Not found an object in coredata after added to a relationship

Question

I have an issue with the fetch of an object after added in a relationship. The first time that i fetch the category, always found, then when i added to the relationship the following categories not found.

The relationship is a Many-To-Many.

Example:

• Fetch category with categoryId = 10
• Found category object
• Added to the parent object relationship
• Next object

• If the several categories has the same id, categoryId = 10, not found

  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]);
      }
  

EDIT:

Solved , I guess my problem was that i forgot to save the main context in the end of each iteration .

        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

You may lack saving the MOC chain. For clarity, I have replaced the keyword private with the variable name backgroundMOC.

On the question above, I can only assume that the line NSManagedObjectContext *private = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; is technically similar to:

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

passing self.model.context as mainMOC, with a self.model.context and a setMergePolicy.
Similarly, I must assume that self.model saveWithErrorBlock is technically identical to:

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

If so, the same should be said of the backgroundMOC (your private reference):

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

---

In other words, you want to ensure that your backgroundMOC and mainMOC save operation is executed from their respective threads, with performBlockAndWait.