory: NSURL = {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "com.walintukai.LFDate" in the application's documents Application Support directory.
    let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
    return urls[urls.count-1] as NSURL
}()

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = NSBundle.mainBundle().URLForResource("LFDate", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
}()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator? = {
    // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
    // Create the coordinator and store
    var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("LFDate.sqlite")
    var error: NSError? = nil
    var failureReason = "There was an error creating or loading the application's saved data."
    if coordinator!.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil, error: &error) == nil {
        coordinator = nil
        // Report any error we got.
        let dict = NSMutableDictionary()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason
        dict[NSUnderlyingErrorKey] = error
        error = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog("Unresolved error \(error), \(error!.userInfo)")
        abort()
    }

    return coordinator
}()

lazy var managedObjectContext: NSManagedObjectContext? = {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
    let coordinator = self.persistentStoreCoordinator
    if coordinator == nil {
        return nil
    }
    var managedObjectContext = NSManagedObjectContext()
    managedObjectContext.persistentStoreCoordinator = coordinator
    managedObjectContext.mergePolicy = NSOverwriteMergePolicy
    return managedObjectContext
}()

// MARK: - Core Data Saving support

func saveContext () {
    dispatch_async(dispatch_get_main_queue(),{
        if let moc = self.managedObjectContext {
            var error: NSError? = nil
            if moc.hasChanges && !moc.save(&error) {
                // Replace this implementation with code to handle the error appropriately.
                // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                NSLog("Database Save Error: \(error), \(error!.userInfo)")
                abort()
            }
        }
    });
}

Answer 1

可悲的是,没有任何文件NSBatchUpdateRequest(对你很遗憾,Apple!).但是,WWDC 2014,会议225(这里是ASCII转录)涵盖了批量更新请求.

在会话中,提到批量更新绕过NSManagedObjectContext并直接在持久性存储中进行更改.所以你必须自己刷新对象:

因此,如果您有兴趣集中更新数据库,例如在特定列上设置标志,然后在UI中反映这些更改,则需要返回结果或托管对象ID,因此您可以告诉对象,告诉托管对象上下文刷新具有这些ID的对象.

您必须resultType为批处理请求指定其他:

batchRequest.resultType = .UpdatedObjectIDsResultType

然后在执行请求后,您必须使用返回的数组刷新对象NSManagedObjectID(来自Big Nerd Ranch的代码示例,在Swift中重写):

for objectsID in objectsIDs {
    var error : NSError? = nil
    if let object = context.existingObjectWithID(objectsID as NSManagedObjectID, error: &error) {
        context.refreshObject(object, mergeChanges: true)
    }
}

Answer 2

你的doesMessageExist函数是错误的。

您检查获取请求的计数不等于NSNotFound，只有在发生错误的情况下才会执行此操作。如果找不到该消息，它将返回零，如果可以找到，它将返回一（或多个，如果您有多个具有相同 ID 的对象）。

目前，您的代码将表明该消息始终存在。

顺便说一句，这个问题中的代码都没有创建新对象，也不executeRequest是 NSManagedObjectContext 上的方法，因此您可能应该在问题中包含该方法的实现。