[4.2.x] Fixed #34319 -- Fixed Model.validate_constraints() crash on ValidationError with no code.

Thanks Mateusz Kurowski for the report.

Regression in 667105877e6723c6985399803a364848891513cc.
Backport of 2fd755b361d3da2cd0440fc9839feb2bb69b027b from main

1 files changed, 4 insertions, 1 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 8c8a74158d..493831759a 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1444,7 +1444,10 @@ class Model(AltersData, metaclass=ModelBase):
                 try:
                     constraint.validate(model_class, self, exclude=exclude, using=using)
                 except ValidationError as e:
-                    if e.code == "unique" and len(constraint.fields) == 1:
+                    if (
+                        getattr(e, "code", None) == "unique"
+                        and len(constraint.fields) == 1
+                    ):
                         errors.setdefault(constraint.fields[0], []).append(e)
                     else:
                         errors = e.update_error_dict(errors)