- (BOOL)isEqual:(id)object {  
// By default, if two variables point to the same object in memory, it should always be // equal  
    if (object == self) {  
        return YES;   
    }  
    if (![object isKindOfClass:[MyItem class]]) {   
        return NO;  
    }  
    MyItem *myItem = (MyItem *)object;  
    return [myItem.identifier isEqual:self.identifier];   
}