[4.2.x] Fixed #34291 -- Fixed Meta.constraints validation crash on UniqueConstraint with ordered expressions.

Thanks Dan F for the report.

Bug in 667105877e6723c6985399803a364848891513cc.
Backport of 2b1242abb3989f5d74e787b09132d01bcbee5b55 from main

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/constraints/tests.py b/tests/constraints/tests.py
index 5a498f0d73..223b4b3cd5 100644
--- a/tests/constraints/tests.py
+++ b/tests/constraints/tests.py
@@ -672,6 +672,29 @@ class UniqueConstraintTests(TestCase):
             exclude={"name"},
         )
 
+    def test_validate_ordered_expression(self):
+        constraint = models.UniqueConstraint(
+            Lower("name").desc(), name="name_lower_uniq_desc"
+        )
+        msg = "Constraint “name_lower_uniq_desc” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(
+                UniqueConstraintProduct,
+                UniqueConstraintProduct(name=self.p1.name.upper()),
+            )
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name="another-name"),
+        )
+        # Existing instances have their existing row excluded.
+        constraint.validate(UniqueConstraintProduct, self.p1)
+        # Unique field is excluded.
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name=self.p1.name.upper()),
+            exclude={"name"},
+        )
+
     def test_validate_expression_condition(self):
         constraint = models.UniqueConstraint(
             Lower("name"),