[FIX] mrp: handle the case of empty routings

Before, when the routing of a production order was empty (no operations),
it got into an inconsistent state (you click on "plan" and nothing happens).

Empty routings were used before to do subcontracting or 2-steps inventeory
(we did not set any operations on the routing but we set a location).

Here, we change the related routing field on the production order into a
calculated field which becomes empty when the routing has no operations.
This way, the "produce" button is displayed (as for production orders
without routing) and working/

This is a temporary patch to workaround the issuein a stable release.
In master, we might remove the location on routing and place it on the
workcenters and put a constraint that does not allow an empty routing.

addons/mrp/models/mrp_production.py

@@ -94,7 +94,7 @@ class MrpProduction(models.Model):
         help="Bill of Materials allow you to define the list of required raw materials to make a finished product.")
     routing_id = fields.Many2one(
         'mrp.routing', 'Routing',
-        readonly=True, related='bom_id.routing_id', store=True,
+        readonly=True, compute='_compute_routing', store=True,
         help="The list of operations (list of work centers) to produce the finished product. The routing "
              "is mainly used to compute work center costs during operations and to plan future loads on "
              "work centers based on production planning.")
@@ -152,6 +152,15 @@ class MrpProduction(models.Model):
     priority = fields.Selection([('0', 'Not urgent'), ('1', 'Normal'), ('2', 'Urgent'), ('3', 'Very Urgent')], 'Priority',
                                 readonly=True, states={'confirmed': [('readonly', False)]}, default='1')
 
+    @api.multi
+    @api.depends('bom_id.routing_id', 'bom_id.routing_id.operation_ids')
+    def _compute_routing(self):
+        for production in self:
+            if production.bom_id.routing_id.operation_ids:
+                production.routing_id = production.bom_id.routing_id.id
+            else:
+                production.routing_id = False
+
     @api.multi
     @api.depends('workorder_ids')
     def _compute_workorder_count(self):
@@ -243,10 +252,6 @@ class MrpProduction(models.Model):
         self.location_src_id = self.picking_type_id.default_location_src_id.id or location.id
         self.location_dest_id = self.picking_type_id.default_location_dest_id.id or location.id
 
-    @api.onchange('bom_id')
-    def onchange_bom_id(self):
-        self.routing_id = self.bom_id.routing_id.id
-
     @api.model
     def create(self, values):
         if not values.get('name', False) or values['name'] == _('New'):

addons/mrp/tests/test_order.py

@@ -332,3 +332,16 @@ class TestMrpOrder(TestMrpCommon):
         production_2.action_assign()
         # check sub product availability state is assigned
         self.assertEqual(production_2.availability, 'assigned', 'Production order should be availability for assigned state')
+
+    def test_empty_routing(self):
+        """ Check what happens when you work with an empty routing"""
+        routing = self.env['mrp.routing'].create({'name': 'Routing without operations',
+                                        'location_id': self.warehouse_1.wh_input_stock_loc_id.id,})
+        self.bom_3.routing_id = routing.id
+        production = self.env['mrp.production'].create({'name': 'MO test',
+                                           'product_id': self.product_6.id,
+                                           'product_qty': 3,
+                                           'bom_id': self.bom_3.id,
+                                           'product_uom_id': self.product_6.uom_id.id,})
+        self.assertEqual(production.routing_id.id, False, 'The routing field should be empty on the mo')
+        self.assertEqual(production.move_raw_ids[0].location_id.id, self.warehouse_1.wh_input_stock_loc_id.id, 'Raw moves start location should have altered.')