Question

I am trying to work with NSPredicates. But it always give me back the same array. Here you can see my predicate.

NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"whichAlbum.album_id == %d", AlbumId];
    [request setEntity:[NSEntityDescription entityForName:@"Picture" inManagedObjectContext:self.genkDatabase.managedObjectContext]];
    [request setPredicate:predicate];

Also when I try it hardcoded. It gives back the same array.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"whichAlbum.album_id == 5"];

My database model is:

And here you can see how I put data in my database for entity Picture.

+ (Picture *)pictureWithGenkInfo:(NSDictionary *)genkInfo
          inManagedObjectContext:(NSManagedObjectContext *)context
                     withAlbumId:(int)albumId
                   withPictureId:(int)pictureId;
{

    Picture *picture = nil;

    picture = [NSEntityDescription insertNewObjectForEntityForName:@"Picture"
                                          inManagedObjectContext:context];
    picture.url                     = [genkInfo objectForKey:PICTURES_URL];
    picture.pic_album_id            = [NSNumber numberWithInt:albumId];
    picture.picture_id              = [NSNumber numberWithInt:pictureId];


    return picture;
}

Anybody can help me ?

Kind regards
EDIT

  for (NSDictionary *genkInfo in albums ) {
        albumId++;
        Album *album = [Album albumWithGenkInfo:genkInfo inManagedObjectContext:document.managedObjectContext withAlbumId:albumId];
        for (NSDictionary *genkInfo2 in pictures ) {
            pictureId++;
            Picture *pic = [Picture pictureWithGenkInfo:genkInfo2 inManagedObjectContext:document.managedObjectContext withAlbumId:albumId withPictureId:pictureId];
            [album addPicturesObject:pic]; // this method should be automatically generated
        }
        pictureId = 0;
        // table will automatically update due to NSFetchedResultsController's observing of the NSMOC
    }

Answer 1

Better, assuming the value for AlbumId is some kind of number primitive:

old style:
[NSPredicate predicateWithFormat:@"whichAlbum == %@", [NSNumber numberWithInt:AlbumId]];
modern style: (xcode 4.5)
[NSPredicate predicateWithFormat:@"whichAlbum == %@", @(albumId)];

As it looks like predicateWithFormat: might only generate proper predicates with %@ and @K in its format strings.

Best: Assuming you have access to the Album managed object you are trying to match try this:

[NSPredicate predicateWithFormat:@"whichAlbum == %@", album];

Match to the object, not one of its properties