django/tests/constraints/tests.py

from unittest import mock

from django.core.exceptions import ValidationError
from django.db import IntegrityError, connection, models
from django.db.models import F
from django.db.models.constraints import BaseConstraint, UniqueConstraint
from django.db.models.functions import Abs, Lower, Sqrt, Upper
from django.db.transaction import atomic
from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature

from .models import (
    ChildModel,
    ChildUniqueConstraintProduct,
    GeneratedFieldStoredProduct,
    GeneratedFieldVirtualProduct,
    JSONFieldModel,
    ModelWithDatabaseDefault,
    Product,
    UniqueConstraintConditionProduct,
    UniqueConstraintDeferrable,
    UniqueConstraintInclude,
    UniqueConstraintProduct,
)


def get_constraints(table):
    with connection.cursor() as cursor:
        return connection.introspection.get_constraints(cursor, table)


class BaseConstraintTests(SimpleTestCase):
    def test_constraint_sql(self):
        c = BaseConstraint(name="name")
        msg = "This method must be implemented by a subclass."
        with self.assertRaisesMessage(NotImplementedError, msg):
            c.constraint_sql(None, None)

    def test_contains_expressions(self):
        c = BaseConstraint(name="name")
        self.assertIs(c.contains_expressions, False)

    def test_create_sql(self):
        c = BaseConstraint(name="name")
        msg = "This method must be implemented by a subclass."
        with self.assertRaisesMessage(NotImplementedError, msg):
            c.create_sql(None, None)

    def test_remove_sql(self):
        c = BaseConstraint(name="name")
        msg = "This method must be implemented by a subclass."
        with self.assertRaisesMessage(NotImplementedError, msg):
            c.remove_sql(None, None)

    def test_validate(self):
        c = BaseConstraint(name="name")
        msg = "This method must be implemented by a subclass."
        with self.assertRaisesMessage(NotImplementedError, msg):
            c.validate(None, None)

    def test_default_violation_error_message(self):
        c = BaseConstraint(name="name")
        self.assertEqual(
            c.get_violation_error_message(), "Constraint “name” is violated."
        )

    def test_custom_violation_error_message(self):
        c = BaseConstraint(
            name="base_name", violation_error_message="custom %(name)s message"
        )
        self.assertEqual(c.get_violation_error_message(), "custom base_name message")

    def test_custom_violation_error_message_clone(self):
        constraint = BaseConstraint(
            name="base_name",
            violation_error_message="custom %(name)s message",
        ).clone()
        self.assertEqual(
            constraint.get_violation_error_message(),
            "custom base_name message",
        )

    def test_custom_violation_code_message(self):
        c = BaseConstraint(name="base_name", violation_error_code="custom_code")
        self.assertEqual(c.violation_error_code, "custom_code")

    def test_deconstruction(self):
        constraint = BaseConstraint(
            name="base_name",
            violation_error_message="custom %(name)s message",
            violation_error_code="custom_code",
        )
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.BaseConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs,
            {
                "name": "base_name",
                "violation_error_message": "custom %(name)s message",
                "violation_error_code": "custom_code",
            },
        )

    def test_name_required(self):
        msg = (
            "BaseConstraint.__init__() missing 1 required keyword-only argument: 'name'"
        )
        with self.assertRaisesMessage(TypeError, msg):
            BaseConstraint()


class CheckConstraintTests(TestCase):
    def test_eq(self):
        check1 = models.Q(price__gt=models.F("discounted_price"))
        check2 = models.Q(price__lt=models.F("discounted_price"))
        self.assertEqual(
            models.CheckConstraint(condition=check1, name="price"),
            models.CheckConstraint(condition=check1, name="price"),
        )
        self.assertEqual(
            models.CheckConstraint(condition=check1, name="price"), mock.ANY
        )
        self.assertNotEqual(
            models.CheckConstraint(condition=check1, name="price"),
            models.CheckConstraint(condition=check1, name="price2"),
        )
        self.assertNotEqual(
            models.CheckConstraint(condition=check1, name="price"),
            models.CheckConstraint(condition=check2, name="price"),
        )
        self.assertNotEqual(models.CheckConstraint(condition=check1, name="price"), 1)
        self.assertNotEqual(
            models.CheckConstraint(condition=check1, name="price"),
            models.CheckConstraint(
                condition=check1, name="price", violation_error_message="custom error"
            ),
        )
        self.assertNotEqual(
            models.CheckConstraint(
                condition=check1, name="price", violation_error_message="custom error"
            ),
            models.CheckConstraint(
                condition=check1,
                name="price",
                violation_error_message="other custom error",
            ),
        )
        self.assertEqual(
            models.CheckConstraint(
                condition=check1, name="price", violation_error_message="custom error"
            ),
            models.CheckConstraint(
                condition=check1, name="price", violation_error_message="custom error"
            ),
        )
        self.assertNotEqual(
            models.CheckConstraint(condition=check1, name="price"),
            models.CheckConstraint(
                condition=check1, name="price", violation_error_code="custom_code"
            ),
        )
        self.assertEqual(
            models.CheckConstraint(
                condition=check1, name="price", violation_error_code="custom_code"
            ),
            models.CheckConstraint(
                condition=check1, name="price", violation_error_code="custom_code"
            ),
        )

    def test_repr(self):
        constraint = models.CheckConstraint(
            condition=models.Q(price__gt=models.F("discounted_price")),
            name="price_gt_discounted_price",
        )
        self.assertEqual(
            repr(constraint),
            "<CheckConstraint: condition=(AND: ('price__gt', F(discounted_price))) "
            "name='price_gt_discounted_price'>",
        )

    def test_repr_with_violation_error_message(self):
        constraint = models.CheckConstraint(
            condition=models.Q(price__lt=1),
            name="price_lt_one",
            violation_error_message="More than 1",
        )
        self.assertEqual(
            repr(constraint),
            "<CheckConstraint: condition=(AND: ('price__lt', 1)) name='price_lt_one' "
            "violation_error_message='More than 1'>",
        )

    def test_repr_with_violation_error_code(self):
        constraint = models.CheckConstraint(
            condition=models.Q(price__lt=1),
            name="price_lt_one",
            violation_error_code="more_than_one",
        )
        self.assertEqual(
            repr(constraint),
            "<CheckConstraint: condition=(AND: ('price__lt', 1)) name='price_lt_one' "
            "violation_error_code='more_than_one'>",
        )

    def test_invalid_check_types(self):
        msg = "CheckConstraint.condition must be a Q instance or boolean expression."
        with self.assertRaisesMessage(TypeError, msg):
            models.CheckConstraint(condition=models.F("discounted_price"), name="check")

    def test_deconstruction(self):
        check = models.Q(price__gt=models.F("discounted_price"))
        name = "price_gt_discounted_price"
        constraint = models.CheckConstraint(condition=check, name=name)
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.CheckConstraint")
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {"condition": check, "name": name})

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_database_constraint(self):
        Product.objects.create(price=10, discounted_price=5)
        with self.assertRaises(IntegrityError):
            Product.objects.create(price=10, discounted_price=20)

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_database_constraint_unicode(self):
        Product.objects.create(price=10, discounted_price=5, unit="μg/mL")
        with self.assertRaises(IntegrityError):
            Product.objects.create(price=10, discounted_price=7, unit="l")

    @skipUnlessDBFeature(
        "supports_table_check_constraints", "can_introspect_check_constraints"
    )
    def test_name(self):
        constraints = get_constraints(Product._meta.db_table)
        for expected_name in (
            "price_gt_discounted_price",
            "constraints_product_price_gt_0",
        ):
            with self.subTest(expected_name):
                self.assertIn(expected_name, constraints)

    @skipUnlessDBFeature(
        "supports_table_check_constraints", "can_introspect_check_constraints"
    )
    def test_abstract_name(self):
        constraints = get_constraints(ChildModel._meta.db_table)
        self.assertIn("constraints_childmodel_adult", constraints)

    def test_validate(self):
        check = models.Q(price__gt=models.F("discounted_price"))
        constraint = models.CheckConstraint(condition=check, name="price")
        # Invalid product.
        invalid_product = Product(price=10, discounted_price=42)
        with self.assertRaises(ValidationError):
            constraint.validate(Product, invalid_product)
        with self.assertRaises(ValidationError):
            constraint.validate(Product, invalid_product, exclude={"unit"})
        # Fields used by the check constraint are excluded.
        constraint.validate(Product, invalid_product, exclude={"price"})
        constraint.validate(Product, invalid_product, exclude={"discounted_price"})
        constraint.validate(
            Product,
            invalid_product,
            exclude={"discounted_price", "price"},
        )
        # Valid product.
        constraint.validate(Product, Product(price=10, discounted_price=5))

    def test_validate_custom_error(self):
        check = models.Q(price__gt=models.F("discounted_price"))
        constraint = models.CheckConstraint(
            condition=check,
            name="price",
            violation_error_message="discount is fake",
            violation_error_code="fake_discount",
        )
        # Invalid product.
        invalid_product = Product(price=10, discounted_price=42)
        msg = "discount is fake"
        with self.assertRaisesMessage(ValidationError, msg) as cm:
            constraint.validate(Product, invalid_product)
        self.assertEqual(cm.exception.code, "fake_discount")

    def test_validate_boolean_expressions(self):
        constraint = models.CheckConstraint(
            condition=models.expressions.ExpressionWrapper(
                models.Q(price__gt=500) | models.Q(price__lt=500),
                output_field=models.BooleanField(),
            ),
            name="price_neq_500_wrap",
        )
        msg = f"Constraint “{constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(Product, Product(price=500, discounted_price=5))
        constraint.validate(Product, Product(price=501, discounted_price=5))
        constraint.validate(Product, Product(price=499, discounted_price=5))

    def test_validate_rawsql_expressions_noop(self):
        constraint = models.CheckConstraint(
            condition=models.expressions.RawSQL(
                "price < %s OR price > %s",
                (500, 500),
                output_field=models.BooleanField(),
            ),
            name="price_neq_500_raw",
        )
        # RawSQL can not be checked and is always considered valid.
        constraint.validate(Product, Product(price=500, discounted_price=5))
        constraint.validate(Product, Product(price=501, discounted_price=5))
        constraint.validate(Product, Product(price=499, discounted_price=5))

    @skipUnlessDBFeature("supports_comparing_boolean_expr")
    def test_validate_nullable_field_with_none(self):
        # Nullable fields should be considered valid on None values.
        constraint = models.CheckConstraint(
            condition=models.Q(price__gte=0),
            name="positive_price",
        )
        constraint.validate(Product, Product())

    @skipIfDBFeature("supports_comparing_boolean_expr")
    def test_validate_nullable_field_with_isnull(self):
        constraint = models.CheckConstraint(
            condition=models.Q(price__gte=0) | models.Q(price__isnull=True),
            name="positive_price",
        )
        constraint.validate(Product, Product())

    @skipUnlessDBFeature("supports_json_field")
    def test_validate_nullable_jsonfield(self):
        is_null_constraint = models.CheckConstraint(
            condition=models.Q(data__isnull=True),
            name="nullable_data",
        )
        is_not_null_constraint = models.CheckConstraint(
            condition=models.Q(data__isnull=False),
            name="nullable_data",
        )
        is_null_constraint.validate(JSONFieldModel, JSONFieldModel(data=None))
        msg = f"Constraint “{is_null_constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            is_null_constraint.validate(JSONFieldModel, JSONFieldModel(data={}))
        msg = f"Constraint “{is_not_null_constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            is_not_null_constraint.validate(JSONFieldModel, JSONFieldModel(data=None))
        is_not_null_constraint.validate(JSONFieldModel, JSONFieldModel(data={}))

    def test_validate_pk_field(self):
        constraint_with_pk = models.CheckConstraint(
            condition=~models.Q(pk=models.F("age")),
            name="pk_not_age_check",
        )
        constraint_with_pk.validate(ChildModel, ChildModel(pk=1, age=2))
        msg = f"Constraint “{constraint_with_pk.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint_with_pk.validate(ChildModel, ChildModel(pk=1, age=1))
        with self.assertRaisesMessage(ValidationError, msg):
            constraint_with_pk.validate(ChildModel, ChildModel(id=1, age=1))
        constraint_with_pk.validate(ChildModel, ChildModel(pk=1, age=1), exclude={"pk"})

    @skipUnlessDBFeature("supports_json_field")
    def test_validate_jsonfield_exact(self):
        data = {"release": "5.0.2", "version": "stable"}
        json_exact_constraint = models.CheckConstraint(
            condition=models.Q(data__version="stable"),
            name="only_stable_version",
        )
        json_exact_constraint.validate(JSONFieldModel, JSONFieldModel(data=data))

        data = {"release": "5.0.2", "version": "not stable"}
        msg = f"Constraint “{json_exact_constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            json_exact_constraint.validate(JSONFieldModel, JSONFieldModel(data=data))

    @skipUnlessDBFeature("supports_stored_generated_columns")
    def test_validate_generated_field_stored(self):
        self.assertGeneratedFieldIsValidated(model=GeneratedFieldStoredProduct)

    @skipUnlessDBFeature("supports_virtual_generated_columns")
    def test_validate_generated_field_virtual(self):
        self.assertGeneratedFieldIsValidated(model=GeneratedFieldVirtualProduct)

    def assertGeneratedFieldIsValidated(self, model):
        constraint = models.CheckConstraint(
            condition=models.Q(rebate__range=(0, 100)), name="bounded_rebate"
        )
        constraint.validate(model, model(price=50, discounted_price=20))

        invalid_product = model(price=1200, discounted_price=500)
        msg = f"Constraint “{constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(model, invalid_product)

        # Excluding referenced or generated fields should skip validation.
        constraint.validate(model, invalid_product, exclude={"price"})
        constraint.validate(model, invalid_product, exclude={"rebate"})

    def test_database_default(self):
        models.CheckConstraint(
            condition=models.Q(field_with_db_default="field_with_db_default"),
            name="check_field_with_db_default",
        ).validate(ModelWithDatabaseDefault, ModelWithDatabaseDefault())

        # Ensure that a check also does not silently pass with either
        # FieldError or DatabaseError when checking with a db_default.
        with self.assertRaises(ValidationError):
            models.CheckConstraint(
                condition=models.Q(
                    field_with_db_default="field_with_db_default", field="field"
                ),
                name="check_field_with_db_default_2",
            ).validate(
                ModelWithDatabaseDefault, ModelWithDatabaseDefault(field="not-field")
            )

        with self.assertRaises(ValidationError):
            models.CheckConstraint(
                condition=models.Q(field_with_db_default="field_with_db_default"),
                name="check_field_with_db_default",
            ).validate(
                ModelWithDatabaseDefault,
                ModelWithDatabaseDefault(field_with_db_default="other value"),
            )


class UniqueConstraintTests(TestCase):
    @classmethod
    def setUpTestData(cls):
        cls.p1 = UniqueConstraintProduct.objects.create(name="p1", color="red")
        cls.p2 = UniqueConstraintProduct.objects.create(name="p2")

    def test_eq(self):
        self.assertEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
        )
        self.assertEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
            mock.ANY,
        )
        self.assertNotEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
            models.UniqueConstraint(fields=["foo", "bar"], name="unique2"),
        )
        self.assertNotEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
            models.UniqueConstraint(fields=["foo", "baz"], name="unique"),
        )
        self.assertNotEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"), 1
        )
        self.assertNotEqual(
            models.UniqueConstraint(fields=["foo", "bar"], name="unique"),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_message="custom error",
            ),
        )
        self.assertNotEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_message="custom error",
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_message="other custom error",
            ),
        )
        self.assertEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_message="custom error",
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_message="custom error",
            ),
        )
        self.assertNotEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_code="custom_error",
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_code="other_custom_error",
            ),
        )
        self.assertEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_code="custom_error",
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                violation_error_code="custom_error",
            ),
        )

    def test_eq_with_condition(self):
        self.assertEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                condition=models.Q(foo=models.F("bar")),
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                condition=models.Q(foo=models.F("bar")),
            ),
        )
        self.assertNotEqual(
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                condition=models.Q(foo=models.F("bar")),
            ),
            models.UniqueConstraint(
                fields=["foo", "bar"],
                name="unique",
                condition=models.Q(foo=models.F("baz")),
            ),
        )

    def test_eq_with_deferrable(self):
        constraint_1 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="unique",
            deferrable=models.Deferrable.DEFERRED,
        )
        constraint_2 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="unique",
            deferrable=models.Deferrable.IMMEDIATE,
        )
        self.assertEqual(constraint_1, constraint_1)
        self.assertNotEqual(constraint_1, constraint_2)

    def test_eq_with_include(self):
        constraint_1 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="include",
            include=["baz_1"],
        )
        constraint_2 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="include",
            include=["baz_2"],
        )
        self.assertEqual(constraint_1, constraint_1)
        self.assertNotEqual(constraint_1, constraint_2)

    def test_eq_with_opclasses(self):
        constraint_1 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="opclasses",
            opclasses=["text_pattern_ops", "varchar_pattern_ops"],
        )
        constraint_2 = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="opclasses",
            opclasses=["varchar_pattern_ops", "text_pattern_ops"],
        )
        self.assertEqual(constraint_1, constraint_1)
        self.assertNotEqual(constraint_1, constraint_2)

    def test_eq_with_expressions(self):
        constraint = models.UniqueConstraint(
            Lower("title"),
            F("author"),
            name="book_func_uq",
        )
        same_constraint = models.UniqueConstraint(
            Lower("title"),
            "author",
            name="book_func_uq",
        )
        another_constraint = models.UniqueConstraint(
            Lower("title"),
            name="book_func_uq",
        )
        self.assertEqual(constraint, same_constraint)
        self.assertEqual(constraint, mock.ANY)
        self.assertNotEqual(constraint, another_constraint)

    def test_eq_with_nulls_distinct(self):
        constraint_1 = models.UniqueConstraint(
            Lower("title"),
            nulls_distinct=False,
            name="book_func_nulls_distinct_uq",
        )
        constraint_2 = models.UniqueConstraint(
            Lower("title"),
            nulls_distinct=True,
            name="book_func_nulls_distinct_uq",
        )
        constraint_3 = models.UniqueConstraint(
            Lower("title"),
            name="book_func_nulls_distinct_uq",
        )
        self.assertEqual(constraint_1, constraint_1)
        self.assertEqual(constraint_1, mock.ANY)
        self.assertNotEqual(constraint_1, constraint_2)
        self.assertNotEqual(constraint_1, constraint_3)
        self.assertNotEqual(constraint_2, constraint_3)

    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_repr_with_condition(self):
        constraint = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="unique_fields",
            condition=models.Q(foo=models.F("bar")),
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: fields=('foo', 'bar') name='unique_fields' "
            "condition=(AND: ('foo', F(bar)))>",
        )

    def test_repr_with_deferrable(self):
        constraint = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="unique_fields",
            deferrable=models.Deferrable.IMMEDIATE,
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: fields=('foo', 'bar') name='unique_fields' "
            "deferrable=Deferrable.IMMEDIATE>",
        )

    def test_repr_with_include(self):
        constraint = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="include_fields",
            include=["baz_1", "baz_2"],
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: fields=('foo', 'bar') name='include_fields' "
            "include=('baz_1', 'baz_2')>",
        )

    def test_repr_with_opclasses(self):
        constraint = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="opclasses_fields",
            opclasses=["text_pattern_ops", "varchar_pattern_ops"],
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: fields=('foo', 'bar') name='opclasses_fields' "
            "opclasses=['text_pattern_ops', 'varchar_pattern_ops']>",
        )

    def test_repr_with_nulls_distinct(self):
        constraint = models.UniqueConstraint(
            fields=["foo", "bar"],
            name="nulls_distinct_fields",
            nulls_distinct=False,
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: fields=('foo', 'bar') name='nulls_distinct_fields' "
            "nulls_distinct=False>",
        )

    def test_repr_with_expressions(self):
        constraint = models.UniqueConstraint(
            Lower("title"),
            F("author"),
            name="book_func_uq",
        )
        self.assertEqual(
            repr(constraint),
            "<UniqueConstraint: expressions=(Lower(F(title)), F(author)) "
            "name='book_func_uq'>",
        )

    def test_repr_with_violation_error_message(self):
        constraint = models.UniqueConstraint(
            models.F("baz__lower"),
            name="unique_lower_baz",
            violation_error_message="BAZ",
        )
        self.assertEqual(
            repr(constraint),
            (
                "<UniqueConstraint: expressions=(F(baz__lower),) "
                "name='unique_lower_baz' violation_error_message='BAZ'>"
            ),
        )

    def test_repr_with_violation_error_code(self):
        constraint = models.UniqueConstraint(
            models.F("baz__lower"),
            name="unique_lower_baz",
            violation_error_code="baz",
        )
        self.assertEqual(
            repr(constraint),
            (
                "<UniqueConstraint: expressions=(F(baz__lower),) "
                "name='unique_lower_baz' violation_error_code='baz'>"
            ),
        )

    def test_deconstruction(self):
        fields = ["foo", "bar"]
        name = "unique_fields"
        constraint = models.UniqueConstraint(fields=fields, name=name)
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {"fields": tuple(fields), "name": name})

    def test_deconstruction_with_condition(self):
        fields = ["foo", "bar"]
        name = "unique_fields"
        condition = models.Q(foo=models.F("bar"))
        constraint = models.UniqueConstraint(
            fields=fields, name=name, condition=condition
        )
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs, {"fields": tuple(fields), "name": name, "condition": condition}
        )

    def test_deconstruction_with_deferrable(self):
        fields = ["foo"]
        name = "unique_fields"
        constraint = models.UniqueConstraint(
            fields=fields,
            name=name,
            deferrable=models.Deferrable.DEFERRED,
        )
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs,
            {
                "fields": tuple(fields),
                "name": name,
                "deferrable": models.Deferrable.DEFERRED,
            },
        )

    def test_deconstruction_with_include(self):
        fields = ["foo", "bar"]
        name = "unique_fields"
        include = ["baz_1", "baz_2"]
        constraint = models.UniqueConstraint(fields=fields, name=name, include=include)
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs,
            {
                "fields": tuple(fields),
                "name": name,
                "include": tuple(include),
            },
        )

    def test_deconstruction_with_opclasses(self):
        fields = ["foo", "bar"]
        name = "unique_fields"
        opclasses = ["varchar_pattern_ops", "text_pattern_ops"]
        constraint = models.UniqueConstraint(
            fields=fields, name=name, opclasses=opclasses
        )
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs,
            {
                "fields": tuple(fields),
                "name": name,
                "opclasses": opclasses,
            },
        )

    def test_deconstruction_with_nulls_distinct(self):
        fields = ["foo", "bar"]
        name = "unique_fields"
        constraint = models.UniqueConstraint(
            fields=fields, name=name, nulls_distinct=True
        )
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, ())
        self.assertEqual(
            kwargs,
            {
                "fields": tuple(fields),
                "name": name,
                "nulls_distinct": True,
            },
        )

    def test_deconstruction_with_expressions(self):
        name = "unique_fields"
        constraint = models.UniqueConstraint(Lower("title"), name=name)
        path, args, kwargs = constraint.deconstruct()
        self.assertEqual(path, "django.db.models.UniqueConstraint")
        self.assertEqual(args, (Lower("title"),))
        self.assertEqual(kwargs, {"name": name})

    def test_database_constraint(self):
        with self.assertRaises(IntegrityError):
            UniqueConstraintProduct.objects.create(
                name=self.p1.name, color=self.p1.color
            )

    @skipUnlessDBFeature("supports_partial_indexes")
    def test_database_constraint_with_condition(self):
        UniqueConstraintConditionProduct.objects.create(name="p1")
        UniqueConstraintConditionProduct.objects.create(name="p2")
        with self.assertRaises(IntegrityError):
            UniqueConstraintConditionProduct.objects.create(name="p1")

    def test_model_validation(self):
        msg = "Unique constraint product with this Name and Color already exists."
        with self.assertRaisesMessage(ValidationError, msg):
            UniqueConstraintProduct(
                name=self.p1.name, color=self.p1.color
            ).validate_constraints()

    @skipUnlessDBFeature("supports_partial_indexes")
    def test_model_validation_with_condition(self):
        """
        Partial unique constraints are not ignored by
        Model.validate_constraints().
        """
        obj1 = UniqueConstraintConditionProduct.objects.create(name="p1", color="red")
        obj2 = UniqueConstraintConditionProduct.objects.create(name="p2")
        UniqueConstraintConditionProduct(
            name=obj1.name, color="blue"
        ).validate_constraints()
        msg = "Constraint “name_without_color_uniq” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            UniqueConstraintConditionProduct(name=obj2.name).validate_constraints()

    def test_model_validation_constraint_no_code_error(self):
        class ValidateNoCodeErrorConstraint(UniqueConstraint):
            def validate(self, model, instance, **kwargs):
                raise ValidationError({"name": ValidationError("Already exists.")})

        class NoCodeErrorConstraintModel(models.Model):
            name = models.CharField(max_length=255)

            class Meta:
                constraints = [
                    ValidateNoCodeErrorConstraint(
                        Lower("name"),
                        name="custom_validate_no_code_error",
                    )
                ]

        msg = "{'name': ['Already exists.']}"
        with self.assertRaisesMessage(ValidationError, msg):
            NoCodeErrorConstraintModel(name="test").validate_constraints()

    def test_validate(self):
        constraint = UniqueConstraintProduct._meta.constraints[0]
        msg = "Unique constraint product with this Name and Color already exists."
        non_unique_product = UniqueConstraintProduct(
            name=self.p1.name, color=self.p1.color
        )
        with self.assertRaisesMessage(ValidationError, msg) as cm:
            constraint.validate(UniqueConstraintProduct, non_unique_product)
        self.assertEqual(cm.exception.code, "unique_together")
        # Null values are ignored.
        constraint.validate(
            UniqueConstraintProduct,
            UniqueConstraintProduct(name=self.p2.name, color=None),
        )
        # Existing instances have their existing row excluded.
        constraint.validate(UniqueConstraintProduct, self.p1)
        # Unique fields are excluded.
        constraint.validate(
            UniqueConstraintProduct,
            non_unique_product,
            exclude={"name"},
        )
        constraint.validate(
            UniqueConstraintProduct,
            non_unique_product,
            exclude={"color"},
        )
        constraint.validate(
            UniqueConstraintProduct,
            non_unique_product,
            exclude={"name", "color"},
        )
        # Validation on a child instance.
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(
                UniqueConstraintProduct,
                ChildUniqueConstraintProduct(name=self.p1.name, color=self.p1.color),
            )

    def test_validate_unique_custom_code_and_message(self):
        product = UniqueConstraintProduct.objects.create(
            name="test", color="red", age=42
        )
        code = "custom_code"
        message = "Custom message"
        multiple_fields_constraint = models.UniqueConstraint(
            fields=["color", "age"],
            name="color_age_uniq",
            violation_error_code=code,
            violation_error_message=message,
        )
        single_field_constraint = models.UniqueConstraint(
            fields=["color"],
            name="color_uniq",
            violation_error_code=code,
            violation_error_message=message,
        )

        with self.assertRaisesMessage(ValidationError, message) as cm:
            multiple_fields_constraint.validate(
                UniqueConstraintProduct,
                UniqueConstraintProduct(
                    name="new-test", color=product.color, age=product.age
                ),
            )
        self.assertEqual(cm.exception.code, code)

        with self.assertRaisesMessage(ValidationError, message) as cm:
            single_field_constraint.validate(
                UniqueConstraintProduct,
                UniqueConstraintProduct(name="new-test", color=product.color),
            )
        self.assertEqual(cm.exception.code, code)

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_validate_fields_unattached(self):
        Product.objects.create(price=42)
        constraint = models.UniqueConstraint(fields=["price"], name="uniq_prices")
        msg = "Product with this Price already exists."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(Product, Product(price=42))

    @skipUnlessDBFeature("supports_partial_indexes")
    def test_validate_condition(self):
        p1 = UniqueConstraintConditionProduct.objects.create(name="p1")
        constraint = UniqueConstraintConditionProduct._meta.constraints[0]
        msg = "Constraint “name_without_color_uniq” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(
                UniqueConstraintConditionProduct,
                UniqueConstraintConditionProduct(name=p1.name, color=None),
            )
        # Values not matching condition are ignored.
        constraint.validate(
            UniqueConstraintConditionProduct,
            UniqueConstraintConditionProduct(name=p1.name, color="anything-but-none"),
        )
        # Existing instances have their existing row excluded.
        constraint.validate(UniqueConstraintConditionProduct, p1)
        # Unique field is excluded.
        constraint.validate(
            UniqueConstraintConditionProduct,
            UniqueConstraintConditionProduct(name=p1.name, color=None),
            exclude={"name"},
        )

    @skipUnlessDBFeature("supports_partial_indexes")
    def test_validate_condition_custom_error(self):
        p1 = UniqueConstraintConditionProduct.objects.create(name="p1")
        constraint = models.UniqueConstraint(
            fields=["name"],
            name="name_without_color_uniq",
            condition=models.Q(color__isnull=True),
            violation_error_code="custom_code",
            violation_error_message="Custom message",
        )
        msg = "Custom message"
        with self.assertRaisesMessage(ValidationError, msg) as cm:
            constraint.validate(
                UniqueConstraintConditionProduct,
                UniqueConstraintConditionProduct(name=p1.name, color=None),
            )
        self.assertEqual(cm.exception.code, "custom_code")

    def test_validate_expression(self):
        constraint = models.UniqueConstraint(Lower("name"), name="name_lower_uniq")
        msg = "Constraint “name_lower_uniq” 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_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"),
            name="name_lower_without_color_uniq",
            condition=models.Q(color__isnull=True),
        )
        non_unique_product = UniqueConstraintProduct(name=self.p2.name.upper())
        msg = "Constraint “name_lower_without_color_uniq” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(UniqueConstraintProduct, non_unique_product)
        # Values not matching condition are ignored.
        constraint.validate(
            UniqueConstraintProduct,
            UniqueConstraintProduct(name=self.p1.name, color=self.p1.color),
        )
        # Existing instances have their existing row excluded.
        constraint.validate(UniqueConstraintProduct, self.p2)
        # Unique field is excluded.
        constraint.validate(
            UniqueConstraintProduct,
            non_unique_product,
            exclude={"name"},
        )
        # Field from a condition is excluded.
        constraint.validate(
            UniqueConstraintProduct,
            non_unique_product,
            exclude={"color"},
        )

    def test_validate_expression_str(self):
        constraint = models.UniqueConstraint("name", name="name_uniq")
        msg = "Constraint “name_uniq” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(
                UniqueConstraintProduct,
                UniqueConstraintProduct(name=self.p1.name),
            )
        constraint.validate(
            UniqueConstraintProduct,
            UniqueConstraintProduct(name=self.p1.name),
            exclude={"name"},
        )

    @skipUnlessDBFeature("supports_stored_generated_columns")
    def test_validate_expression_generated_field_stored(self):
        self.assertGeneratedFieldWithExpressionIsValidated(
            model=GeneratedFieldStoredProduct
        )

    @skipUnlessDBFeature("supports_virtual_generated_columns")
    def test_validate_expression_generated_field_virtual(self):
        self.assertGeneratedFieldWithExpressionIsValidated(
            model=GeneratedFieldVirtualProduct
        )

    def assertGeneratedFieldWithExpressionIsValidated(self, model):
        constraint = UniqueConstraint(Sqrt("rebate"), name="unique_rebate_sqrt")
        model.objects.create(price=100, discounted_price=84)

        valid_product = model(price=100, discounted_price=75)
        constraint.validate(model, valid_product)

        invalid_product = model(price=20, discounted_price=4)
        with self.assertRaisesMessage(
            ValidationError, f"Constraint “{constraint.name}” is violated."
        ):
            constraint.validate(model, invalid_product)

        # Excluding referenced or generated fields should skip validation.
        constraint.validate(model, invalid_product, exclude={"rebate"})
        constraint.validate(model, invalid_product, exclude={"price"})

    @skipUnlessDBFeature("supports_stored_generated_columns")
    def test_validate_fields_generated_field_stored(self):
        self.assertGeneratedFieldWithFieldsIsValidated(
            model=GeneratedFieldStoredProduct
        )

    @skipUnlessDBFeature("supports_virtual_generated_columns")
    def test_validate_fields_generated_field_virtual(self):
        self.assertGeneratedFieldWithFieldsIsValidated(
            model=GeneratedFieldVirtualProduct
        )

    def assertGeneratedFieldWithFieldsIsValidated(self, model):
        constraint = models.UniqueConstraint(
            fields=["lower_name"], name="lower_name_unique"
        )
        model.objects.create(name="Box")
        constraint.validate(model, model(name="Case"))

        invalid_product = model(name="BOX")
        msg = str(invalid_product.unique_error_message(model, ["lower_name"]))
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(model, invalid_product)

        # Excluding referenced or generated fields should skip validation.
        constraint.validate(model, invalid_product, exclude={"lower_name"})
        constraint.validate(model, invalid_product, exclude={"name"})

    @skipUnlessDBFeature("supports_stored_generated_columns")
    def test_validate_fields_generated_field_stored_nulls_distinct(self):
        self.assertGeneratedFieldNullsDistinctIsValidated(
            model=GeneratedFieldStoredProduct
        )

    @skipUnlessDBFeature("supports_virtual_generated_columns")
    def test_validate_fields_generated_field_virtual_nulls_distinct(self):
        self.assertGeneratedFieldNullsDistinctIsValidated(
            model=GeneratedFieldVirtualProduct
        )

    def assertGeneratedFieldNullsDistinctIsValidated(self, model):
        constraint = models.UniqueConstraint(
            fields=["lower_name"],
            name="lower_name_unique_nulls_distinct",
            nulls_distinct=False,
        )
        model.objects.create(name=None)
        valid_product = model(name="Box")
        constraint.validate(model, valid_product)

        invalid_product = model(name=None)
        msg = str(invalid_product.unique_error_message(model, ["lower_name"]))
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(model, invalid_product)

    @skipUnlessDBFeature("supports_table_check_constraints")
    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))

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_validate_nulls_distinct_fields(self):
        Product.objects.create(price=42)
        constraint = models.UniqueConstraint(
            fields=["price"],
            nulls_distinct=False,
            name="uniq_prices_nulls_distinct",
        )
        constraint.validate(Product, Product(price=None))
        Product.objects.create(price=None)
        msg = "Product with this Price already exists."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(Product, Product(price=None))

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_validate_nulls_distinct_expressions(self):
        Product.objects.create(price=42)
        constraint = models.UniqueConstraint(
            Abs("price"),
            nulls_distinct=False,
            name="uniq_prices_nulls_distinct",
        )
        constraint.validate(Product, Product(price=None))
        Product.objects.create(price=None)
        msg = f"Constraint “{constraint.name}” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            constraint.validate(Product, Product(price=None))

    def test_name(self):
        constraints = get_constraints(UniqueConstraintProduct._meta.db_table)
        expected_name = "name_color_uniq"
        self.assertIn(expected_name, constraints)

    def test_condition_must_be_q(self):
        with self.assertRaisesMessage(
            ValueError, "UniqueConstraint.condition must be a Q instance."
        ):
            models.UniqueConstraint(name="uniq", fields=["name"], condition="invalid")

    @skipUnlessDBFeature("supports_deferrable_unique_constraints")
    def test_initially_deferred_database_constraint(self):
        obj_1 = UniqueConstraintDeferrable.objects.create(name="p1", shelf="front")
        obj_2 = UniqueConstraintDeferrable.objects.create(name="p2", shelf="back")

        def swap():
            obj_1.name, obj_2.name = obj_2.name, obj_1.name
            obj_1.save()
            obj_2.save()

        swap()
        # Behavior can be changed with SET CONSTRAINTS.
        with self.assertRaises(IntegrityError):
            with atomic(), connection.cursor() as cursor:
                constraint_name = connection.ops.quote_name("name_init_deferred_uniq")
                cursor.execute("SET CONSTRAINTS %s IMMEDIATE" % constraint_name)
                swap()

    @skipUnlessDBFeature("supports_deferrable_unique_constraints")
    def test_initially_immediate_database_constraint(self):
        obj_1 = UniqueConstraintDeferrable.objects.create(name="p1", shelf="front")
        obj_2 = UniqueConstraintDeferrable.objects.create(name="p2", shelf="back")
        obj_1.shelf, obj_2.shelf = obj_2.shelf, obj_1.shelf
        with self.assertRaises(IntegrityError), atomic():
            obj_1.save()
        # Behavior can be changed with SET CONSTRAINTS.
        with connection.cursor() as cursor:
            constraint_name = connection.ops.quote_name("sheld_init_immediate_uniq")
            cursor.execute("SET CONSTRAINTS %s DEFERRED" % constraint_name)
            obj_1.save()
            obj_2.save()

    def test_deferrable_with_condition(self):
        message = "UniqueConstraint with conditions cannot be deferred."
        with self.assertRaisesMessage(ValueError, message):
            models.UniqueConstraint(
                fields=["name"],
                name="name_without_color_unique",
                condition=models.Q(color__isnull=True),
                deferrable=models.Deferrable.DEFERRED,
            )

    def test_deferrable_with_include(self):
        message = "UniqueConstraint with include fields cannot be deferred."
        with self.assertRaisesMessage(ValueError, message):
            models.UniqueConstraint(
                fields=["name"],
                name="name_inc_color_color_unique",
                include=["color"],
                deferrable=models.Deferrable.DEFERRED,
            )

    def test_deferrable_with_opclasses(self):
        message = "UniqueConstraint with opclasses cannot be deferred."
        with self.assertRaisesMessage(ValueError, message):
            models.UniqueConstraint(
                fields=["name"],
                name="name_text_pattern_ops_unique",
                opclasses=["text_pattern_ops"],
                deferrable=models.Deferrable.DEFERRED,
            )

    def test_deferrable_with_expressions(self):
        message = "UniqueConstraint with expressions cannot be deferred."
        with self.assertRaisesMessage(ValueError, message):
            models.UniqueConstraint(
                Lower("name"),
                name="deferred_expression_unique",
                deferrable=models.Deferrable.DEFERRED,
            )

    def test_invalid_defer_argument(self):
        message = "UniqueConstraint.deferrable must be a Deferrable instance."
        with self.assertRaisesMessage(TypeError, message):
            models.UniqueConstraint(
                fields=["name"],
                name="name_invalid",
                deferrable="invalid",
            )

    @skipUnlessDBFeature(
        "supports_table_check_constraints",
        "supports_covering_indexes",
    )
    def test_include_database_constraint(self):
        UniqueConstraintInclude.objects.create(name="p1", color="red")
        with self.assertRaises(IntegrityError):
            UniqueConstraintInclude.objects.create(name="p1", color="blue")

    def test_invalid_include_argument(self):
        msg = "UniqueConstraint.include must be a list or tuple."
        with self.assertRaisesMessage(TypeError, msg):
            models.UniqueConstraint(
                name="uniq_include",
                fields=["field"],
                include="other",
            )

    def test_invalid_opclasses_argument(self):
        msg = "UniqueConstraint.opclasses must be a list or tuple."
        with self.assertRaisesMessage(TypeError, msg):
            models.UniqueConstraint(
                name="uniq_opclasses",
                fields=["field"],
                opclasses="jsonb_path_ops",
            )

    def test_invalid_nulls_distinct_argument(self):
        msg = "UniqueConstraint.nulls_distinct must be a bool."
        with self.assertRaisesMessage(TypeError, msg):
            models.UniqueConstraint(
                name="uniq_opclasses", fields=["field"], nulls_distinct="NULLS DISTINCT"
            )

    def test_opclasses_and_fields_same_length(self):
        msg = (
            "UniqueConstraint.fields and UniqueConstraint.opclasses must have "
            "the same number of elements."
        )
        with self.assertRaisesMessage(ValueError, msg):
            models.UniqueConstraint(
                name="uniq_opclasses",
                fields=["field"],
                opclasses=["foo", "bar"],
            )

    def test_requires_field_or_expression(self):
        msg = (
            "At least one field or expression is required to define a unique "
            "constraint."
        )
        with self.assertRaisesMessage(ValueError, msg):
            models.UniqueConstraint(name="name")

    def test_expressions_and_fields_mutually_exclusive(self):
        msg = "UniqueConstraint.fields and expressions are mutually exclusive."
        with self.assertRaisesMessage(ValueError, msg):
            models.UniqueConstraint(Lower("field_1"), fields=["field_2"], name="name")

    def test_expressions_with_opclasses(self):
        msg = (
            "UniqueConstraint.opclasses cannot be used with expressions. Use "
            "django.contrib.postgres.indexes.OpClass() instead."
        )
        with self.assertRaisesMessage(ValueError, msg):
            models.UniqueConstraint(
                Lower("field"),
                name="test_func_opclass",
                opclasses=["jsonb_path_ops"],
            )

    def test_requires_name(self):
        msg = "A unique constraint must be named."
        with self.assertRaisesMessage(ValueError, msg):
            models.UniqueConstraint(fields=["field"])

    def test_database_default(self):
        models.UniqueConstraint(
            fields=["field_with_db_default"], name="unique_field_with_db_default"
        ).validate(ModelWithDatabaseDefault, ModelWithDatabaseDefault())
        models.UniqueConstraint(
            Upper("field_with_db_default"),
            name="unique_field_with_db_default_expression",
        ).validate(ModelWithDatabaseDefault, ModelWithDatabaseDefault())

        ModelWithDatabaseDefault.objects.create()

        msg = (
            "Model with database default with this Field with db default already "
            "exists."
        )
        with self.assertRaisesMessage(ValidationError, msg):
            models.UniqueConstraint(
                fields=["field_with_db_default"], name="unique_field_with_db_default"
            ).validate(ModelWithDatabaseDefault, ModelWithDatabaseDefault())

        msg = "Constraint “unique_field_with_db_default_expression” is violated."
        with self.assertRaisesMessage(ValidationError, msg):
            models.UniqueConstraint(
                Upper("field_with_db_default"),
                name="unique_field_with_db_default_expression",
            ).validate(ModelWithDatabaseDefault, ModelWithDatabaseDefault())