Ticket #13771: t13771_1.diff

django/db/models/fields/related.py

@@ -789 +789 @@
         if not value:
             return
 
-        qs = self.rel.to._default_manager.filter(**{self.rel.field_name:value})
+        db = model_instance._state.db
+        if db is None:
+            db = router.db_for_write(model_instance.__class__, instance=model_instance)
+        qs = self.rel.to._default_manager.using(db).filter(**{self.rel.field_name:value})
         qs = qs.complex_filter(self.rel.limit_choices_to)
         if not qs.exists():
             raise exceptions.ValidationError(self.error_messages['invalid'] % {

tests/regressiontests/multiple_database/tests.py

@@ -64 +64 @@
             title="Dive into Python"
         )
 
+    def test_foreign_key_validation(self):
+        """
+        ForeignKey validation when both object and related object were created
+        on another database wouldn't try to look up related object on the default database
+        """
+        # Create a book on the second database
+        george = Person.objects.using('other').create(name="George Vilches")
+        book = Book.objects.using('other').create(title="Pro Django",
+                                                  published=datetime.date(2008, 12, 16),
+                                                  editor=george)
+
+        #if validation fails full_clean raises ValidationError
+        self.assertEqual(book.full_clean(), None)
 
     def test_other_creation(self):
         "Objects created on another database don't leak onto the default database"