创建与实体之间的关系

Question

我有一个带有播放列表的 ViewController，它保存在 NSMutableArray 中。我使用 Singleton 将所选对象传递给 SecondViewController。

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

在 SecondViewController 中，我添加了歌曲。如何将传递给 SecondViewController 的 optionsSingle.selectedRowNow 与保存的歌曲相关联？我会很感激使用代码 sn-p/sample，因为我已经为此苦苦挣扎了几个小时，并且无法在互联网上找到有用的东西。

添加歌曲方法：

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"];

实体

歌曲.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

播放列表.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];

这会从“单例”中获取播放列表并将关系添加到歌曲中（附加到当前关系中的任何歌曲）。