Odoo 19 – Critical Studio Error (Product / Purchase Tab) – Expert Needed

I am looking for a highly experienced Odoo 19 specialist (SaaS, Studio) who can reliably diagnose and fix complex Studio/ORM issues.

Problem (concise):
When saving products, a server error occurs:
ValueError: Cannot convert product.template.product_variant_id to SQL because it is not stored
This error blocks changes in the Purchase tab.

Environment:

Odoo 19 (SaaS)

Odoo Studio only (no custom modules, no server access)

Model: product.template

Task:

Identify and fix the root cause (Studio field, related field, stored/non-stored relation, trigger, domain, view, or action)

Ensure products can be saved without errors and the Purchase tab works normally

No workarounds – a clean, stable solution is required

Requirements (mandatory):

Proven experience with Odoo 19 Studio (SaaS)

Strong understanding of Odoo ORM, stored vs. non-stored fields, related fields, views & actions

Ability to correctly interpret Odoo server tracebacks

No beginners, no guessing, no trial-and-error

Working style:

Short, precise, solution-focused

Clear explanation of what is changed/removed and why

Fix must be tested live

Please apply only if you are fully confident and have solved similar Odoo Studio issues before.