Fixed #27599 -- Fixed Field.__str__() crash for fields not attached to models.

1 files changed, 6 insertions, 1 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 340e6a41b7..f1f68dbe7a 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -186,7 +186,12 @@ class Field(RegisterLookupMixin):
         self.error_messages = messages
 
     def __str__(self):
-        """ Return "app_label.model_label.field_name". """
+        """
+        Return "app_label.model_label.field_name" for fields attached to
+        models.
+        """
+        if not hasattr(self, 'model'):
+            return super(Field, self).__str__()
         model = self.model
         app = model._meta.app_label
         return '%s.%s.%s' % (app, model._meta.object_name, self.name)