Hi  Ra_one_1_11,

There is already a compute field 'sale_order_count' in 'res.partner' which shows the number of SO created for the partner.

Please Check,

https://github.com/odoo/odoo/blob/15.0/addons/sale/models/res_partner.py

Hello,

You have to write the compute method for get the sale orders in partner form view.

shivoham.odoo@gmail.com