Fixed #29641 -- Added support for unique constraints in Meta.constraints.

This constraint is similar to Meta.unique_together but also allows
specifying a name.

Co-authored-by: Ian Foote <python@ian.feete.org>

tests/constraints/tests.py

@@ -1,3 +1,4 @@
+from django.core.exceptions import ValidationError
 from django.db import IntegrityError, connection, models
 from django.db.models.constraints import BaseConstraint
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
@@ -50,3 +51,42 @@ class CheckConstraintTests(TestCase):
         if connection.features.uppercases_column_names:
             expected_name = expected_name.upper()
         self.assertIn(expected_name, constraints)
+
+
+class UniqueConstraintTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.p1 = Product.objects.create(name='p1')
+
+    def test_repr(self):
+        fields = ['foo', 'bar']
+        name = 'unique_fields'
+        constraint = models.UniqueConstraint(fields=fields, name=name)
+        self.assertEqual(
+            repr(constraint),
+            "<UniqueConstraint: fields=('foo', 'bar') name='unique_fields'>",
+        )
+
+    def test_deconstruction(self):
+        fields = ['foo', 'bar']
+        name = 'unique_fields'
+        check = models.UniqueConstraint(fields=fields, name=name)
+        path, args, kwargs = check.deconstruct()
+        self.assertEqual(path, 'django.db.models.UniqueConstraint')
+        self.assertEqual(args, ())
+        self.assertEqual(kwargs, {'fields': tuple(fields), 'name': name})
+
+    def test_database_constraint(self):
+        with self.assertRaises(IntegrityError):
+            Product.objects.create(name=self.p1.name)
+
+    def test_model_validation(self):
+        with self.assertRaisesMessage(ValidationError, 'Product with this Name already exists.'):
+            Product(name=self.p1.name).validate_unique()
+
+    def test_name(self):
+        constraints = get_constraints(Product._meta.db_table)
+        expected_name = 'unique_name'
+        if connection.features.uppercases_column_names:
+            expected_name = expected_name.upper()
+        self.assertIn(expected_name, constraints)