Question

在更新NSPredicate记录时似乎我的Core Data无效。在执行获取请求时，相同的NSPredicate可以正常工作。

当我执行Batch Update时，它只会创建新的重复记录，而不是按预期覆盖现有记录。为什么哦为什么？

以下是执行更新的代码：

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

}

以下是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NSBatchUpdateRequest的文档（对你很遗憾，Apple！）。但是WWDC 2014，会议225（这里是ASCII transcript）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，如果您对集中更新数据库感兴趣，例如在特定列上设置标记，然后在UI中反映这些更改，则您需要获取结果或托管对象ID返回，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。

您必须为批量请求指定其他resultType：

batchRequest.resultType = .UpdatedObjectIDsResultType

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

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

尝试使用NSBatchUpdateRequest的代码而不复制swift3中的记录

func batchUpdate{ 
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let managedContext = appDelegate.managedObjectContext
        let batchRequest = NSBatchUpdateRequest(entityName: "ENTITY_NAME")
        batchRequest.propertiesToUpdate = [ "PROPERTY_NAME" : "CHANGE_VALUE`enter code here`"]
        batchRequest.resultType = .updatedObjectIDsResultType

        do{
           let objectIDs = try managedContext.execute(batchRequest) as! NSBatchUpdateResult
           let objects = objectIDs.result as! [NSManagedObjectID]

            objects.forEach({ objID in
                let managedObject = managedContext.object(with: objID)
                managedContext.refresh(managedObject, mergeChanges: false)
            })
        } catch {
        }
}

Answer 3

您的doesMessageExist功能错误。

您检查获取请求的计数不等于NSNotFound，它只会在发生错误时执行。如果找不到该消息，它将返回零，如果可以找到，它将返回一个（或多个，如果你有多个具有相同ID的对象）。

目前，您的代码会说该消息始终存在。

顺便提一下，这个问题中的代码都没有创建新对象，并且executeRequest不是NSManagedObjectContext上的方法，所以你应该在问题中包含你的实现。

Swift核心数据批量更新创建重复记录而不是覆盖

3 个答案: