核心数据一对多关系，在NSSet上分配，获取，谓词

Question

嗨， 我希望获取所有具有playlist_index = 1的歌曲。我创建了一对多关系并生成了访问器。 但是，当我通过谓词获取歌曲时，尽管我已经向许多歌曲添加了相同的播放列表，但它总是只给我一首歌曲。通过将纯NSManagedObject转换为coredata生成的模型对象，这就是我向歌曲添加播放列表的方式。

-(void) addPlaylistToAudio {
 // Audio Coredata Model
   Audio *audioManagedObject = [self getAudioManagedObject:self.artist];

   PlaylistModel *playlistObj = [self.arrayPlaylist objectAtIndex:indexPath.row];
// Playlist Coredata Model
    Playlist *playlistManagedObject = [self getPlaylistManagedObject:playlistObj];

  [audioManagedObject addPlaylist_relationObject:playlistManagedObject];
  [playlistManagedObject setAudio_relation:audioManagedObject];

   // PLEASE CHECK HERE IF I AM ADDING CORRECTLY

   NSManagedObjectContext *context = [[CoreDataHandler sharedInstance] 
   managedObjectContext];
   NSError *error = nil;

   if (![context save:&error]) {
   }
   else {
   }
  }

- (Audio *)getAudioManagedObject:(Artist *)artist {

// Create Predicate to fetch managed object.
   NSPredicate *predicate = [NSPredicate 
   predicateWithFormat:@"track_index == %ld",artist.track_index];

// Get Predicate array of managed object.
   NSArray *arrayAudioManagedObject = [[CoreDataHandler sharedInstance] 
   fetchAudioManagedObjectsWithPredicate:predicate havePredicate:TRUE];

// Managed object.
  Audio *audioManagedObject = [arrayAudioManagedObject lastObject];

  return audioManagedObject;
}


-(Playlist *)getPlaylistManagedObject:(PlaylistModel *)playlist {

// Create Predicate to fetch managed object.
   NSPredicate *predicate = [NSPredicate 
predicateWithFormat:@"playlist_index == %ld",playlist.playlist_index];

// Get Predicate array of managed object.
  NSArray *arrayPlaylistManagedObject = [[CoreDataHandler sharedInstance] 
fetchPlaylistManagedObjectsWithPredicate:predicate havePredicate:TRUE];

// Managed object.
   Playlist *playlistManagedObject = [arrayPlaylistManagedObject 
lastObject];

   return playlistManagedObject;
}

获取：

NSPredicate *predicate_audio = [NSPredicate predicateWithFormat:@"ANY playlist_relation.playlist_index == %ld",self.playlistInfo.playlist_index];
NSArray *arraySongsManagedObject = [[CoreDataHandler sharedInstance] fetchAudioManagedObjectsWithPredicate:predicate_audio havePredicate:TRUE];

 

Answer 1

我认为ANY只会返回一个符合您条件的结果，您真正需要的是SUBQUERY，您可以在其中用以下内容替换委托：

let predicate_audio = NSPredicate(format: "SUBQUERY(playlist_realtion, $x, $x.playlist_index == %ld).@count > 0", self.playlistInfo.playlist_index)

或在Objective-C

中

NSPredicate *predicate_audio = [NSPredicate predicateWithFormat:@"SUBQUERY(playlist_realtion, $x, $x.playlist_index == %ld).@count > 0", self.playlistInfo.playlist_index]

请注意，$x只是代表每个元素关系的占位符。

链接：

NSPredicate with SubQuery

http://davidchuprogramming.blogspot.com/2016/10/one-to-many-relationship-and-subquery.html

让我知道它是否对您有用