iphone - 核心数据对多关系问题

Question

我将核心数据模型更改为一对多关系。我相信这是正确的模型。我需要能够执行以下操作:

(1) 一顿饭可以包含很多食物(2) 一个Food iteme可以链接到多个Meals

当我尝试获取某餐的所有食物时出现以下错误。这在一对多关系时有效，但自从我将其更改为一对多关系后就不行了。

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'

- (NSFetchedResultsController *)fetchedResultsController 
{       
    self.context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 

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

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Food" inManagedObjectContext:self.context];

    [fetchRequest setEntity:entity];

    NSPredicate *foodPredicate = [NSPredicate predicateWithFormat:@"meals == %@", self.meal];
    [fetchRequest setPredicate:foodPredicate];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];

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


    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    [fetchRequest release];
    [theFetchedResultsController release];

    return _fetchedResultsController;
}

Answer 1

只是谓词需要改变，我认为:

NSPredicate *foodPredicate = [NSPredicate predicateWithFormat:@"ANY meals == %@", self.meal];

因为 meals 现在是一套。