Fixed #28974 -- Made refresh_from_db() hint routers about its instance.

django/db/models/base.py

@@ -590,8 +590,8 @@ class Model(metaclass=ModelBase):
                     'Found "%s" in fields argument. Relations and transforms '
                     'are not allowed in fields.' % LOOKUP_SEP)
 
-        db = using if using is not None else self._state.db
-        db_instance_qs = self.__class__._base_manager.using(db).filter(pk=self.pk)
+        hints = {'instance': self}
+        db_instance_qs = self.__class__._base_manager.db_manager(using, hints=hints).filter(pk=self.pk)
 
         # Use provided fields, if not set then reload all non-deferred fields.
         deferred_fields = self.get_deferred_fields()

tests/multiple_database/tests.py

@@ -2,6 +2,7 @@ import datetime
 import pickle
 from io import StringIO
 from operator import attrgetter
+from unittest.mock import Mock
 
 from django.contrib.auth.models import User
 from django.contrib.contenttypes.models import ContentType
@@ -103,6 +104,14 @@ class QueryTestCase(TestCase):
         self.assertEqual(dive.title, "Dive into Python (on default)")
         self.assertEqual(dive._state.db, "default")
 
+    def test_refresh_router_instance_hint(self):
+        router = Mock()
+        router.db_for_read.return_value = None
+        book = Book.objects.create(title='Dive Into Python', published=datetime.date(1957, 10, 12))
+        with self.settings(DATABASE_ROUTERS=[router]):
+            book.refresh_from_db()
+        router.db_for_read.assert_called_once_with(Book, instance=book)
+
     def test_basic_queries(self):
         "Queries are constrained to a single database"
         dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))