核心数据对多关系问题

Question

我将核心数据模型更改为多对多关系。我相信这是正确的模型。我需要能够做到以下几点：

（1）一顿饭可以含有很多食物 （2）Food iteme可以链接到许多餐食

当我尝试获取所有食物以获得某种膳食时，我收到以下错误。当它是一对多的时候就可以工作，但是因为我把它变成了一个多对多的关系。

*** 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

我认为只是谓词需要改变：

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

因为meals现在是一个集合。