contract/agreement_sale/models/agreement.py

# Copyright (C) 2018 - TODAY, Open Source Integrators
# License AGPL-3.0 or later (http://www.gnu.org/licenses/lgpl).

from odoo import fields, models


class Agreement(models.Model):
    _inherit = 'agreement'

    sale_id = fields.Many2one('sale.order', string='Sales Order')