創建實體之間的關係

Question

我有一個ViewController與保存在NSMutableArray中的播放列表。我使用Singleton將所選對象傳遞給SecondViewController。

optionsSingle.selectedRowNow = [devices objectAtIndex:indexPath.row]; 

在SecondViewController中，我添加了歌曲。我如何關聯傳遞給SecondViewController的optionsSingle.selectedRowNow與保存的歌曲？我會很感激代碼片段/示例，因爲我一直在努力掙扎幾個小時，並且一直沒能在互聯網上找到有用的東西。

歌曲添加方法：

NSManagedObjectContext *context = 
[appDelegate managedObjectContext]; 
NSManagedObject *newManagedObject; 
newManagedObject = (Songs*)[NSEntityDescription insertNewObjectForEntityForName:@"Songs" inManagedObjectContext:context]; 
NSDate *today= [NSDate date]; 

[newManagedObject setValue:video.author forKey:@"author"]; 
[newManagedObject setValue:video.videoid forKey:@"link"]; 
[newManagedObject setValue:video.title forKey:@"songName"]; 
[newManagedObject setValue:today forKey:@"created"]; 

實體

songs.h

@class Playlists; 

@interface Songs : NSManagedObject 

@property (nonatomic, retain) NSString * author; 
@property (nonatomic, retain) NSDate * created; 
@property (nonatomic, retain) NSString * link; 
@property (nonatomic, retain) NSString * songName; 
@property (nonatomic, retain) NSSet *songs; 
@end 

@interface Songs (CoreDataGeneratedAccessors) 

- (void)addSongsObject:(Playlists *)value; 
- (void)removeSongsObject:(Playlists *)value; 
- (void)addSongs:(NSSet *)values; 
- (void)removeSongs:(NSSet *)values; 

@end 

playlists.h

@class Songs; 

@interface Playlists : NSManagedObject 

@property (nonatomic, retain) NSString * playlistName; 
@property (nonatomic, retain) NSSet *list; 
@end 

@interface Playlists (CoreDataGeneratedAccessors) 

- (void)addListObject:(Songs *)value; 
- (void)removeListObject:(Songs *)value; 
- (void)addList:(NSSet *)values; 
- (void)removeList:(NSSet *)values; 

@end 

Answer 1

[optionsSingle.selectedRowNow addListObject:newManagedObject]; 

這會從'singleton'獲取播放列表並將關係添加到歌曲（追加到當前關係中的任何歌曲）。