How does the ordering process "come together"

Hi everyone. I'm developing my own plugin to allow a Warehouse Location to be shown on the paperwork we use to pick the stock to facilitate speeding location of the stock. It's going well but I need to input information into TABLE_ORDERS_PRODUCTS and I can't find the appropriate php file where this happens for each order. Could anyone point me in the right direction? I've tried using Developers Toolkit but it hasn't been very useful.
Many thanks in anticipation.
Philip

I see you've been posting the same question in the Super Orders support thread.

My question is: WHY do you think you need to put ANYTHING in the orders_products table?

If your warehouse-location-info is already in another table, and especially if it's already related to your products in some way, then why don't you just tell whatever tool you use to print your warehouse sheets (I'm guessing Super Orders since that's where you started posting) to look up that data from those other tables, and output it that way.
There's no need to store warehouse location info in "yet another" place in the database, if it's already available in the database somewhere.

In short, you've been posting with a technical "solution" already madeup in your mind. I'm not sure it's the best solution. I don't want to give you answers that push you further in the wrong direction. So let's back WAY up and start with what is the business problem you're trying to solve, and what data/tools you already have available. And work out the best solution from there.

I take your point Dr Byte. I know the direction in which I should be going - I just can't get my head around the code.

BTW I'm not in the habit of multiple posting - I just realised this was the more appropriate place.

What I should have done yesterday was explain what I think the best solution to my problem is and seek help with that. Unfortunately embarrassment/pride got in the way. I'm over that now.
I should say at the outset that I am new to php - in fact this is my first "real" project.
I do indeed use super orders but a lot of the grunt work is done by ZC files, in this case order.php. I've put my data in warehouse_location in the PRODUCTS table. It seems to me that as data from the orders_products table, for each item I need to call warehouse location from TABLE_PRODUCTS. The best common link would be product_model. The code to achieve that escapes me and any help would be much appreciated.
Regards
Philip

The best common link would be the products_id.

SELECT warehouse_location from products where products_id = 33;

select op.*, p.warehouse_location from orders_products op, products p 
where op.products_id=p.products_id
and orders_id=5;