Partner VAT Unique

This module adds a new option in Odoo's Settings that lets you decide whether VAT numbers must be unique across contacts. You will find the checkbox labelled "Unique VAT Constraint" in the Contacts settings section of the general Settings screen.

When the option is switched on, Odoo checks every contact you save. If you try to save a contact whose VAT number is already used by another contact, Odoo stops you and shows an error saying that the VAT already exists in another partner.

• The check only applies to contacts that have a VAT number filled in; contacts without a VAT are never considered duplicates.
• Contacts that are children of another company (for example, a person linked to a parent company) are skipped, so the rule applies to the main contact records.
• The VAT field is no longer copied when you duplicate a contact, which helps avoid accidental duplicates.

The setting is stored as a system parameter, so it applies to the whole database once enabled. The module extends the res.partner model and the res.config.settings model, and adds a setting block to the existing configuration form.