add fields in existing one to many field odoo
For that you need to inherit sale.order.line object and use xpath to display in sale order form view.
In PY:-
class SaleOrderLine(models.Model):
_inherit = 'sale.order.line'
x_field = fields.Char('X Field')
In Xml:-
<record model="ir.ui.view" id="sale_order_view_inherit">
<field name="name">sale.order.view.inherit1</field>
<field name="model">sale.order</field>
<field name="inherit_id" ref="sale.view_order_form"/>
<field name="arch" type="xml">
<xpath expr="/form/sheet/notebook/page/field[@name='order_line']/tree/field[@name='name']" position="after">
<field name="x_field"/>
</xpath>
</field>
</record>
This fields shows after Description in the sale order line.
Hope it will helps you.
Thanks,