10

背景

我有以下对象树：

Name                       Project       
Users                      nil           
  John                     nil            
    Documents              nil           
      Acme Project         Acme Project    <--- User selects a project
        Proposal.doc       Acme Project  
          12:32-12:33      Acme Project  
          13:11-13:33      Acme Project  
            ...thousands more entries here...

  • 用户可以将组分配给项目。所有后代都设置为该项目。

  • 这会锁定主线程，所以我正在使用 NSOperations。

  • 我正在使用 Apple 批准的方式来执行此操作，观察NSManagedObjectContextDidSaveNotification并合并到主要上下文中。

问题

我的保存失败并出现以下错误：

Failed to process pending changes before save. The context is still dirty after 100 attempts. Typically this recursive dirtying is caused by a bad validation method, -willSave, or notification handler.

我试过的

我已经剥离了我的应用程序的所有复杂性，并制作了我能想到的最简单的项目。并且错误仍然发生。我试过了：

  • 将队列上的最大操作数设置为 1 或 10。

  • refreshObject:mergeChanges:在 NSOperation 子类中的几个点调用。

  • 在托管对象上下文上设置合并策略。

  • 构建和分析。它是空的。

我的问题

如何在 NSOperation 中设置关系而不让我的应用崩溃？当然这不能是Core Data的限制吗？它可以？

编码

下载我的项目：http ://synapticmishap.co.uk/CDMTTest1.zip

主控制器

@implementation JGMainController

-(IBAction)startTest:(id)sender {
    NSManagedObjectContext *imoc = [[NSApp delegate] managedObjectContext];

    JGProject *newProject = [JGProject insertInManagedObjectContext:imoc];
    [newProject setProjectName:@"Project"];
    [imoc save];

        // Make an Operation Queue
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue setMaxConcurrentOperationCount:1]; // Also crashes with a higher number here (unsurprisingly)

    NSSet *allTrainingGroupsSet = [imoc fetchAllObjectsForEntityName:@"TrainingGroup"];

    for(JGTrainingGroup *thisTrainingGroup in allTrainingGroupsSet) {
        JGMakeRelationship *makeRelationshipOperation = [[JGMakeRelationship alloc] trainGroup:[thisTrainingGroup objectID] withProject:[newProject objectID]];
        [queue addOperation:makeRelationshipOperation];
        makeRelationshipOperation = nil;
    }
}

    // Called on app launch.
-(void)setupLotsOfTestData {
         // Sets up 10000 groups and one project
}

@end

进行关系操作

@implementation JGMakeRelationshipOperation

-(id)trainGroup:(NSManagedObjectID *)groupObjectID_ withProject:(NSManagedObjectID *)projectObjectID_ {
    appDelegate = [NSApp delegate];
    imoc = [[NSManagedObjectContext alloc] init];
    [imoc setPersistentStoreCoordinator:[appDelegate persistentStoreCoordinator]];
    [imoc setUndoManager:nil];
    [imoc setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(mergeChanges:) 
                                                 name:NSManagedObjectContextDidSaveNotification 
                                               object:imoc];
    groupObjectID = groupObjectID_;
    projectObjectID = projectObjectID_;
    return self;
}

-(void)main {
    JGProject       *project        = (JGProject *)[imoc objectWithID:projectObjectID];
    JGTrainingGroup *trainingGroup = (JGTrainingGroup *)[imoc objectWithID:groupObjectID];
    [project addGroupsAssignedObject:trainingGroup];
    [imoc save];

    trainingGroupObjectIDs = nil;
    projectObjectID = nil;
    project = nil;
    trainingGroup = nil;
}

-(void)mergeChanges:(NSNotification *)notification {
    NSManagedObjectContext *mainContext = [appDelegate managedObjectContext];
    [mainContext performSelectorOnMainThread:@selector(mergeChangesFromContextDidSaveNotification:)
                                  withObject:notification
                               waitUntilDone:YES];  
}

-(void)finalize {
    appDelegate = nil;
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    imoc = nil;
    [super finalize];
}
@end


@implementation NSManagedObjectContext (JGUtilities)

-(BOOL)save {
         // If there's an save error, I throw an exception
}

@end

数据模型

数据模型

更新 1

我已经进行了更多实验，即使没有合并，仍然会抛出异常。只需在修改关系后将托管对象上下文保存在另一个线程中就足够了。

我有一个与应用程序委托共享的持久存储协调器。我尝试为与我的数据存储具有相同 URL 的线程创建一个单独的 NSPersistentStoreCoordinator，但 Core Data 抱怨。

I'd love to suggestions on how I can make a coordinator for the thread. The core data docs allude to there being a way of doing it, but I can't see how.

4

1 回答 1

10

You are crossing the streams (threads in this case) which is very bad in CoreData. Look at it this way:

  1. startTest called from a button (is IBAction, assuming button tap) on Main thread
  2. Your for loop creates a JGMakeRelationship object using the initializer trainGroup: withProject: (this should be called init, and probably call super, but that's not causing this issue).
  3. You create a new managed object context in the operation, on the Main thread.
  4. Now the operation queue calls the operations "main" method from a worker thread (put a breakpoint here and you'll see it's not on the main thread).
  5. 您的应用程序蓬勃发展，因为您从与创建它的线程不同的线程访问了托管对象上下文。

解决方案：

在操作的 main 方法中初始化托管对象上下文。

于 2010-10-20T08:17:04.720 回答