Use UICollectionView and NSFetchedResultsController doesn't save - iphone

Question

I'm using a project find on github that lets me use NSFetchedResultsController and UICollectionView, the project is this
in my project i have a Core Data with two Entity, Element and Document, there is a relationship one to many between Element and Document, so an Element can have more Document, but a Document can have only one Element, then i do this in the AppDelegate:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
ElementViewController *elementView = [[ElementViewController alloc] initWithNibName:#"ElementViewController" bundle:nil];
elementView.managedObjectContext = self.managedObjectContext;
DocumentViewController *documentView = [[DocumentViewController alloc] initWithNibName:#"DocumentViewController" bundle:nil];
documentView.managedObjectContext = self.managedObjectContext;
elementView.documentView = documentView;
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:elementView];
self.window.rootViewController = navController;
[self.window makeKeyAndVisible];
return YES;
}
this is the App delegate, then in ElementViewController i have a UICollectionView with NSFetchedResultsController, and all works ok, when i select a UICollectionViewCell i open the DocumentViewController:
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
self.documentView.element = [self.fetchedResultsController objectAtIndexPath:indexPath];
[self.navigationController pushViewController:self.documentView animated:YES];
}
then this is my DocumentViewController.h:
#import <UIKit/UIKit.h>
#import "Element.h"
#interface DocumentViewController : UIViewController <NSFetchedResultsControllerDelegate>
#property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
#property (weak, nonatomic) IBOutlet UICollectionView *collectionView;
#property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;
#property (strong, nonatomic) Element *element;
#end
And also here i have the NSFetchedResultsController, the filter in the predicate for the Element title:
- (NSFetchedResultsController *)fetchedResultsController
{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Document" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"docDate" ascending:NO];
NSArray *sortDescriptors = #[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"SUBQUERY(element, $b, $b.name == %#).#count > 0", self.element.name]];
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
return _fetchedResultsController;
}
and then i have add also this:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self reloadCollectionView];
[self addDocument];
}
- (void)reloadTableView
{
self.fetchedResultsController = nil; //Because not search every time for different Element
NSError *error;
if (![[self fetchedResultsController] performFetch:&error]) {
NSLog(#"Error in search %#, %#", error, [error userInfo]);
} else {
[self.collectionView reloadData];
}
}
then in the viewWillAppear there is the addDocument method:
- (void)addDocument
{
Document *document = (Document *)[NSEntityDescription
insertNewObjectForEntityForName:#"Document"
inManagedObjectContext:self.managedObjectContext];
[document setDocName:[title contents]];
[document setElement:self.element]; //here the app crash
}
and i receive these error:
CoreData: error: Serious application error. Exception was caught during Core Data change processing. This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification. Can't perform collection evaluate with non-collection object. with userInfo (null)
2013-01-25 10:28:56.392 App[383:c07] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Can't perform collection evaluate with non-collection object.'
anyone can help me?
EDIT:
This is the NSManagedObjectClass:
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#class Document;
#interface Element : NSManagedObject
#property (nonatomic, retain) NSString * dateFormat;
#property (nonatomic, retain) NSString * dateFormat2;
#property (nonatomic, retain) id img;
#property (nonatomic, retain) NSDate * imgDate;
#property (nonatomic, retain) NSString * imgUrl;
#property (nonatomic, retain) NSString * language;
#property (nonatomic, retain) NSString * name;
#property (nonatomic, retain) NSString * name2;
#property (nonatomic, retain) NSString * pathDocuments;
#property (nonatomic, retain) NSNumber * releaseDateWeek;
#property (nonatomic, retain) NSNumber * type;
#property (nonatomic, retain) NSSet *documents;
#end
#interface Element (CoreDataGeneratedAccessors)
- (void)addDocumentsObject:(Document *)value;
- (void)removeDocumentsObject:(Document *)value;
- (void)addDocuments:(NSSet *)values;
- (void)removeDocuments:(NSSet *)values;
#end
#interface ImageToDataTransformer : NSValueTransformer {
}
#end
Document.h
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#class Element;
#interface Document : NSManagedObject
#property (nonatomic, retain) NSDate * docDate;
#property (nonatomic, retain) id docImage;
#property (nonatomic, retain) NSString * docName;
#property (nonatomic, retain) NSString * docPath;
#property (nonatomic, retain) NSNumber * docSize;
#property (nonatomic, retain) NSString * docUrl;
#property (nonatomic, retain) NSNumber * isDownloading;
#property (nonatomic, retain) NSNumber * isStored;
#property (nonatomic, retain) NSNumber * pageNumber;
#property (nonatomic, retain) NSString * password;
#property (nonatomic, retain) NSNumber * progressBar;
#property (nonatomic, retain) Element *element;
#end

Answer 1

The problem looks to be that that in:
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"SUBQUERY(element, $b, $b.name == %#).#count > 0", self.element.name]];
'element' does not resolve to a collection (as required by SUBQUERY), but merely a single object.
See: http://developer.apple.com/library/Mac/#documentation/Cocoa/Reference/Foundation/Classes/NSExpression_Class/Reference/NSExpression.html