Question

I am quite new to Core Data, and actually Objective-C as a whole, so I hope I am phrasing this correctly, I have been able to store and retrieve data using Core Data, but I am struggling to loop through a result set,

// read the data
NSFetchRequest *req = [[NSFetchRequest alloc]init];
[req setEntity:[NSEntityDescription entityForName:@"Card" inManagedObjectContext:app.managedObjectContext]];
//[req setPredicate:[NSPredicate predicateWithFormat:@"cardID == %@", @"1"]];
NSArray *crd = [[app.managedObjectContext executeFetchRequest:req error:nil] lastObject];

for(Card *card in crd){
    NSLog(@"%@",card.backImageURL);
}

I keep getting this error though when I try to run the app,

2012-10-16 11:37:29.407 Core test[925:17903] -[Card countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0x962f5c0
2012-10-16 11:37:29.408 Core test[925:17903] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Card countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0x962f5c0'

I am sure it is something extremely simple but for some reason I can’t seem to pinpoint the problem.

Answer 1

Instead of

NSArray *crd = [[app.managedObjectContext executeFetchRequest:req error:nil] lastObject];

it should be

NSArray *crd = [app.managedObjectContext executeFetchRequest:req error:nil];

If you are getting error, then you should use that error parameter –

NSError *error = nil;
NSArray *crd = [app.managedObjectContext executeFetchRequest:req error:&error];
if(error){
    NSLog(@"ERROR: %@", [error localizedDescription]);
}