bool showAlert = YES;

        Category *category = [[curArticle articleCategories] anyObject];

        if (category.in_app_purchase.length > 0) {

            if ([category.in_app_purchase isEqualToString:@"frei"]) {
                category.in_app_purchase = nil;
                [self doArticle:curArticle];
                showAlert = NO;
            }
            else {
                for (SKProduct *product in [WoerterbuchInAppPurchase instance].purchasedProducts) {
                    if ([product.productIdentifier isEqualToString:[NSString stringWithFormat:@"com.mattnail.buchlexikon.%@",category.in_app_purchase]]) {
                        category.purchased = [NSNumber numberWithBool:YES];
                        [self doArticle:curArticle];
                        showAlert = NO;
                        break;
                    }
                }
            }
        }
        else {
            [self doArticle:curArticle];
            showAlert = NO;
        }

        if (showAlert) {
            UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Hinweis" message:[NSString stringWithFormat:@"Bitte kaufen Sie das Paket %@ um diesen Artikel anzusehen",category.title] delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil] autorelease];
            [alert show];
        }

        [[DataManager instance] saveContext];