更新记录时似乎我NSPredicate的不起作用。Core Data在执行 fetch 请求时，同样NSPredicate可以正常工作。
当我执行 aBatch 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？
这是我进行更新的代码：
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
}
这是我的 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()
}
}
});
}