[ADD] domain to create only not linked orders

models/res_partner_contract_annex.py

@@ -8,7 +8,12 @@ class ContractOrderAnnex(models.Model):
     _description = "Contract Order Annex"
 
     name = fields.Char(string="Name", help="The Number of Annex")
-    order_id = fields.Many2one("sale.order", string="Order", required=True)
+    order_id = fields.Many2one(
+        "sale.order",
+        string="Order",
+        domain=[("contract_annex_id", "=", False)],
+        required=True,
+    )
     contract_id = fields.Many2one(
         "res.partner.contract", string="Contract", readonly=True
     )
@@ -25,6 +30,7 @@ class ContractOrderAnnex(models.Model):
             record.name = "{contract}--{annex}".format(
                 contract=contract_number, annex=annex_number
             )
+        record.order_id.contract_annex_id = record.id
 
         return record
 

models/sale_order.py

@@ -2,25 +2,25 @@ from odoo import api, fields, models
 
 
 class SaleOrder(models.Model):
-    _inherit = 'sale.order'
+    _inherit = "sale.order"
 
-    delivery_time = fields.Integer(
-        string='Delivery Time',
-        default=45,
+    delivery_time = fields.Integer(string="Delivery Time", default=45,)
+    contract_annex_id = fields.Many2one(
+        "res.partner.contract.annex", string="Contract Annex", readonly=True,
     )
     # Extend default field
     payment_term_id = fields.Many2one(
-        'account.payment.term',
-        domain=lambda self: [('id', 'in', self._get_payment_terms())]
+        "account.payment.term",
+        domain=lambda self: [("id", "in", self._get_payment_terms())],
     )
 
     @api.multi
     def _get_payment_terms(self):
         ref = self.env.ref
         terms = (
-            ref('client_contracts.payment_term_prepaid').id,
-            ref('client_contracts.payment_term_postpayment').id,
-            ref('client_contracts.payment_term_partial_2').id,
-            ref('client_contracts.payment_term_partial_3').id,
+            ref("client_contracts.payment_term_prepaid").id,
+            ref("client_contracts.payment_term_postpayment").id,
+            ref("client_contracts.payment_term_partial_2").id,
+            ref("client_contracts.payment_term_partial_3").id,
         )
         return terms

views/sale_order.xml

@@ -10,6 +10,7 @@
             
             <xpath expr="//field[@name='payment_term_id']" position="after">
                 <field name="delivery_time"/>
+                <field name="contract_annex_id"/>
             </xpath>
             
         </field>