托管对象上下文不合并来自后台上下文的更改
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【中文标题】托管对象上下文不合并来自后台上下文的更改【英文标题】:Managed object context not merging changes from background context 【发布时间】:2013-05-10 12:56:31 【问题描述】:我有一个双重托管对象上下文设置,其中我有一个父/子 MOC 关系。父级负责直接写入私有队列(NSPrivateQueueConcurrencyType)上的数据库,然后我有一个子上下文负责为主线程(NSMainQueueConcurrencyType)拉取和保存数据。
当我对主队列上下文进行更改并保存它时,上下文会正常工作,然后将更改合并到后台队列上下文并在后台线程上写入数据库。
我遇到的问题是当我将数据直接写入后台队列上下文,然后尝试将其合并到主队列上下文时。对象正确存储在商店中,当我合并更改时,它似乎可以工作。但是,如果我尝试在将数据保存到存储后直接针对主队列上下文发出 NSFetchRequest,那么数据是陈旧的,而不是正确的更新数据。
以下是代码摘录,可以帮助大家了解我在做什么。需要注意的是从 JSON 返回 NSManagedObjects 的逻辑可以正常工作。此外,我已经测试并且在 UI 尝试对主队列 MOC 发出任何获取请求之前运行 mergeChangesFromContextDidSaveNotification。大家有什么想法吗?
// Context Setup
- (NSManagedObjectContext *)backgroundWriterManagedObjectContext
if (_backgroundWriterManagedObjectContext != nil)
return _backgroundWriterManagedObjectContext;
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
_backgroundWriterManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
_backgroundWriterManagedObjectContext.persistentStoreCoordinator = coordinator;
_backgroundWriterManagedObjectContext.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy;
_backgroundWriterManagedObjectContext.undoManager = nil;
return _backgroundWriterManagedObjectContext;
- (NSManagedObjectContext *)managedObjectContext
if (_managedObjectContext != nil)
return _managedObjectContext;
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
_managedObjectContext.parentContext = _backgroundWriterManagedObjectContext;
_managedObjectContext.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy;
_managedObjectContext.stalenessInterval = 0.0;
return _managedObjectContext;
// save MOC
- (void)saveManagedObjectContext
@try
// perform synchronous process to save to the main MOC
[_managedObjectContext performBlockAndWait:^(void)
__block NSError *error = nil;
// push any changes in the main context to the background writer context
if (![_managedObjectContext tryLock])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Unable To Lock Managed Object Context: %@", error.localizedDescription]];
if (![_managedObjectContext save:&error])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Error Saving Managed Object Context: %@", error.localizedDescription]];
[_managedObjectContext unlock];
// save the background writer context
[_backgroundWriterManagedObjectContext performBlock:^(void)
error = nil;
if (![_backgroundWriterManagedObjectContext tryLock])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Unable To Lock Background Writer Managed Object Context: %@", error.localizedDescription]];
if (![_backgroundWriterManagedObjectContext save:&error])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Error Saving Background Writer Managed Object Context: %@", error.localizedDescription]];
[_backgroundWriterManagedObjectContext unlock];
];
];
@catch (NSException *exception)
[VS_Log VS_LogException:exception];
// This code runs when attempting to save objects from a web service call
[_backgroundWriterManagedObjectContext performBlock:^(void)
// create a new process object and add it to the dictionary
__block VS_CoreDataRequest *request = [[VS_CoreDataRequest alloc] init];
// .. LOGIC HERE DESERIALIZES THE JSON AND RETURNS AN ARRAY OF NSMANAGEDOBJECTS
// perform synchronous process to save to the main MOC
@try
NSError *error = nil;
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeChangesFromContextDidSaveNotification:) name:NSManagedObjectContextDidSaveNotification object:_backgroundWriterManagedObjectContext];
if (![_backgroundWriterManagedObjectContext tryLock])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Unable To Lock Background Writer Managed Object Context: %@", error.localizedDescription]];
if (![_backgroundWriterManagedObjectContext save:&error])
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManger - Error Saving Background Writer Managed Object Context: %@", error.localizedDescription]];
[_backgroundWriterManagedObjectContext unlock];
// submit changes back to the forground context
[_managedObjectContext performBlock:^(void)
NSMutableArray *objects = [[NSMutableArray alloc] init];
// iterate through the updated objects and find them in the main thread MOC
for (VS_BaseManagedObject *object in request.objects)
// get the object from the main managed object context
NSError *error;
NSManagedObject *obj = [_managedObjectContext existingObjectWithID:object.objectID error:&error];
if (error)
[VS_Log VS_LogError:[NSString stringWithFormat:@"VS_CoreDataManager - Error: %@", error.localizedDescription]];
if (obj)
[_managedObjectContext refreshObject:obj mergeChanges:YES];
[objects addObject:obj];
// RETURN FROM METHOD SO UI CAN REGAIN CONTROL
];
@catch (NSException *exception)
[VS_Log VS_LogException:exception];
return;
];
// Merges changes from parent to child context
- (void)mergeChangesFromContextDidSaveNotification:(NSNotification *)notification
// remove observer
[[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:_backgroundWriterManagedObjectContext];
// merge the changes
[_managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
【问题讨论】:
在您提供的信息中有些东西没有意义,因为您的代码和概念看起来不错。您是否使用 FRC 将数据提供给视图?如果是这样,我怀疑它与您的 FRC 有更多关系。我不确定独立提取是否会根据您的需要更新 MOC。我会调查的。 【参考方案1】:您没有调用进程挂起的更改。
【讨论】:
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