我想要一个变量 NSSet 照片，它将照片随机存储在我的 Xcode xcdatamodel 中。我知道 NSSet 用于存储随机对象，但有没有办法将 NSSet 更改为 NSArray 或跟踪 NSSet 变量中的序列插入？
文章.h
@property (nonatomic, retain) NSSet *photos;
文章.m
RKManagedObjectMapping *_mapping = (RKManagedObjectMapping*)[RKManagedObjectMapping generatedManagedObjectMappingFromClass:[self class] keyUnderscored:NO excludesProperties:[NSArray arrayWithObjects:@"attachments", @"videos", @"photos", nil]];
[_mapping mapKeyPath:@"photos.photo" toRelationship:@"photos" withMapping:(RKManagedObjectMapping*)[BTAttachment rkObjectMapping]];
[_mapping mapKeyPath:@"attachments.attachment" toRelationship:@"attachments" withMapping:(RKManagedObjectMapping*)[BTAttachment rkObjectMapping]];
[更新]：
我意识到即使我使用
[_model.photos allObjects] objectAtIndex:0]
每次刷新时，0 索引仍在变化。