使用 NSFetchedResultsController 对多对多关系进行排序

发布于 2024-09-26 14:45:21 字数 2260 浏览 3 评论 0原文

我尝试在我的应用中使用 NSFetchedResultsController，但在对数据进行排序时遇到问题。当尝试使用比实体低两级的关系对结果进行排序时，出现以下错误：

* 由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'，原因： “此处不允许使用多对多密钥”

我的数据模型是这样设置的：

项目<<--->类别<--->>排序顺序 <<--->商店

换句话说：每件商品都属于一个类别。对于包含特定类别的每个商店，类别可以具有不同的排序顺序。

因此，我正在创建一个获取请求来查找某个商店的所有商品，并希望使用类别名称作为部分来显示结果，并按排序顺序进行排序。

当我执行提取（下面最后一行）时，我收到上述错误。

 NSManagedObjectContext* context = [appDelegate managedObjectContext];
 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(status != %d) AND (ANY category.sort.include == YES) AND (ANY category.sort.store == %@)", ItemStatusDefault, store];

 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:context];
 [fetchRequest setEntity:entity];
 [fetchRequest setPredicate:predicate];

 NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"category.sort.order" ascending:YES];
 NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
 [fetchRequest setSortDescriptors:sortDescriptors];
 [sortDescriptors release];
 [sortDescriptor release];

 self.resultsController = [[NSFetchedResultsController alloc]
             initWithFetchRequest:fetchRequest
             managedObjectContext:context
             sectionNameKeyPath:@"category.name"
             cacheName:nil];
 [fetchRequest release];

 NSError *error;
 BOOL success = [self.resultsController performFetch:&error];

如果我将排序更改为类别名称，那么它就会起作用。

 NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"category.name" ascending:YES];

如何让 NSSortDescriptor 按排序顺序进行排序？

更新：所以看来这是不可能的。我收到了创建瞬态属性并对其进行排序的建议，但是苹果文档明确指出

您无法使用谓词获取基于瞬态属性

我的结论是我不能立即使用 NSFetchedResultsController 。我需要访问 NSFetchResultsController 提供的对象数组并在内存中排序，或者设置我自己的获取请求并跳过 NSFetchedResultsController。

原文

I'm trying to use the NSFetchedResultsController in my app, but have a problem to sort my data. I get the following error when trying to sort the result using a relationship that is two levels down from the entity:

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

My data model is set up this way:

Item <<---> Category <--->> SortOrder
<<---> Store

In other words: Each item belongs to one category. Categories can have different sort orders for each store that includes a certain category.

So, I'm creating a fetch request to find all items for a certain store and would like to present the result using category names as sections, and sorted on the sort order.

When I perform the the fetch (last line below), I get the above error.

 NSManagedObjectContext* context = [appDelegate managedObjectContext];
 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(status != %d) AND (ANY category.sort.include == YES) AND (ANY category.sort.store == %@)", ItemStatusDefault, store];

 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:context];
 [fetchRequest setEntity:entity];
 [fetchRequest setPredicate:predicate];

 NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"category.sort.order" ascending:YES];
 NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
 [fetchRequest setSortDescriptors:sortDescriptors];
 [sortDescriptors release];
 [sortDescriptor release];

 self.resultsController = [[NSFetchedResultsController alloc]
             initWithFetchRequest:fetchRequest
             managedObjectContext:context
             sectionNameKeyPath:@"category.name"
             cacheName:nil];
 [fetchRequest release];

 NSError *error;
 BOOL success = [self.resultsController performFetch:&error];

If I change the sorting to, say, category names, it works.

 NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"category.name" ascending:YES];

How can I get the NSSortDescriptor to sort on the sort order?

UPDATE:
So it seems this is not possible. I got a suggestion to create a transient property and sort on that, but Apple documentation clearly states

You cannot fetch using a predicate
based on transient properties

My conclusion here is that I cannot use NSFetchedResultsController out of the box. I need to either access the array of objects the NSFetchResultsController gives me and sort in memory, or setup my own fetch requests and skip NSFetchedResultsController.

分享到QQ

分享到微博