将NSManagedObjects添加到一对多关系中(Adding NSManagedObjects to a one-to-many relationship)

 我有很多关系，例如一个学生有很多课程。 
 
 为什么在运行以下代码时_classes中没有新的Cls对象？ 然而，当我关闭应用程序并重新打开它时。 
 
 作为一个后续问题，如何在添加新的类之后立即获取新的类列表？ 
 
NSMutableSet* classes = [student mutableSetValueForKey:@"classes"];
NSManagedObject* cls = [NSEntityDescription insertNewObjectForEntityForName:@"Cls" inManagedObjectContext:context];
[cls setValue:name forKey:@"name"];
[student addClassesObject:cls];

NSError* err;
[context save:&err];

NSMutableSet* _classes = [student mutableSetValueForKey:@"classes"];
 
 这就是我的addClassesObject：操作的样子（由XCode自动生成） 
 
- (void)addClassesObject:(Cls*)cls
{

}
 
 谢谢！ 

I have a to-many relationship, e.g. A student has many classes.
 
Why is it when I run the following code _classes does NOT have the new Cls object in it? Yet when I close the app and reopen it does.
 
And as a follow up question, How would I get the new list of classes right after adding adding a new one?
 
NSMutableSet* classes = [student mutableSetValueForKey:@"classes"];
NSManagedObject* cls = [NSEntityDescription insertNewObjectForEntityForName:@"Cls" inManagedObjectContext:context];
[cls setValue:name forKey:@"name"];
[student addClassesObject:cls];

NSError* err;
[context save:&err];

NSMutableSet* _classes = [student mutableSetValueForKey:@"classes"];
 
And this is what my addClassesObject: operation looks like (auto generated by XCode)
 
- (void)addClassesObject:(Cls*)cls
{

}
 
Thank you!

原文：https://stackoverflow.com/questions/10989983