gistfile1.m

void RMPrintError(NSError* error){
	NSArray* errors = [[error userInfo] valueForKey:@"NSDetailedErrors"];
	if(errors != nil){
		for(NSError* nestedError in errors){
			NSLog(@"%@", [nestedError userInfo]);
		}
	}
	else{
		NSLog(@"%@", error);
	}
	NSLog(@"\n");
}

@implementation NSManagedObjectContext (MyContext)

- (id)fetchRequestWithEntity:(NSEntityDescription*)entity predicateOrNil:(NSPredicate*)predicate{
	NSFetchRequest* request = [[NSFetchRequest alloc] init];
	[request setEntity:entity];
	[request setPredicate:predicate];
	NSError* error = nil;
	id result = [self executeFetchRequest:request error:&error];
	[request release];
	if(result == nil){
		RMPrintError(error);
		NSException* exception = [NSException exceptionWithName:RMFetchRequestException
														 reason:[NSString stringWithFormat:@"Cannot fetch %@", [entity name]]
													   userInfo:[error userInfo]];
		@throw exception;
	}
	
	return result;
}

@end