[FIX] fields: default to ondelete='cascade' for required m2o fields on transient

TransientModel (wizards) can be annoying because if they have required
many2one fields, those fields will default to `ondelete='restrict'`,
preventing user to delete the comodel records without deleting the
transient model records first.

To improve such case, we default to `ondelete='cascade'` for required
many2one field on a TransientModel (unless specified otherwise)

closes odoo/odoo#36738

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

odoo/addons/test_new_api/models.py

@@ -594,6 +594,14 @@ class RequiredM2O(models.Model):
     bar = fields.Many2one('res.country', required=True)
 
 
+class RequiredM2OTransient(models.TransientModel):
+    _name = 'test_new_api.req_m2o_transient'
+    _description = 'Transient Model with Required Many2one'
+
+    foo = fields.Many2one('res.currency', required=True, ondelete='restrict')
+    bar = fields.Many2one('res.country', required=True)
+
+
 class Attachment(models.Model):
     _name = 'test_new_api.attachment'
     _description = 'Attachment'

odoo/addons/test_new_api/tests/test_new_fields.py

@@ -1929,3 +1929,25 @@ class TestRequiredMany2one(common.TransactionCase):
 
         with self.assertRaises(ValueError):
             field._setup_regular_base(Model)
+
+
+class TestRequiredMany2oneTransient(common.TransactionCase):
+
+    def test_explicit_ondelete(self):
+        field = self.env['test_new_api.req_m2o_transient']._fields['foo']
+        self.assertEqual(field.ondelete, 'restrict')
+
+    def test_implicit_ondelete(self):
+        field = self.env['test_new_api.req_m2o_transient']._fields['bar']
+        self.assertEqual(field.ondelete, 'cascade')
+
+    def test_explicit_set_null(self):
+        Model = self.env['test_new_api.req_m2o_transient']
+        field = Model._fields['foo']
+
+        # invalidate registry to redo the setup afterwards
+        self.registry.registry_invalidated = True
+        self.patch(field, 'ondelete', 'set null')
+
+        with self.assertRaises(ValueError):
+            field._setup_regular_base(Model)

odoo/fields.py

@@ -2306,7 +2306,14 @@ class Many2one(_Relational):
         # 3) The ondelete attribute is explicitly defined as 'set null' for a required m2o,
         #    this is considered a programming error.
         if not self.ondelete:
-            self.ondelete = 'restrict' if self.required else 'set null'
+            comodel = model.env[self.comodel_name]
+            if model.is_transient() and not comodel.is_transient():
+                # Many2one relations from TransientModel Model are annoying because
+                # they can block deletion due to foreign keys. So unless stated
+                # otherwise, we default them to ondelete='cascade'.
+                self.ondelete = 'cascade' if self.required else 'set null'
+            else:
+                self.ondelete = 'restrict' if self.required else 'set null'
         if self.ondelete == 'set null' and self.required:
             raise ValueError(
                 "The m2o field %s of model %s is required but declares its ondelete policy "
@@ -2318,11 +2325,6 @@ class Many2one(_Relational):
         comodel = model.env[self.comodel_name]
         if not model.is_transient() and comodel.is_transient():
             raise ValueError('Many2one %s from Model to TransientModel is forbidden' % self)
-        if model.is_transient() and not comodel.is_transient():
-            # Many2one relations from TransientModel Model are annoying because
-            # they can block deletion due to foreign keys. So unless stated
-            # otherwise, we default them to ondelete='cascade'.
-            self.ondelete = self.ondelete or 'cascade'
         return super(Many2one, self).update_db(model, columns)
 
     def update_db_column(self, model, column):