Inventory in several places: your warehouse, your supplier's and how much to restock

Your store has a warehouse with your best sellers. The rest of the catalogue is in your supplier's warehouse, which ships it to you in one or two days. If the product page only looks at your stock, everything you don't have shows as “out of stock” and the sale goes to another store. If you sell without checking anything, you promise lead times you cannot meet.

Between those two extremes lies hybrid inventory: selling with your stock and your suppliers' stock, with clear rules and telling the customer the truth in each case. And, in parallel, deciding how much to restock of what you do keep yourself.

The three situations of a product

Out of the box, PrestaShop only knows your stock and a global “Allow ordering of out-of-stock products” option. With that option enabled the customer can buy any quantity even if your supplier has none either, and with it disabled you lose everything your supplier does have.

Purchase rules, not an on/off switch

What you need is to decide per product (or per combination) which rules apply:

• Do not sell more than the sum of your stock and the supplier's.
• Allow unlimited purchases when the supplier has unlimited availability (made to order, for example).
• Block the purchase when the supplier has very few units left, because in practice their data takes time to update and those last units may not be there.

Make a clear distinction between “unlimited stock” and “a specific quantity”: they are not the same, and treating them alike is a common source of overselling.

Messages that don't mislead

The customer has the right to know when their order will arrive, and information about delivery times is part of the pre-contractual information. If a product ships from the supplier's warehouse, say so on the product page and in the cart: available quantity, lead time and, if you wish, different messages for “plenty available” and “you are ordering more than there is”.

Supplier data should arrive on its own

Hybrid inventory only works if the supplier's stock is reasonably up to date. Typing it in by hand does not scale. The usual options:

1. The supplier (or your system) sends quantities to your store through a protected endpoint.
2. You import their stock file with a scheduled task.
3. A connector reads their API.

In any case, keep the supplier data separate from your stock. Merging them into a single number stops you from knowing what you have and what depends on someone else.

How much to restock of what you keep

The other half of the problem is your own warehouse. The usual way to decide how much to order is to look at average sales and multiply by the days until the next restock. It works, except for one detail that spoils it: the days when the product could not be bought.

If a product sold out at the start of the period and you took a long time to restock it, the average says it sells little. That is not true: it could not be sold. The same happens with the days it was disabled. A sensible forecast:

• Excludes out-of-stock and disabled days from the average.
• Uses a specific period (last season, the last campaign) and not the whole history, which would make you restock what sold years ago.
• Calculates demand up to the date you choose and subtracts current stock: what is missing is what you order.
• Filters by supplier, so you can prepare each purchase order separately.
• Takes into account launches and special promotions, which skew the average.

How the two fit together

With hybrid inventory, your warehouse holds what turns over and the supplier covers the rest. The restocking forecast tells you which products deserve a place in your warehouse and in what quantity; supplier stock prevents the rest from showing as out of stock. Review each season which products switch sides: what starts selling a lot to order can move to your own stock, and what sits idle in your warehouse can move to order-only.

A note on versions

Purchase rules hook into the cart and the product page, which have changed quite a lot between PrestaShop versions. Some supplier stock solutions are now written only for PrestaShop 9. If you are still on an old version, that is one more reason to plan the upgrade before complicating your stock logic.

Checklist

• Separate your stock from supplier stock.
• Define purchase rules per product or combination.
• Show real lead times and availability on the product page and in the cart.
• Offer an enquiry option for what cannot be bought.
• Automate the arrival of supplier stock.
• Calculate restocking excluding out-of-stock days.

Frequently asked questions

Can I use supplier stock if I have a physical shop? Yes, but remember that what is in your physical shop is also stock that can be bought at the counter. If the physical and online shops share stock, synchronise those two first before adding the supplier's.

How often should supplier data be updated? As often as its turnover requires. For products that sell out quickly, several times a day; for slow-moving catalogue items, once a day is usually enough.

How to solve it in PrestaShop

The hybrid physical and external inventory management module decides whether a product can be bought based on the supplier stock you give it, with three built-in rules that you choose for each product or combination, messages per language on the product page and in the cart, an “I want to ask” button with an enquiry log and a token-protected endpoint so the supplier can send their quantities; it requires PrestaShop 9.0 or later. The stock requirements calculation module calculates how much to restock using sales from the period you choose, excluding out-of-stock or disabled days, by supplier and by combination, and exports the requirements to CSV.