添加到关系后未在coredata中找到对象

Question

我在添加关系后获取对象时遇到问题.我第一次获取类别,总是找到,然后当我添加到关系时,找不到以下类别.

这种关系是一种Many-To-Many.

例:

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

• 如果几个类别相同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];
                        }
                    }];
                }
            }
        }];

Answer 1

您可能缺乏保存 MOC 链的能力。private为了清楚起见，我用变量 name替换了关键字backgroundMOC。

对于上面的问题，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;
}

作为 mainMOC传递self.model.context，带有 aself.model.context和 a setMergePolicy。
同样，我必须假设这self.model saveWithErrorBlock在技术上与以下内容相同：

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

backgroundMOC如果是这样， （您的参考）也应该这样说private：

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

换句话说，您希望确保您的backgroundMOC和mainMOCsave 操作是从各自的线程执行的，并且performBlockAndWait.