Fixed #37057 -- Adjusted UniqueConstraint handling of UNKNOWN condition.

When we adjusted UNKNOWN handling for CheckConstraint in refs #33996 we assumed
that all usage of Q.check would benefit from this approach.

However while CHECK constraints enforcement do ignore conditions involving NULL
that resolve to UNKNOWN it's not the case for other type of constraints such as
UNIQUE ones.

Given how UNKNOWN should be treated depends on the callers context it appears
that a better strategy for COALESCE wrapping is to force them to apply it if
necessary.

Thanks Drew Shapiro for the report.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/constraints/tests.py b/tests/constraints/tests.py
index 39b170125f..0c10429c22 100644
--- a/tests/constraints/tests.py
+++ b/tests/constraints/tests.py
@@ -1297,6 +1297,19 @@ class UniqueConstraintTests(TestCase):
         with self.assertRaisesMessage(ValidationError, msg):
             constraint.validate(Product, Product(price=None))
 
+    @skipUnlessDBFeature("supports_comparing_boolean_expr")
+    def test_validate_nullable_condition(self):
+        GeneratedFieldStoredProduct.objects.create(name="Product", price=42)
+        constraint = models.UniqueConstraint(
+            fields=["name"],
+            name="uniq_name_for_positive_price",
+            condition=models.Q(price__gt=0),
+        )
+        constraint.validate(
+            GeneratedFieldStoredProduct,
+            GeneratedFieldStoredProduct(name="Product", price=None),
+        )
+
     def test_name(self):
         constraints = get_constraints(UniqueConstraintProduct._meta.db_table)
         expected_name = "name_color_uniq"