iOS:如何使用NSSortDescriptor对关系中的值进行排序？

Question

我的数据模型中有两个关系对象...

1. 人{姓名,职位,职称}
2. 位置{position,PositionSort}

上面的每一个都有自己的类文件(NSManagedObject的子类).我正在尝试按上面的PositionSort排序.我目前可以使用以下代码按位置排序.

NSSortDescriptor *sortDescriptorPosition = [[NSSortDescriptor alloc] initWithKey:@"position" ascending:YES];

我不确定我是如何访问和使用PositionSort的.有任何想法吗？谢谢!

更新:添加全功能...

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sortDescriptorState = [[NSSortDescriptor alloc] initWithKey:@"position.positionSort" ascending:YES];

    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptorState, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];


    NSPredicate *searchPredicate = [NSPredicate predicateWithFormat:@"(companyID == %@)", company.companyID];
    [fetchRequest setPredicate:searchPredicate];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"position.positionDescription" cacheName:nil];

    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
}

使用上面的代码我收到以下错误Runtime.

2012-08-12 10:29:45.499 College[269:707] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSCFString 0xd6bd310> valueForUndefinedKey:]: this class is not key value coding-compliant for the key positionDescription.'

Answer 1

我不确定您是否要完全排序,但以下内容NSSortDescriptor可用于Person使用PositionSort值对对象进行排序.

NSSortDescriptor *sortDescriptorPosition = [[NSSortDescriptor alloc] initWithKey:@"position.PositionSort" ascending:YES];

也许,你找了这个......