Prevent to delete shipment costs if they are not cancelled or draft

modules/account_stock_shipment_cost/account.py

@@ -7,6 +7,7 @@ from sql.functions import CharLength
 
 from trytond.i18n import gettext
 from trytond.model import Index, ModelSQL, ModelView, Workflow, fields
+from trytond.model.exceptions import AccessError
 from trytond.modules.company.model import CompanyValueMixin
 from trytond.modules.product import price_digits, round_price
 from trytond.pool import Pool, PoolMeta
@@ -334,6 +335,16 @@ class ShipmentCost(Workflow, ModelSQL, ModelView):
                     company=values.get('company', default_company)).get()
         return super().create(vlist)
 
+    @classmethod
+    def delete(cls, shipment_costs):
+        for shipment_cost in shipment_costs:
+            if shipment_cost.state not in {'cancelled', 'draft'}:
+                raise AccessError(
+                    gettext('account_stock_shipment_cost'
+                        '.msg_shipment_cost_delete_cancel',
+                        shipment_cost=shipment_cost.rec_name))
+        super().delete(shipment_costs)
+
 
 class ShipmentCost_Shipment(ModelSQL):
     __name__ = 'account.shipment_cost-stock.shipment.out'

modules/account_stock_shipment_cost/message.xml

@@ -9,5 +9,8 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.message" id="msg_shipment_cost_post_same_parties">
             <field name="text">The shipment "%(shipment)s" of shipment cost "%(shipment_cost)s" has already shipment cost from the same party "%(other)s".</field>
         </record>
+        <record model="ir.message" id="msg_shipment_cost_delete_cancel">
+            <field name="text">To delete shipment cost "%(shipment_cost)s" you must cancel it.</field>
+        </record>
     </data>
 </tryton>

modules/account_stock_shipment_cost/tests/scenario_account_stock_shipment_cost.rst

@@ -219,6 +219,13 @@ Check shipment cost::
     >>> shipment2.cost
     Decimal('5.0000')
 
+Can not delete posted shipment cost::
+
+    >>> shipment_cost1.delete()
+    Traceback (most recent call last):
+        ...
+    AccessError: ...
+
 Cancel shipment cost remove the price::
 
     >>> shipment_cost1.click('cancel')
@@ -234,3 +241,7 @@ Check shipment cost::
     >>> shipment2.reload()
     >>> shipment2.cost
     Decimal('0.0000')
+
+Can delete cancelled shipment cost::
+
+    >>> shipment_cost1.delete()