I'm trying to duplicate the manfacturers function in oscommerce and I'm stuck in writing to database

the manufacturers function in oscommerce is proving to be very useful feature, I'm using it to filter products by their conditions. I then wanted to be able to have another of such functionalities to filter my products ones more I have dublicated all the files and code snippets related to manufacturers and called it 'byproducts'; so far I managed to get most of it working:

In the admin area I can add the new byproducts (manufacturers) - and then I can view the combo box in the view pages (exactly like having a second manufacturers combo box, but with different content)

Now the problem is when trying to assign the byproducts to a new product. Again I managed to place the option into the .../admin/categories.php - so the user can type the product name, select their manufacturer and select the 'byproduct' such the sameway.

But when I add the product to the database, everthing gets added to the products table apart from the byproducts_id

I made sure that I have made the right changes to the database. this is the code that I think should be running when I add a new product

From .../admin/categories.php

tep_db_query("insert into " . TABLE_PRODUCTS . " (products_quantity, products_model,products_image, products_price, products_date_added, products_date_available, prod开发者_开发技巧ucts_weight, products_status, products_tax_class_id, manufacturers_id, byproducts_id) 
values ('" . tep_db_input($product['products_quantity']) . "', '" . tep_db_input($product['products_model']) . "', '" . tep_db_input($product['products_image']) . "', '" . tep_db_input($product['products_price']) . "',  now(), " . (empty($product['products_date_available']) ? "null" : "'" . tep_db_input($product['products_date_available']) . "'") . ", '" . tep_db_input($product['products_weight']) . "', '0', '" . (int)$product['products_tax_class_id'] . "', '" . (int)$product['manufacturers_id'] . "', '" . (int)$product['byproducts_id'] . "')");
            $dup_products_id = tep_db_insert_id();

This code does not give any errors, as I said I am aware that I needed to add code to other files, so every file that mentioned manufacturer, I coped the coped/pasted the code and changed the manufacturer to byproducts - But I have a strong feeling that the problem is not in the above code but somewhere else

thanks a lot for your help