Fixed #25715 -- Fixed Model.refresh_from_db() with ForeignKey w/on_delete=SET_NULL.

4 files changed, 16 insertions, 1 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 1dbf0e52e2..149b0e5a42 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -592,7 +592,7 @@ class Model(six.with_metaclass(ModelBase)):
                 rel_instance = getattr(self, field.get_cache_name())
                 local_val = getattr(db_instance, field.attname)
                 related_val = None if rel_instance is None else getattr(rel_instance, field.target_field.attname)
-                if local_val != related_val:
+                if local_val != related_val or (local_val is None and related_val is None):
                     del self.__dict__[field.get_cache_name()]
         self._state.db = db_instance._state.db
 
diff --git a/docs/releases/1.8.7.txt b/docs/releases/1.8.7.txt
index acc82f1581..8ffae59b21 100644
--- a/docs/releases/1.8.7.txt
+++ b/docs/releases/1.8.7.txt
@@ -36,3 +36,6 @@ Bugfixes
   :class:`~django.contrib.postgres.fields.DateTimeRangeField` (:ticket:`24937`).
 
 * Fixed the exact lookup of ``ArrayField`` (:ticket:`25666`).
+
+* Fixed ``Model.refresh_from_db()`` updating of ``ForeignKey`` fields with
+  ``on_delete=models.SET_NULL`` (:ticket:`25715`).
diff --git a/tests/basic/models.py b/tests/basic/models.py
index 0e85087d32..91fbe7d648 100644
--- a/tests/basic/models.py
+++ b/tests/basic/models.py
@@ -34,6 +34,7 @@ class SelfRef(models.Model):
         null=True, blank=True,
         related_name='+',
     )
+    article = models.ForeignKey(Article, models.SET_NULL, null=True, blank=True)
 
     def __str__(self):
         # This method intentionally doesn't work for all cases - part
diff --git a/tests/basic/tests.py b/tests/basic/tests.py
index 84033da43e..c67f78926f 100644
--- a/tests/basic/tests.py
+++ b/tests/basic/tests.py
@@ -765,6 +765,17 @@ class ModelRefreshTests(TestCase):
         self.assertEqual(a2.pub_date, pub_date)
         self.assertEqual(a2._state.db, "default")
 
+    def test_refresh_fk_on_delete_set_null(self):
+        a = Article.objects.create(
+            headline='Parrot programs in Python',
+            pub_date=datetime(2005, 7, 28),
+        )
+        s1 = SelfRef.objects.create(article=a)
+        a.delete()
+        s1.refresh_from_db()
+        self.assertIsNone(s1.article_id)
+        self.assertIsNone(s1.article)
+
     def test_refresh_no_fields(self):
         a = Article.objects.create(pub_date=self._truncate_ms(datetime.now()))
         with self.assertNumQueries(0):