executeFetchRequest：error获取请求必须具有实体

Question

我在搜索部分遇到错误。当我输入歌曲名称时，我应该在那里得到歌词但是收到错误说'executeFetchRequest：错误：获取请求必须有一个实体。'我使用了以下代码

-(void)findLyrics
       {
             LyricsAppDelegate *appDelegate = [[UIApplication sharedApplication] 
                              delegate];
NSManagedObjectContext *managedObjectContext = [appDelegate managedObjectContext];
NSEntityDescription *entityDesc = [NSEntityDescription    
entityForName:@"Lyrics"inManagedObjectContext:managedObjectContext];
NSManagedObject *LyricsObjectEnglish;
LyricsObjectEnglish = [NSEntityDescription      insertNewObjectForEntityForName:@"English_Songs"   
                                                inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; 

[request setEntity:entityDesc]; 
NSPredicate *pred = [NSPredicate predicateWithFormat:@"(MovieSongName = %@)",song_name.text];
[request setPredicate:pred];
NSManagedObject *matches = nil;
NSError *error;

NSArray *objects = [managedObjectContext executeFetchRequest:request error:&error];

if ([objects count] == 0) 
  {
    //status.text = @"No matches";
  } else {
   matches = [objects objectAtIndex:0];
   song_lyrics.text = [matches valueForKey:@"SongLyrics"];
   song_name.text = [matches valueForKey:@"MovieSongName"];
      // status.text = [NSString stringWithFormat:@"%d matches found", [objects count]];
  }
 [request release];
  }

任何身体请帮助..