Fixed #34840 -- Avoided casting string base fields on PostgreSQL.

Thanks Alex Vandiver for the report.

Regression in 09ffc5c1212d4ced58b708cbbf3dfbfb77b782ca.

1 files changed, 36 insertions, 0 deletions

diff --git a/tests/constraints/tests.py b/tests/constraints/tests.py
index 55397449d9..e1b95baf60 100644
--- a/tests/constraints/tests.py
+++ b/tests/constraints/tests.py
@@ -995,6 +995,42 @@ class UniqueConstraintTests(TestCase):
             exclude={"name"},
         )
 
+    def test_validate_nullable_textfield_with_isnull_true(self):
+        is_null_constraint = models.UniqueConstraint(
+            "price",
+            "discounted_price",
+            condition=models.Q(unit__isnull=True),
+            name="uniq_prices_no_unit",
+        )
+        is_not_null_constraint = models.UniqueConstraint(
+            "price",
+            "discounted_price",
+            condition=models.Q(unit__isnull=False),
+            name="uniq_prices_unit",
+        )
+
+        Product.objects.create(price=2, discounted_price=1)
+        Product.objects.create(price=4, discounted_price=3, unit="ng/mL")
+
+        msg = "Constraint “uniq_prices_no_unit” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            is_null_constraint.validate(
+                Product, Product(price=2, discounted_price=1, unit=None)
+            )
+        is_null_constraint.validate(
+            Product, Product(price=2, discounted_price=1, unit="ng/mL")
+        )
+        is_null_constraint.validate(Product, Product(price=4, discounted_price=3))
+
+        msg = "Constraint “uniq_prices_unit” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            is_not_null_constraint.validate(
+                Product,
+                Product(price=4, discounted_price=3, unit="μg/mL"),
+            )
+        is_not_null_constraint.validate(Product, Product(price=4, discounted_price=3))
+        is_not_null_constraint.validate(Product, Product(price=2, discounted_price=1))
+
     def test_name(self):
         constraints = get_constraints(UniqueConstraintProduct._meta.db_table)
         expected_name = "name_color_uniq"