[FIX] base: fallback on model_id to fill related field

Scenario:

- go to a model in technical
- create a new field and set "Related Field" to id

=> error "Unknown field name 'id' in related field 'id'" because we
get the field in self.model which is not present in the form view.

Fix:

Fallback to self.model_id.model as was the case before 16.0 commit:
76f699ca0b

Note: without the change, the added tests fails with:

  Warning Unknown field name 'id' in related field 'id'
  AssertionError: False != 'integer

opw-3138440
closes #112495

closes odoo/odoo#140583

X-original-commit: aa406352541abd8bbf188da84fc4e370029ffc12
Signed-off-by: Rémy Voet (ryv) <ryv@odoo.com>
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

odoo/addons/base/models/ir_model.py

@@ -632,7 +632,7 @@ class IrModelFields(models.Model):
         """ Return the ``ir.model.fields`` record corresponding to ``self.related``. """
         names = self.related.split(".")
         last = len(names) - 1
-        model_name = self.model
+        model_name = self.model or self.model_id.model
         for index, name in enumerate(names):
             field = self._get(model_name, name)
             if not field:

odoo/addons/base/tests/test_ir_model.py

@@ -4,7 +4,7 @@
 from psycopg2 import IntegrityError
 
 from odoo.exceptions import ValidationError
-from odoo.tests.common import TransactionCase, HttpCase, tagged
+from odoo.tests.common import Form, TransactionCase, HttpCase, tagged
 from odoo.tools import mute_logger
 from odoo import Command
 
@@ -424,6 +424,19 @@ class TestIrModel(TransactionCase):
         self.assertEqual(monetary_field.currency_field, "x_good_currency",
                          "The currency field in monetary should have x_good_currency as name")
 
+@tagged('-at_install', 'post_install')
+class TestIrModelEdition(TransactionCase):
+    def test_new_ir_model_fields_related(self):
+        """Check that related field are handled correctly on new field"""
+        model = self.env['ir.model'].create({
+            'name': 'Bananas',
+            'model': 'x_bananas'
+        })
+        with self.debug_mode():
+            form = Form(self.env['ir.model.fields'].with_context(default_model_id=model.id))
+            form.related = 'id'
+            self.assertEqual(form.ttype, 'integer')
+
 @tagged('test_eval_context')
 class TestEvalContext(TransactionCase):