带有NSSortDescriptor的NSFetchedResultsController一对一

Question

想要使用NSSortDescriptor在NSFetchedResultsController中使用一对一关系的名称进行排序。在这里我的代码

NSFetchRequest <studentDetail *> *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:[studentDetail entityName]]; 

NSSortDescriptor *sortDescriptorForSchoolName = [NSSortDescriptor sortDescriptorWithKey:NSStringFromSelector(@selector(schoolName)) 
                      ascending:YES 
                       selector:@selector(localizedCaseInsensitiveCompare:)]; 

NSSortDescriptor *sortDescriptorForSchool = [NSSortDescriptor sortDescriptorWithKey:NSStringFromSelector(@selector(school)) 
                       ascending:YES]; 

[fetchRequest setSortDescriptors:@[sortDescriptorForSchool, sortDescriptorForSchoolName]]; 

[fetchRequest setFetchBatchSize:4]; 

NSManagedObjectContext *mainContext = [[coreDataManager sharedManager] managedObjectContext]; 

NSFetchedResultsController *FRC = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                         managedObjectContext:mainContext 
                         sectionNameKeyPath:nil 
                            cacheName:nil]; 

[FRC setDelegate: self]; 

NSError *fetchError = nil; 

if (![FRC performFetch: &fetchError]) 
    NSLog(@"fetch error: %@", fetchError); 

[self setStudentDetailFetchedResultsController: FRC]; 

实例DB格式：

1. 学校和学生的实体名称。
2. 与学生一对多的学校关系。
3. 共有4所学校。每所学校有4名学生。
4. 现在我想显示所有学生名单的名称升序排序。

在UITableView我正在显示学生的详细信息。有一个选项可以按排序school实体进行排序。在我的FRC有studentDetail。我怎样才能将这些细节与FRC分类？

从studentDetail实体与school有一对一的关系。

更新

school entity一对多

school1 
relationship 
    ->student1 
    ->student2 
    ->student3 
    ->student4 
school2 
relationship 
    ->student5 
    ->student6 
    ->student7 
    ->student8 
school3 
relationship 
    ->student9 
    ->student10 
    ->student11 
    ->student12 
school4 
relationship 
    ->student13 
    ->student14 
    ->student15 
    ->student16 

student entity一对一

student1 
relationship 
    ->school1 
student2 
relationship 
    ->school1 
student3 
relationship 
    ->school1 
student4 
relationship 
    ->school1 
student5 
relationship 
    ->school2 
student6 
relationship 
    ->school2 
student7 
relationship 
    ->school2 
student8 
relationship 
    ->school2 
student9 
relationship 
    ->school3 
student10 
relationship 
    ->school3 
student11 
relationship 
    ->school3 
student12 
relationship 
    ->school3 
student13 
relationship 
    ->school4 
student14 
relationship 
    ->school4 
student15 
relationship 
    ->school4 
student16 
relationship 
    ->school4 

Got answer from感谢@RunLoop。但是这需要一些我想要的改变。

正如我在我的代码提到了排序NSStringFromSelector(@selector(school))一样，例如：如果我在实体更改任何名称，而不是[NSSortDescriptor sortDescriptorWithKey:@"school.schoolName" ascending:YES]

[NSSortDescriptor sortDescriptorWithKey[NSString stringWithFormat:@"%K.%K", NSStringFromSelector(@selector(school)), NSStringFromSelector(@selector(schoolName))] ascending:YES]如果我用这种方法，在功能，这是显示警告和静态的school.schoolName没有。那可能吗？ 我试过这个方法，NSPredicate没有显示任何警告。我应该如何解决这个问题？

Answer 1

下面的代码将获取的学生，通过schoolName下令然后通过studentName：

NSFetchRequest *fr = [NSFetchRequest fetchRequestWithEntityName:@"Student"]; 
NSSortDescriptor *schoolNameSD = [NSSortDescriptor sortDescriptorWithKey:@"school.schoolName" ascending:YES]; 
NSSortDescriptor *studentNameSD = [NSSortDescriptor sortDescriptorWithKey:@"studentName" ascending:YES]; 
fr.sortDescriptors = @[schoolNameSD, studentNameSD]; 

NSManagedObjectContext *moc = [[coreDataManager sharedManager] managedObjectContext]; 


NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fr 
                      managedObjectContext:moc 
                      sectionNameKeyPath:nil 
                        cacheName:nil]; 
[frc performFetch:nil]; 

如果你只是想通过studentName进行排序，只需删除schoolNameSD并要求FRC再次进行抓取。