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salesdiscountV18
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Benjamin Waroquier

Hello,

I am experiencing an issue on Odoo v18 (Enterprise, Odoo.sh).

When I set a discount (%) on a sales order line and then modify only the quantity, the discount is automatically reset to 0.

Steps to reproduce:

  1. Create a quotation
  2. Add a product
  3. Enter a discount (e.g. 10%)
  4. Save
  5. Change only the quantity on the same line

Result: the discount is reset to 0

Expected: the discount should remain unchanged if only the quantity is modified

This behavior is problematic for our users, as they often adjust quantities after applying commercial discounts.

I found a similar issue reported on OCB (issue #1300), so I’m wondering:

  • Is this a known bug in Odoo 18?
  • Is there a standard setting or workaround to prevent this?
  • Has anyone implemented a clean fix (without heavy customization)?

Any feedback would be greatly appreciated.

Thank you!

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Codesphere Tech
Best Answer

Hello,
It is due to Pricelist on Sale order.
Method: def _compute_discount(self):
Explanation:
When you change a Quantity, Odoo automatically re-calculates the line to check if the Pricelist has a specific rule for that new amount. Since your manual discount isn't a "rule" in the Pricelist, Odoo resets the field to 0% to match its official records.

Hope this helps
Thanks
info@codespheretech.in

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Jainesh Shah(Aktiv Software)
Best Answer

Hello Benjamin Waroquier,

This behavior usually occurs due to the Pricelist configuration.

When a Pricelist is applied to the Sales Order, Odoo recalculates the price and discount based on the pricelist rules whenever you modify certain fields like quantity. As a result, the manually entered discount gets reset and replaced by the discount defined in the pricelist.

However, if no pricelist is applied, Odoo will keep the manually entered discount unchanged when you modify the quantity.

So this is not necessarily a bug, but rather expected behavior when a pricelist with discount rules is active.

You may check:

  • If a pricelist is applied on the Sales Order
  • Whether the pricelist contains discount rules
  • If the "Discount Policy" in the pricelist affects how discounts are applied

As a workaround, you can:

  • Remove the pricelist, or
  • Adjust the pricelist configuration depending on your needs

If you have any questions, feel free to reach out.

Hope this helps!

 

Thanks and Regards,

Email: odoo@aktivsoftware.com

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Cybrosys Techno Solutions Pvt.Ltd
Best Answer

Hi,

Changing the quantity on a sale order line triggers the product_id_change onchange method, which recomputes the unit price and the discount based on the pricelist rules for the new quantity. This is by design in Odoo's core because pricelist rules can be quantity-dependent (e.g., 10% discount for qty > 10). However, the side effect is that any manually entered discount is wiped out, which is the problem you are hitting.

Workarounds and fixes:
Option 1 — OCA Module (cleanest, no heavy customization)
sale_order_qty_change_no_recompute (https://apps.odoo.com/apps/modules/17.0/sale_order_qty_change_no_recompute)— this module prevents recomputing the unit price, discount, and pricelist item fields if only the quantity on a sales order line has changed.
Note: It is not available for Odoo 18. So, you must migrate it with small changes.

Option 2 — Use Pricelists instead of manual discounts

If your team always applies the same discount to a customer, set it directly on the customer pricelist rather than entering it manually on each line. Pricelist-based discounts survive quantity changes because the onchange recomputes them correctly.


Hope it helps

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