Add modules agreement_account and agreement_sale

agreement_account/models/account_invoice.py

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*-
+# © 2017 Akretion (http://www.akretion.com)
+# @author: Alexis de Lattre <alexis.delattre@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from odoo import models, fields
+
+
+class AccountInvoice(models.Model):
+    _inherit = 'account.invoice'
+
+    sale_agreement_id = fields.Many2one(
+        'sale.agreement', string='Sale Agreement', ondelete='restrict',
+        readonly=True, states={'draft': [('readonly', False)]},
+        track_visibility='onchange')