Question

我有一个实际上版本号为2.4的应用程序。从1.0版本开始，我在每个更新中都使用app delegate中的核心数据。所以每次更新我都会在1.0版附带的原始数据库中添加元素。这是添加元素的方式，例如：

 //ADD ELEMENT
if (context == nil) { context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; }
Negozi *newElement = [NSEntityDescription insertNewObjectForEntityForName:@"Elements" inManagedObjectContext:context];
newElement.name=@"element name";
newElement.id=@"101";
[context save:nil];

1.0附带的db包括1到100的newElement.id，来自newElement.id 101是在应用程序的一个较新版本中添加的元素。问题来自deletObject。通过这种方式，我可以从我的上下文中删除一个对象：

if (context == nil) { context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; }
NSError *error=nil;

///DELETE Element with id 101
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Elements" inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];

NSString *ElementToDelete=[NSString stringWithFormat:@"%@",@"101"];

for (int i=0; i<[fetchedObjects count]; i++) {

    if ([[[fetchedObjects objectAtIndex:i] valueForKey:@"id"] isEqualToString:ElementToDelete]) {

        [contesto deleteObject:[fetchedObjects objectAtIndex:i]];

    }
}

 [contesto save:nil];

使用此代码，我可以成功删除id 101中的对象（添加了应用程序更新的对象）。如果我尝试删除id <100的一些元素，我会收到此错误：

CoreData: error: failed to resolve optimistic locking failure: optimistic locking failure with (null)

这是我的托管对象上下文代码：

#pragma mark -
#pragma mark Core Data stack


- (NSManagedObjectContext *)managedObjectContext {

if (managedObjectContext_ != nil) {
    return managedObjectContext_;
}

NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
    managedObjectContext_ = [[NSManagedObjectContext alloc] init];
    [managedObjectContext_ setPersistentStoreCoordinator:coordinator];

}
return managedObjectContext_;
}



- (NSManagedObjectModel *)managedObjectModel {

if (managedObjectModel_ != nil) {
    return managedObjectModel_;
}

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Elements" withExtension:@"momd"];
managedObjectModel_ = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];    
return managedObjectModel_;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

if (persistentStoreCoordinator_ != nil) {
    return persistentStoreCoordinator_;
}

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Elements.sqlite"];

NSString *storePath = [[[self applicationDocumentsDirectory] path] stringByAppendingPathComponent:@"Elements.sqlite"];

NSFileManager *fileManager = [NSFileManager defaultManager];
// If the expected store doesn't exist, copy the default store.
if (![fileManager fileExistsAtPath:storePath]) {
    NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@"Elements" ofType:@"sqlite"];
    if (defaultStorePath) {
        [fileManager copyItemAtPath:defaultStorePath toPath:storePath error:NULL];
        [self addSkipBackupAttributeToItemAtURL:[NSURL fileURLWithPath:defaultStorePath]];
    }
}



NSError *error = nil;
persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];


NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:

                         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,

                         [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];



if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]) {

    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}    

return persistentStoreCoordinator_;



}

为什么我不能删除最初存储在db？

中的对象

Answer 1

您正在遍历获取结果列表，然后想要修改它（通过删除元素）。这可能会导致您所描述的问题。

相反，清理代码并只获取要删除的元素，而不是所有元素。这消除了循环，也更有效。

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:"Element"];
request.predicate = [NSPredicate predicateWithFormat:@"id = %@", @(101)];
NSArray *result = [context executeFetchRequest:request error:&fetchError];
if (result.count == 1) {
    NSManagedObject *element = result.firstObject;
    [context deleteObject:element];
    [context save:&saveError];
}
else { NSLog(@"Element not found."); }

CoreData：错误：无法解决乐观锁定失败：乐观锁定失败（null），只有旧记录，为什么？

1 个答案: