核心数据并发 - 收集在枚举期间发生了变化 [英] Core Data Concurrency - Collection was mutated while being enumerated

问题描述

我在Core Data应用程序中添加了一些名为 Transaction 的对象。这些交易与一个帐户相关联。

I'm adding some objects called Transactions in my Core Data application. Those transactions are linked to an account.

我想在所有交易保存后更新帐户金额。有时会出现并发异常

I'd like to update the account amount when all the transactions are saved. Sometimes there is a concurrency exception

枚举时发生了变异

"Collection was mutated while being enumerated"

在 NSArray * matches = [managedObjectContext executeFetchRequest：request error：& error]; 中的行accountmanagedObjectWithId 方法。

at NSArray *matches = [managedObjectContext executeFetchRequest:request error:&error]; line in accountManagedObjectWithId method.

//TransactionsManager

- (BOOL)addRepeatTransaction:(Transaction *)transaction{

    Account *accountTrx = transaction.account;
    double accountAmount = accountTrx.amount;
    for (int i =0; i<nbRepeat; i++){
         accountAmount +=transactionBiz.amount;
        [[Persister instance] registerTransaction:transaction];
    }
    [[Persister instance]editAmountAccount:transaction.account amount:accountAmount];
    [[Persister instance]saveContext];

    return YES;
}

//Persister

-(id)init {
    if (self = [super init]){
        managedObjectContext = [appDelegate managedObjectContext];
        return self;
    }
    return nil;
}

-(BOOL)registerTransaction:(Transaction *)transaction {
    TransactionManagedObject *transactionsRow = (TransactionsManagedObject *)[NSEntityDescription insertNewObjectForEntityForName:@"Transactions" inManagedObjectContext:managedObjectContext];

    transactionsRow.idTransaction =  [NSNumber numberWithInt:transaction.idTransaction];
    transactionsRow.name = transaction.name;
    transactionsRow.amount = [NSNumber numberWithDouble:transaction.amount];
    [...]
    transactionsRow.account = [[Finder instance] accountManagedObjectWithId:transaction.account.idAccount];

    return YES;
}

-(BOOL)editAmountAccount:(Account *)asset amount:(double)amount {
    AccountManagedObject *accountRow = [[Finder instance] accountManagedObjectWithId:account.idAccount];

    accountRow.amount = [NSNumber numberWithDouble:amount];
    return YES;
}

-(AccountManagedObject *)accountManagedObjectWithId:(NSInteger)idAccount {

    NSFetchRequest *request = [[NSFetchRequest alloc]init];
    [request setEntity:[NSEntityDescription entityForName:@"Accounts" inManagedObjectContext:managedObjectContext]];

    //Predicate
    NSString *recordedIdAccount = @"idAccount";
    NSNumber *numberIdAccount = [NSNumber numberWithInt:idAccount];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %@", recordedIdAccount,numberIdAccount];
    [request setPredicate:predicate];

    //Execute
    NSError *error;
    NSArray *matches = [managedObjectContext executeFetchRequest:request error:&error];
    NSInteger nbResult = [matches count];
    if(nbResult==1){
        return [matches objectAtIndex:0];
    }
    if(nbResult==0){
        [...]
        return nil;
    }
    if(nbResult>0){
        [...]
        return nil;
    }
    return nil;
}

//UI call
[...]
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
     //Save
     [[TransactionsManager instance] addRepeatTransaction:transactionToAdd];

     dispatch_async(dispatch_get_main_queue(), ^{

          //Call the delegate
          [self.delegate theSaveButtonOnTheAddTransactionTVCWasTapped:self];
      });
});

---

@Valentin Radu

---

@Valentin Radu

我试过了，但问题仍然存在。我必须为每次添加设置一个 managedObjectContext 。这是工作，但它减慢了应用程序。这是正确的方法吗？

I've tried that but the problem remains. I have to set up a managedObjectContext for each adding. This is working but it slows the application. Is it the right way to do it?

-(BOOL)registerTransaction:(Transaction *)transaction{
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
   [moc setPersistentStoreCoordinator:[[self managedObjectContext] persistentStoreCoordinator]];


    TransactionsManagedObject *transactionsRow = (TransactionsManagedObject *)[NSEntityDescription insertNewObjectForEntityForName:@"Transactions" inManagedObjectContext:moc];

    transactionsRow.idTransaction =  [NSNumber numberWithInt:transaction.idTransaction];
    transactionsRow.name = transaction.name;
    transactionsRow.amount = [NSNumber numberWithDouble:transaction.amount];
    [...]
    transactionsRow.account = [[Finder instance] accountManagedObjectWithId:transaction.account.idAccount andManagedContext:moc]];

    NSError *error = nil;
    if (![moc save:&error]) {
        [[ErrorManager instance] addError:error];
        return NO;
    }

    return YES;
}

推荐答案

一个上下文，如果您对核心数据对象执行并行操作，那么这是错误的。你应该每个线程有一个上下文，并在每次保存时合并上下文。 Apple的核心数据指南更详细地讨论了这一点。

You seem to be using only one context, which is wrong if you have parallel operations executing on your core data objects. You should have a context per thread and merge the contexts every time you save. Apple's Core Data Guideline talks about this in more detail.

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