ios - 向核心数据添加属性值 IF 值已存在

Question

我不得不说，论坛上的每个人都对我学习核心数据的尝试非常有帮助。

我正在向我的核心数据实体添加属性值，并在用户选择一行时创建关系，如下所示：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath*)indexPath
{

UIAlertView *messageAlert = [[UIAlertView alloc]
                                 initWithTitle:@"Row Selected" message:@"Added to Routine!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

    NSManagedObjectContext *context = [self managedObjectContext];

    // Create a new device
    ExcerciseInfo *info = [_fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObject *routineEntity = [NSEntityDescription insertNewObjectForEntityForName:@"Routines"inManagedObjectContext:context];
NSManagedObject *routineEntityDetail = [NSEntityDescription insertNewObjectForEntityForName:@"RoutinesDetails" inManagedObjectContext:context];

[routineEntityDetail setValue:routineEntity forKey:@"routineinfo"];

    [routineEntity setValue: RoutineText  forKey:@"routinename"];
    [routineEntityDetail setValue: info.details.muscle  forKey:@"image"];

IF statement如果已经存在，我将如何包含一个routinename新条目将添加到现有关系中？

这很容易从当前代码中实现吗？因此，测试例程将被分组而不是单独显示，并且详细视图将包括这两个条目。NSPredicate这里合适吗？或者也许使用distinctUnionOfObjects?

您的想法和意见将不胜感激。

按照要求 -

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Routines" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc]
    initWithKey:@"routinename" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController =
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                        managedObjectContext:managedObjectContext sectionNameKeyPath:nil
                                                   cacheName: nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;

Answer 1