objective-c - 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对象...

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

以上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 进行排序。我目前可以使用以下代码按位置排序。

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

我不确定如何访问和使用 PositionSort。有任何想法吗？谢谢!

更新:添加了完整的功能...

- (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，我在运行时遇到了以下错误。

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

我不确定你想要精确排序，但是下面的 NSSortDescriptor 可用于使用 PositionSort 对 Person 对象进行排序值(value)。

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

也许，你正在寻找这个......