添加到关系后在coredata中找不到对象

brunobasas 发表于 Dev

布鲁诺巴萨斯

添加关系后，获取对象时出现问题。我第一次获取该类别时，总是会找到，然后当我添加到关系中时，找不到以下类别。

关系是一个Many-To-Many。

例子：

提取类别 categoryId = 10
找到类别对象
添加到父对象关系
下一个对象

如果几个类别具有相同的id，则categoryId = 10找不到

NSManagedObjectContext *private = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

   [private setParentContext:self.model.context];
    __block NSError *error = nil;

    [private performBlockAndWait:^{

        GPDeal *deal = [EKManagedObjectMapper objectFromExternalRepresentation:dic withMapping:[GPDeal objectMapping] inManagedObjectContext:private];
        for (NSDictionary *dic in responseObject[@"response"]) {

            GPCategory *category;

           //The first time always found
            if ((category = [GPCategory MR_findFirstByAttribute:@"catId" withValue:dic[@"mainAttribute"] inContext:private])) {
                NSLog(@"Found");
                [category addDealsObject:deal];

            } else {
                NSLog(@"Not Found");

            }

        }
    }];

    NSError *PrivateError = nil;
    if (![private save:&PrivateError]) {
        NSLog(@"Unresolved error %@, %@", PrivateError, [PrivateError userInfo]);
        abort();
    }

    if (!error) {
        //Save on main moc
        [self.model saveWithErrorBlock:^(BOOL success, NSError *error) {
            if (!success) {
                NSLog(@"Error saving context: %@\n%@", [error localizedDescription], [error userInfo]);
            }
        }];

    } else {
        NSLog(@"Error saving context: %@\n%@", [error localizedDescription], [error userInfo]);
    }

编辑：

解决了，我想我的问题是我忘了在每次迭代结束时保存主要上下文。

        NSManagedObjectContext *backgroundMOC = [self.model backgroundMOC:self.model.context];

        [backgroundMOC performBlockAndWait:^{

            for (NSDictionary *dic in responseObject[@"response"]) {

                GPDeal *deal = [EKManagedObjectMapper objectFromExternalRepresentation:dic withMapping:[GPDeal objectMapping] inManagedObjectContext:backgroundMOC];

                GPCategory *category;
                if ((category = [GPCategory MR_findFirstByAttribute:@"catId" withValue:dic[@"mainAttribute"] inContext:backgroundMOC])) {
                    NSLog(@"Found with mainAttribute %@", dic[@"mainAttribute"]);
                    [deal addDealCategoryObject:category];
                }

                if([backgroundMOC hasChanges]) {
                    NSError * error;
                    [backgroundMOC save:&error];

                    [self.model.context performBlockAndWait:^{
                        if([self.model.context hasChanges]) {
                            NSError * error;
                            [self.model.context save:&error];
                        }
                    }];
                }
            }
        }];

迅捷建筑师

您可能没有保存MOC链。为了清楚起见，我将关键字private替换为变量name backgroundMOC。

在上述问题上，我只能假设该行在NSManagedObjectContext *private = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; 技术上类似于：

- (NSManagedObjectContext *)backgroundMOC:(NSManagedObjectContext *)mainMOC
{
    NSManagedObjectContext * threadManagedObjectContext = [[NSManagedObjectContext alloc]
                             initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    [threadManagedObjectContext setParentContext:mainMOC];
    [threadManagedObjectContext setMergePolicy:NSMergeByPropertyObjectTrumpMergePolicy];
    return threadManagedObjectContext;
}

self.model.context作为mainMOC传递，带有self.model.context和setMergePolicy。
同样，我必须假定这self.model saveWithErrorBlock在技术上与：

[mainMOC performBlockAndWait:^{
    if([mainMOC hasChanges]) {
        NSError * error;
        [mainMOC save:&error];
        // handle error
    }
}];

如果是这样，应该对backgroundMOC（您的private参考资料）说同样的话：

[backgroundMOC performBlockAndWait:^{
    if([backgroundMOC hasChanges]) {
        NSError * error;
        [backgroundMOC save:&error];
        // handle error
    }
}];

换句话说，你要确保你backgroundMOC和mainMOC保存操作时从各自的线程上执行，与performBlockAndWait。

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