索引501处的获取对象具有无序部分名称'JOURNAL OF APPLIED PHYSICS。对象必须按节名称排序'

Question

我有一个包含期刊栏目名称的文章数据库。一篇文章是“应用物理学杂志”，另一篇是“应用物理学报”。当我使用

[[NSSortDescriptor alloc] initWithKey:@"Journal" ascending:YES elector:@selector(caseInsensitiveCompare:)]

获取数据，它给我错误信息。

The fetched object at index 501 has an out of order section name 'JOURNAL OF APPLIED PHYSICS. Objects must be sorted by section name'

我已经使用不区分大小写的比较了，为什么这不起作用？帮助

======= 用于获取数据的代码=======

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

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Article" 
                                          inManagedObjectContext:SharedMOC];

[fetchRequest setEntity:entity];

NSSortDescriptor *journalSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Journal" 
                                                                     ascending:ascending 
                                                                      selector:@selector(caseInsensitiveCompare:)];

NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:journalSortDescriptor,  nil];

[fetchRequest setSortDescriptors:sortDescriptors];

NSFetchedResultsController *a = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                                                    managedObjectContext:SharedMOC 
                                                                      sectionNameKeyPath:[self selectedSortSection]
                                                                               cacheName:cacheName];

Answer 1

我的直觉说不是：

[fetchRequest setSortDescriptors:[self getSortDescriptor]];

你应该写：

[fetchRequest setSortDescriptors:sortDescriptors];