import unittest

from django.core.checks import Error, Warning
from django.core.checks.model_checks import _check_lazy_references
from django.db import connection, connections, models
from django.db.models.functions import Abs, Lower, Round
from django.db.models.signals import post_init
from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
from django.test.utils import isolate_apps, override_settings, register_lookup


class EmptyRouter:
    pass


def get_max_column_name_length():
    allowed_len = None
    db_alias = None

    for db in ("default", "other"):
        connection = connections[db]
        max_name_length = connection.ops.max_name_length()
        if max_name_length is not None and not connection.features.truncates_names:
            if allowed_len is None or max_name_length < allowed_len:
                allowed_len = max_name_length
                db_alias = db

    return (allowed_len, db_alias)


@isolate_apps("invalid_models_tests")
class UniqueTogetherTests(SimpleTestCase):
    def test_non_iterable(self):
        class Model(models.Model):
            class Meta:
                unique_together = 42

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'unique_together' must be a list or tuple.",
                    obj=Model,
                    id="models.E010",
                ),
            ],
        )

    def test_list_containing_non_iterable(self):
        class Model(models.Model):
            one = models.IntegerField()
            two = models.IntegerField()

            class Meta:
                unique_together = [("a", "b"), 42]

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "All 'unique_together' elements must be lists or tuples.",
                    obj=Model,
                    id="models.E011",
                ),
            ],
        )

    def test_non_list(self):
        class Model(models.Model):
            class Meta:
                unique_together = "not-a-list"

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'unique_together' must be a list or tuple.",
                    obj=Model,
                    id="models.E010",
                ),
            ],
        )

    def test_valid_model(self):
        class Model(models.Model):
            one = models.IntegerField()
            two = models.IntegerField()

            class Meta:
                # unique_together can be a simple tuple
                unique_together = ("one", "two")

        self.assertEqual(Model.check(), [])

    def test_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                unique_together = [["missing_field"]]

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'unique_together' refers to the nonexistent field "
                    "'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    def test_pointing_to_m2m(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                unique_together = [["m2m"]]

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'unique_together' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'unique_together'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    def test_pointing_to_fk(self):
        class Foo(models.Model):
            pass

        class Bar(models.Model):
            foo_1 = models.ForeignKey(
                Foo, on_delete=models.CASCADE, related_name="bar_1"
            )
            foo_2 = models.ForeignKey(
                Foo, on_delete=models.CASCADE, related_name="bar_2"
            )

            class Meta:
                unique_together = [["foo_1_id", "foo_2"]]

        self.assertEqual(Bar.check(), [])

    def test_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                unique_together = [["pk"]]

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'unique_together' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'unique_together'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_pointing_to_foreign_object(self):
        class Reference(models.Model):
            reference_id = models.IntegerField(unique=True)

        class ReferenceTab(models.Model):
            reference_id = models.IntegerField()
            reference = models.ForeignObject(
                Reference,
                from_fields=["reference_id"],
                to_fields=["reference_id"],
                on_delete=models.CASCADE,
            )

            class Meta:
                unique_together = [["reference"]]

        self.assertEqual(ReferenceTab.check(), [])

    def test_pointing_to_foreign_object_multi_column(self):
        class Reference(models.Model):
            reference_id = models.IntegerField(unique=True)
            code = models.CharField(max_length=1)

        class ReferenceTabMultiple(models.Model):
            reference_id = models.IntegerField()
            code = models.CharField(max_length=1)
            reference = models.ForeignObject(
                Reference,
                from_fields=["reference_id", "code"],
                to_fields=["reference_id", "code"],
                on_delete=models.CASCADE,
            )

            class Meta:
                unique_together = [["reference"]]

        self.assertEqual(
            ReferenceTabMultiple.check(),
            [
                Error(
                    "'unique_together' refers to a ForeignObject 'reference' with "
                    "multiple 'from_fields', which is not supported for that option.",
                    obj=ReferenceTabMultiple,
                    id="models.E049",
                ),
            ],
        )


@isolate_apps("invalid_models_tests")
class IndexesTests(TestCase):
    def test_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                indexes = [models.Index(fields=["missing_field"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    def test_pointing_to_desc_field(self):
        class Model(models.Model):
            name = models.CharField(max_length=100)

            class Meta:
                indexes = [models.Index(fields=["-name"], name="index_name")]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                indexes = [models.Index(fields=["m2m"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    def test_pointing_to_non_local_field(self):
        class Foo(models.Model):
            field1 = models.IntegerField()

        class Bar(Foo):
            field2 = models.IntegerField()

            class Meta:
                indexes = [models.Index(fields=["field2", "field1"], name="name")]

        self.assertEqual(
            Bar.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to field 'field1' which is not local to "
                    "model 'Bar'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Bar,
                    id="models.E016",
                ),
            ],
        )

    def test_pointing_to_fk(self):
        class Foo(models.Model):
            pass

        class Bar(models.Model):
            foo_1 = models.ForeignKey(
                Foo, on_delete=models.CASCADE, related_name="bar_1"
            )
            foo_2 = models.ForeignKey(
                Foo, on_delete=models.CASCADE, related_name="bar_2"
            )

            class Meta:
                indexes = [
                    models.Index(fields=["foo_1_id", "foo_2"], name="index_name")
                ]

        self.assertEqual(Bar.check(databases=self.databases), [])

    def test_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                indexes = [models.Index(fields=["pk", "name"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_name_constraints(self):
        class Model(models.Model):
            class Meta:
                indexes = [
                    models.Index(fields=["id"], name="_index_name"),
                    models.Index(fields=["id"], name="5index_name"),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "The index name '%sindex_name' cannot start with an "
                    "underscore or a number." % prefix,
                    obj=Model,
                    id="models.E033",
                )
                for prefix in ("_", "5")
            ],
        )

    def test_max_name_length(self):
        index_name = "x" * 31

        class Model(models.Model):
            class Meta:
                indexes = [models.Index(fields=["id"], name=index_name)]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "The index name '%s' cannot be longer than 30 characters."
                    % index_name,
                    obj=Model,
                    id="models.E034",
                ),
            ],
        )

    def test_index_with_condition(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                indexes = [
                    models.Index(
                        fields=["age"],
                        name="index_age_gte_10",
                        condition=models.Q(age__gte=10),
                    ),
                ]

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_partial_indexes
            else [
                Warning(
                    "%s does not support indexes with conditions."
                    % connection.display_name,
                    hint=(
                        "Conditions will be ignored. Silence this warning if you "
                        "don't care about it."
                    ),
                    obj=Model,
                    id="models.W037",
                )
            ]
        )
        self.assertEqual(errors, expected)

    def test_index_with_condition_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_partial_indexes"}
                indexes = [
                    models.Index(
                        fields=["age"],
                        name="index_age_gte_10",
                        condition=models.Q(age__gte=10),
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_index_with_include(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                indexes = [
                    models.Index(
                        fields=["age"],
                        name="index_age_include_id",
                        include=["id"],
                    ),
                ]

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_covering_indexes
            else [
                Warning(
                    "%s does not support indexes with non-key columns."
                    % connection.display_name,
                    hint=(
                        "Non-key columns will be ignored. Silence this warning if "
                        "you don't care about it."
                    ),
                    obj=Model,
                    id="models.W040",
                )
            ]
        )
        self.assertEqual(errors, expected)

    def test_index_with_include_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_covering_indexes"}
                indexes = [
                    models.Index(
                        fields=["age"],
                        name="index_age_include_id",
                        include=["id"],
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_index_include_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                indexes = [
                    models.Index(fields=["id"], include=["missing_field"], name="name"),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_index_include_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                indexes = [models.Index(fields=["id"], include=["m2m"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_index_include_pointing_to_non_local_field(self):
        class Parent(models.Model):
            field1 = models.IntegerField()

        class Child(Parent):
            field2 = models.IntegerField()

            class Meta:
                indexes = [
                    models.Index(fields=["field2"], include=["field1"], name="name"),
                ]

        self.assertEqual(
            Child.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to field 'field1' which is not local to "
                    "model 'Child'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Child,
                    id="models.E016",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_index_include_pointing_to_fk(self):
        class Target(models.Model):
            pass

        class Model(models.Model):
            fk_1 = models.ForeignKey(Target, models.CASCADE, related_name="target_1")
            fk_2 = models.ForeignKey(Target, models.CASCADE, related_name="target_2")

            class Meta:
                indexes = [
                    models.Index(
                        fields=["id"],
                        include=["fk_1_id", "fk_2"],
                        name="name",
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_index_include_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                indexes = [models.Index(fields=["name"], include=["pk"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_func_index(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                indexes = [models.Index(Lower("name"), name="index_lower_name")]

        warn = Warning(
            "%s does not support indexes on expressions." % connection.display_name,
            hint=(
                "An index won't be created. Silence this warning if you don't "
                "care about it."
            ),
            obj=Model,
            id="models.W043",
        )
        expected = [] if connection.features.supports_expression_indexes else [warn]
        self.assertEqual(Model.check(databases=self.databases), expected)

    def test_func_index_required_db_features(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                indexes = [models.Index(Lower("name"), name="index_lower_name")]
                required_db_features = {"supports_expression_indexes"}

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_complex_expression_custom_lookup(self):
        class Model(models.Model):
            height = models.IntegerField()
            weight = models.IntegerField()

            class Meta:
                indexes = [
                    models.Index(
                        models.F("height")
                        / (models.F("weight__abs") + models.Value(5)),
                        name="name",
                    ),
                ]

        with register_lookup(models.IntegerField, Abs):
            self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                indexes = [models.Index(Lower("missing_field").desc(), name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_missing_field_nested(self):
        class Model(models.Model):
            class Meta:
                indexes = [
                    models.Index(Abs(Round("missing_field")), name="name"),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                indexes = [models.Index(Lower("m2m"), name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_non_local_field(self):
        class Foo(models.Model):
            field1 = models.CharField(max_length=15)

        class Bar(Foo):
            class Meta:
                indexes = [models.Index(Lower("field1"), name="name")]

        self.assertEqual(
            Bar.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to field 'field1' which is not local to "
                    "model 'Bar'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Bar,
                    id="models.E016",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_fk(self):
        class Foo(models.Model):
            pass

        class Bar(models.Model):
            foo_1 = models.ForeignKey(Foo, models.CASCADE, related_name="bar_1")
            foo_2 = models.ForeignKey(Foo, models.CASCADE, related_name="bar_2")

            class Meta:
                indexes = [
                    models.Index(Lower("foo_1_id"), Lower("foo_2"), name="index_name"),
                ]

        self.assertEqual(Bar.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_index_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                indexes = [models.Index(Abs("pk"), name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'indexes' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'indexes'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )


@isolate_apps("invalid_models_tests")
class FieldNamesTests(TestCase):
    databases = {"default", "other"}

    def test_ending_with_underscore(self):
        class Model(models.Model):
            field_ = models.CharField(max_length=10)
            m2m_ = models.ManyToManyField("self")

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "Field names must not end with an underscore.",
                    obj=Model._meta.get_field("field_"),
                    id="fields.E001",
                ),
                Error(
                    "Field names must not end with an underscore.",
                    obj=Model._meta.get_field("m2m_"),
                    id="fields.E001",
                ),
            ],
        )

    max_column_name_length, column_limit_db_alias = get_max_column_name_length()

    @unittest.skipIf(
        max_column_name_length is None,
        "The database doesn't have a column name length limit.",
    )
    def test_M2M_long_column_name(self):
        """
        #13711 -- Model check for long M2M column names when database has
        column name length limits.
        """

        # A model with very long name which will be used to set relations to.
        class VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz(
            models.Model
        ):
            title = models.CharField(max_length=11)

        # Main model for which checks will be performed.
        class ModelWithLongField(models.Model):
            m2m_field = models.ManyToManyField(
                VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
                related_name="rn1",
            )
            m2m_field2 = models.ManyToManyField(
                VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
                related_name="rn2",
                through="m2msimple",
            )
            m2m_field3 = models.ManyToManyField(
                VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
                related_name="rn3",
                through="m2mcomplex",
            )
            fk = models.ForeignKey(
                VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
                models.CASCADE,
                related_name="rn4",
            )

        # Models used for setting `through` in M2M field.
        class m2msimple(models.Model):
            id2 = models.ForeignKey(ModelWithLongField, models.CASCADE)

        class m2mcomplex(models.Model):
            id2 = models.ForeignKey(ModelWithLongField, models.CASCADE)

        long_field_name = "a" * (self.max_column_name_length + 1)
        models.ForeignKey(
            VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
            models.CASCADE,
        ).contribute_to_class(m2msimple, long_field_name)

        models.ForeignKey(
            VeryLongModelNamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,
            models.CASCADE,
            db_column=long_field_name,
        ).contribute_to_class(m2mcomplex, long_field_name)

        errors = ModelWithLongField.check(databases=("default", "other"))

        # First error because of M2M field set on the model with long name.
        m2m_long_name = (
            "verylongmodelnamezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz_id"
        )
        if self.max_column_name_length > len(m2m_long_name):
            # Some databases support names longer than the test name.
            expected = []
        else:
            expected = [
                Error(
                    'Autogenerated column name too long for M2M field "%s". '
                    'Maximum length is "%s" for database "%s".'
                    % (
                        m2m_long_name,
                        self.max_column_name_length,
                        self.column_limit_db_alias,
                    ),
                    hint="Use 'through' to create a separate model for "
                    "M2M and then set column_name using 'db_column'.",
                    obj=ModelWithLongField,
                    id="models.E019",
                )
            ]

        # Second error because the FK specified in the `through` model
        # `m2msimple` has auto-generated name longer than allowed.
        # There will be no check errors in the other M2M because it
        # specifies db_column for the FK in `through` model even if the actual
        # name is longer than the limits of the database.
        expected.append(
            Error(
                'Autogenerated column name too long for M2M field "%s_id". '
                'Maximum length is "%s" for database "%s".'
                % (
                    long_field_name,
                    self.max_column_name_length,
                    self.column_limit_db_alias,
                ),
                hint="Use 'through' to create a separate model for "
                "M2M and then set column_name using 'db_column'.",
                obj=ModelWithLongField,
                id="models.E019",
            )
        )

        self.assertEqual(errors, expected)
        # Check for long column names is called only for specified database
        # aliases.
        self.assertEqual(ModelWithLongField.check(databases=None), [])

    @unittest.skipIf(
        max_column_name_length is None,
        "The database doesn't have a column name length limit.",
    )
    def test_local_field_long_column_name(self):
        """
        #13711 -- Model check for long column names
        when database does not support long names.
        """

        class ModelWithLongField(models.Model):
            title = models.CharField(max_length=11)

        long_field_name = "a" * (self.max_column_name_length + 1)
        long_field_name2 = "b" * (self.max_column_name_length + 1)
        models.CharField(max_length=11).contribute_to_class(
            ModelWithLongField, long_field_name
        )
        models.CharField(max_length=11, db_column="vlmn").contribute_to_class(
            ModelWithLongField, long_field_name2
        )
        self.assertEqual(
            ModelWithLongField.check(databases=("default", "other")),
            [
                Error(
                    'Autogenerated column name too long for field "%s". '
                    'Maximum length is "%s" for database "%s".'
                    % (
                        long_field_name,
                        self.max_column_name_length,
                        self.column_limit_db_alias,
                    ),
                    hint="Set the column name manually using 'db_column'.",
                    obj=ModelWithLongField,
                    id="models.E018",
                )
            ],
        )
        # Check for long column names is called only for specified database
        # aliases.
        self.assertEqual(ModelWithLongField.check(databases=None), [])

    def test_including_separator(self):
        class Model(models.Model):
            some__field = models.IntegerField()

        self.assertEqual(
            Model.check(),
            [
                Error(
                    'Field names must not contain "__".',
                    obj=Model._meta.get_field("some__field"),
                    id="fields.E002",
                )
            ],
        )

    def test_pk(self):
        class Model(models.Model):
            pk = models.IntegerField()

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'pk' is a reserved word that cannot be used as a field name.",
                    obj=Model._meta.get_field("pk"),
                    id="fields.E003",
                )
            ],
        )

    def test_db_column_clash(self):
        class Model(models.Model):
            foo = models.IntegerField()
            bar = models.IntegerField(db_column="foo")

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "Field 'bar' has column name 'foo' that is used by "
                    "another field.",
                    hint="Specify a 'db_column' for the field.",
                    obj=Model,
                    id="models.E007",
                )
            ],
        )


@isolate_apps("invalid_models_tests")
class ShadowingFieldsTests(SimpleTestCase):
    def test_field_name_clash_with_child_accessor(self):
        class Parent(models.Model):
            pass

        class Child(Parent):
            child = models.CharField(max_length=100)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "The field 'child' clashes with the field "
                    "'child' from model 'invalid_models_tests.parent'.",
                    obj=Child._meta.get_field("child"),
                    id="models.E006",
                )
            ],
        )

    def test_field_name_clash_with_m2m_through(self):
        class Parent(models.Model):
            clash_id = models.IntegerField()

        class Child(Parent):
            clash = models.ForeignKey("Child", models.CASCADE)

        class Model(models.Model):
            parents = models.ManyToManyField(
                to=Parent,
                through="Through",
                through_fields=["parent", "model"],
            )

        class Through(models.Model):
            parent = models.ForeignKey(Parent, models.CASCADE)
            model = models.ForeignKey(Model, models.CASCADE)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "The field 'clash' clashes with the field 'clash_id' from "
                    "model 'invalid_models_tests.parent'.",
                    obj=Child._meta.get_field("clash"),
                    id="models.E006",
                )
            ],
        )

    def test_multiinheritance_clash(self):
        class Mother(models.Model):
            clash = models.IntegerField()

        class Father(models.Model):
            clash = models.IntegerField()

        class Child(Mother, Father):
            # Here we have two clashed: id (automatic field) and clash, because
            # both parents define these fields.
            pass

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "The field 'id' from parent model "
                    "'invalid_models_tests.mother' clashes with the field 'id' "
                    "from parent model 'invalid_models_tests.father'.",
                    obj=Child,
                    id="models.E005",
                ),
                Error(
                    "The field 'clash' from parent model "
                    "'invalid_models_tests.mother' clashes with the field 'clash' "
                    "from parent model 'invalid_models_tests.father'.",
                    obj=Child,
                    id="models.E005",
                ),
            ],
        )

    def test_inheritance_clash(self):
        class Parent(models.Model):
            f_id = models.IntegerField()

        class Target(models.Model):
            # This field doesn't result in a clash.
            f_id = models.IntegerField()

        class Child(Parent):
            # This field clashes with parent "f_id" field.
            f = models.ForeignKey(Target, models.CASCADE)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "The field 'f' clashes with the field 'f_id' "
                    "from model 'invalid_models_tests.parent'.",
                    obj=Child._meta.get_field("f"),
                    id="models.E006",
                )
            ],
        )

    def test_multigeneration_inheritance(self):
        class GrandParent(models.Model):
            clash = models.IntegerField()

        class Parent(GrandParent):
            pass

        class Child(Parent):
            pass

        class GrandChild(Child):
            clash = models.IntegerField()

        self.assertEqual(
            GrandChild.check(),
            [
                Error(
                    "The field 'clash' clashes with the field 'clash' "
                    "from model 'invalid_models_tests.grandparent'.",
                    obj=GrandChild._meta.get_field("clash"),
                    id="models.E006",
                )
            ],
        )

    def test_diamond_mti_common_parent(self):
        class GrandParent(models.Model):
            pass

        class Parent(GrandParent):
            pass

        class Child(Parent):
            pass

        class MTICommonParentModel(Child, GrandParent):
            pass

        self.assertEqual(
            MTICommonParentModel.check(),
            [
                Error(
                    "The field 'grandparent_ptr' clashes with the field "
                    "'grandparent_ptr' from model 'invalid_models_tests.parent'.",
                    obj=MTICommonParentModel,
                    id="models.E006",
                )
            ],
        )

    def test_id_clash(self):
        class Target(models.Model):
            pass

        class Model(models.Model):
            fk = models.ForeignKey(Target, models.CASCADE)
            fk_id = models.IntegerField()

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "The field 'fk_id' clashes with the field 'fk' from model "
                    "'invalid_models_tests.model'.",
                    obj=Model._meta.get_field("fk_id"),
                    id="models.E006",
                )
            ],
        )


@isolate_apps("invalid_models_tests")
class OtherModelTests(SimpleTestCase):
    def test_unique_primary_key(self):
        invalid_id = models.IntegerField(primary_key=False)

        class Model(models.Model):
            id = invalid_id

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'id' can only be used as a field name if the field also sets "
                    "'primary_key=True'.",
                    obj=Model,
                    id="models.E004",
                ),
            ],
        )

    def test_ordering_non_iterable(self):
        class Model(models.Model):
            class Meta:
                ordering = "missing_field"

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'ordering' must be a tuple or list "
                    "(even if you want to order by only one field).",
                    obj=Model,
                    id="models.E014",
                ),
            ],
        )

    def test_just_ordering_no_errors(self):
        class Model(models.Model):
            order = models.PositiveIntegerField()

            class Meta:
                ordering = ["order"]

        self.assertEqual(Model.check(), [])

    def test_just_order_with_respect_to_no_errors(self):
        class Question(models.Model):
            pass

        class Answer(models.Model):
            question = models.ForeignKey(Question, models.CASCADE)

            class Meta:
                order_with_respect_to = "question"

        self.assertEqual(Answer.check(), [])

    def test_ordering_with_order_with_respect_to(self):
        class Question(models.Model):
            pass

        class Answer(models.Model):
            question = models.ForeignKey(Question, models.CASCADE)
            order = models.IntegerField()

            class Meta:
                order_with_respect_to = "question"
                ordering = ["order"]

        self.assertEqual(
            Answer.check(),
            [
                Error(
                    "'ordering' and 'order_with_respect_to' cannot be used together.",
                    obj=Answer,
                    id="models.E021",
                ),
            ],
        )

    def test_non_valid(self):
        class RelationModel(models.Model):
            pass

        class Model(models.Model):
            relation = models.ManyToManyField(RelationModel)

            class Meta:
                ordering = ["relation"]

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'relation'.",
                    obj=Model,
                    id="models.E015",
                ),
            ],
        )

    def test_ordering_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                ordering = ("missing_field",)

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'missing_field'.",
                    obj=Model,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_to_missing_foreignkey_field(self):
        class Model(models.Model):
            missing_fk_field = models.IntegerField()

            class Meta:
                ordering = ("missing_fk_field_id",)

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'missing_fk_field_id'.",
                    obj=Model,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_to_missing_related_field(self):
        class Model(models.Model):
            test = models.IntegerField()

            class Meta:
                ordering = ("missing_related__id",)

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'missing_related__id'.",
                    obj=Model,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_to_missing_related_model_field(self):
        class Parent(models.Model):
            pass

        class Child(models.Model):
            parent = models.ForeignKey(Parent, models.CASCADE)

            class Meta:
                ordering = ("parent__missing_field",)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'parent__missing_field'.",
                    obj=Child,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_to_non_related_field(self):
        class Child(models.Model):
            parent = models.IntegerField()

            class Meta:
                ordering = ("parent__missing_field",)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'parent__missing_field'.",
                    obj=Child,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_to_two_related_model_field(self):
        class Parent2(models.Model):
            pass

        class Parent1(models.Model):
            parent2 = models.ForeignKey(Parent2, models.CASCADE)

        class Child(models.Model):
            parent1 = models.ForeignKey(Parent1, models.CASCADE)

            class Meta:
                ordering = ("parent1__parent2__missing_field",)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'parent1__parent2__missing_field'.",
                    obj=Child,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_pointing_multiple_times_to_model_fields(self):
        class Parent(models.Model):
            field1 = models.CharField(max_length=100)
            field2 = models.CharField(max_length=100)

        class Child(models.Model):
            parent = models.ForeignKey(Parent, models.CASCADE)

            class Meta:
                ordering = ("parent__field1__field2",)

        self.assertEqual(
            Child.check(),
            [
                Error(
                    "'ordering' refers to the nonexistent field, related field, "
                    "or lookup 'parent__field1__field2'.",
                    obj=Child,
                    id="models.E015",
                )
            ],
        )

    def test_ordering_allows_registered_lookups(self):
        class Model(models.Model):
            test = models.CharField(max_length=100)

            class Meta:
                ordering = ("test__lower",)

        with register_lookup(models.CharField, Lower):
            self.assertEqual(Model.check(), [])

    def test_ordering_pointing_to_lookup_not_transform(self):
        class Model(models.Model):
            test = models.CharField(max_length=100)

            class Meta:
                ordering = ("test__isnull",)

        self.assertEqual(Model.check(), [])

    def test_ordering_pointing_to_related_model_pk(self):
        class Parent(models.Model):
            pass

        class Child(models.Model):
            parent = models.ForeignKey(Parent, models.CASCADE)

            class Meta:
                ordering = ("parent__pk",)

        self.assertEqual(Child.check(), [])

    def test_ordering_pointing_to_foreignkey_field(self):
        class Parent(models.Model):
            pass

        class Child(models.Model):
            parent = models.ForeignKey(Parent, models.CASCADE)

            class Meta:
                ordering = ("parent_id",)

        self.assertFalse(Child.check())

    def test_name_beginning_with_underscore(self):
        class _Model(models.Model):
            pass

        self.assertEqual(
            _Model.check(),
            [
                Error(
                    "The model name '_Model' cannot start or end with an underscore "
                    "as it collides with the query lookup syntax.",
                    obj=_Model,
                    id="models.E023",
                )
            ],
        )

    def test_name_ending_with_underscore(self):
        class Model_(models.Model):
            pass

        self.assertEqual(
            Model_.check(),
            [
                Error(
                    "The model name 'Model_' cannot start or end with an underscore "
                    "as it collides with the query lookup syntax.",
                    obj=Model_,
                    id="models.E023",
                )
            ],
        )

    def test_name_contains_double_underscores(self):
        class Test__Model(models.Model):
            pass

        self.assertEqual(
            Test__Model.check(),
            [
                Error(
                    "The model name 'Test__Model' cannot contain double underscores "
                    "as it collides with the query lookup syntax.",
                    obj=Test__Model,
                    id="models.E024",
                )
            ],
        )

    def test_property_and_related_field_accessor_clash(self):
        class Model(models.Model):
            fk = models.ForeignKey("self", models.CASCADE)

        # Override related field accessor.
        Model.fk_id = property(lambda self: "ERROR")

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "The property 'fk_id' clashes with a related field accessor.",
                    obj=Model,
                    id="models.E025",
                )
            ],
        )

    def test_inherited_overriden_property_no_clash(self):
        class Cheese:
            @property
            def filling_id(self):
                pass

        class Sandwich(Cheese, models.Model):
            filling = models.ForeignKey("self", models.CASCADE)

        self.assertEqual(Sandwich.check(), [])

    def test_single_primary_key(self):
        class Model(models.Model):
            foo = models.IntegerField(primary_key=True)
            bar = models.IntegerField(primary_key=True)

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "The model cannot have more than one field with "
                    "'primary_key=True'.",
                    obj=Model,
                    id="models.E026",
                )
            ],
        )

    @override_settings(TEST_SWAPPED_MODEL_BAD_VALUE="not-a-model")
    def test_swappable_missing_app_name(self):
        class Model(models.Model):
            class Meta:
                swappable = "TEST_SWAPPED_MODEL_BAD_VALUE"

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'TEST_SWAPPED_MODEL_BAD_VALUE' is not of the form "
                    "'app_label.app_name'.",
                    id="models.E001",
                ),
            ],
        )

    @override_settings(TEST_SWAPPED_MODEL_BAD_MODEL="not_an_app.Target")
    def test_swappable_missing_app(self):
        class Model(models.Model):
            class Meta:
                swappable = "TEST_SWAPPED_MODEL_BAD_MODEL"

        self.assertEqual(
            Model.check(),
            [
                Error(
                    "'TEST_SWAPPED_MODEL_BAD_MODEL' references 'not_an_app.Target', "
                    "which has not been installed, or is abstract.",
                    id="models.E002",
                ),
            ],
        )

    def test_two_m2m_through_same_relationship(self):
        class Person(models.Model):
            pass

        class Group(models.Model):
            primary = models.ManyToManyField(
                Person, through="Membership", related_name="primary"
            )
            secondary = models.ManyToManyField(
                Person, through="Membership", related_name="secondary"
            )

        class Membership(models.Model):
            person = models.ForeignKey(Person, models.CASCADE)
            group = models.ForeignKey(Group, models.CASCADE)

        self.assertEqual(
            Group.check(),
            [
                Error(
                    "The model has two identical many-to-many relations through "
                    "the intermediate model 'invalid_models_tests.Membership'.",
                    obj=Group,
                    id="models.E003",
                )
            ],
        )

    def test_two_m2m_through_same_model_with_different_through_fields(self):
        class Country(models.Model):
            pass

        class ShippingMethod(models.Model):
            to_countries = models.ManyToManyField(
                Country,
                through="ShippingMethodPrice",
                through_fields=("method", "to_country"),
            )
            from_countries = models.ManyToManyField(
                Country,
                through="ShippingMethodPrice",
                through_fields=("method", "from_country"),
                related_name="+",
            )

        class ShippingMethodPrice(models.Model):
            method = models.ForeignKey(ShippingMethod, models.CASCADE)
            to_country = models.ForeignKey(Country, models.CASCADE)
            from_country = models.ForeignKey(Country, models.CASCADE)

        self.assertEqual(ShippingMethod.check(), [])

    def test_onetoone_with_parent_model(self):
        class Place(models.Model):
            pass

        class ParkingLot(Place):
            other_place = models.OneToOneField(
                Place, models.CASCADE, related_name="other_parking"
            )

        self.assertEqual(ParkingLot.check(), [])

    def test_onetoone_with_explicit_parent_link_parent_model(self):
        class Place(models.Model):
            pass

        class ParkingLot(Place):
            place = models.OneToOneField(
                Place, models.CASCADE, parent_link=True, primary_key=True
            )
            other_place = models.OneToOneField(
                Place, models.CASCADE, related_name="other_parking"
            )

        self.assertEqual(ParkingLot.check(), [])

    def test_m2m_table_name_clash(self):
        class Foo(models.Model):
            bar = models.ManyToManyField("Bar", db_table="myapp_bar")

            class Meta:
                db_table = "myapp_foo"

        class Bar(models.Model):
            class Meta:
                db_table = "myapp_bar"

        self.assertEqual(
            Foo.check(),
            [
                Error(
                    "The field's intermediary table 'myapp_bar' clashes with the "
                    "table name of 'invalid_models_tests.Bar'.",
                    obj=Foo._meta.get_field("bar"),
                    id="fields.E340",
                )
            ],
        )

    @override_settings(
        DATABASE_ROUTERS=["invalid_models_tests.test_models.EmptyRouter"]
    )
    def test_m2m_table_name_clash_database_routers_installed(self):
        class Foo(models.Model):
            bar = models.ManyToManyField("Bar", db_table="myapp_bar")

            class Meta:
                db_table = "myapp_foo"

        class Bar(models.Model):
            class Meta:
                db_table = "myapp_bar"

        self.assertEqual(
            Foo.check(),
            [
                Warning(
                    "The field's intermediary table 'myapp_bar' clashes with the "
                    "table name of 'invalid_models_tests.Bar'.",
                    obj=Foo._meta.get_field("bar"),
                    hint=(
                        "You have configured settings.DATABASE_ROUTERS. Verify "
                        "that the table of 'invalid_models_tests.Bar' is "
                        "correctly routed to a separate database."
                    ),
                    id="fields.W344",
                ),
            ],
        )

    def test_m2m_field_table_name_clash(self):
        class Foo(models.Model):
            pass

        class Bar(models.Model):
            foos = models.ManyToManyField(Foo, db_table="clash")

        class Baz(models.Model):
            foos = models.ManyToManyField(Foo, db_table="clash")

        self.assertEqual(
            Bar.check() + Baz.check(),
            [
                Error(
                    "The field's intermediary table 'clash' clashes with the "
                    "table name of 'invalid_models_tests.Baz.foos'.",
                    obj=Bar._meta.get_field("foos"),
                    id="fields.E340",
                ),
                Error(
                    "The field's intermediary table 'clash' clashes with the "
                    "table name of 'invalid_models_tests.Bar.foos'.",
                    obj=Baz._meta.get_field("foos"),
                    id="fields.E340",
                ),
            ],
        )

    @override_settings(
        DATABASE_ROUTERS=["invalid_models_tests.test_models.EmptyRouter"]
    )
    def test_m2m_field_table_name_clash_database_routers_installed(self):
        class Foo(models.Model):
            pass

        class Bar(models.Model):
            foos = models.ManyToManyField(Foo, db_table="clash")

        class Baz(models.Model):
            foos = models.ManyToManyField(Foo, db_table="clash")

        self.assertEqual(
            Bar.check() + Baz.check(),
            [
                Warning(
                    "The field's intermediary table 'clash' clashes with the "
                    "table name of 'invalid_models_tests.%s.foos'." % clashing_model,
                    obj=model_cls._meta.get_field("foos"),
                    hint=(
                        "You have configured settings.DATABASE_ROUTERS. Verify "
                        "that the table of 'invalid_models_tests.%s.foos' is "
                        "correctly routed to a separate database." % clashing_model
                    ),
                    id="fields.W344",
                )
                for model_cls, clashing_model in [(Bar, "Baz"), (Baz, "Bar")]
            ],
        )

    def test_m2m_autogenerated_table_name_clash(self):
        class Foo(models.Model):
            class Meta:
                db_table = "bar_foos"

        class Bar(models.Model):
            # The autogenerated `db_table` will be bar_foos.
            foos = models.ManyToManyField(Foo)

            class Meta:
                db_table = "bar"

        self.assertEqual(
            Bar.check(),
            [
                Error(
                    "The field's intermediary table 'bar_foos' clashes with the "
                    "table name of 'invalid_models_tests.Foo'.",
                    obj=Bar._meta.get_field("foos"),
                    id="fields.E340",
                )
            ],
        )

    @override_settings(
        DATABASE_ROUTERS=["invalid_models_tests.test_models.EmptyRouter"]
    )
    def test_m2m_autogenerated_table_name_clash_database_routers_installed(self):
        class Foo(models.Model):
            class Meta:
                db_table = "bar_foos"

        class Bar(models.Model):
            # The autogenerated db_table is bar_foos.
            foos = models.ManyToManyField(Foo)

            class Meta:
                db_table = "bar"

        self.assertEqual(
            Bar.check(),
            [
                Warning(
                    "The field's intermediary table 'bar_foos' clashes with the "
                    "table name of 'invalid_models_tests.Foo'.",
                    obj=Bar._meta.get_field("foos"),
                    hint=(
                        "You have configured settings.DATABASE_ROUTERS. Verify "
                        "that the table of 'invalid_models_tests.Foo' is "
                        "correctly routed to a separate database."
                    ),
                    id="fields.W344",
                ),
            ],
        )

    def test_m2m_unmanaged_shadow_models_not_checked(self):
        class A1(models.Model):
            pass

        class C1(models.Model):
            mm_a = models.ManyToManyField(A1, db_table="d1")

        # Unmanaged models that shadow the above models. Reused table names
        # shouldn't be flagged by any checks.
        class A2(models.Model):
            class Meta:
                managed = False

        class C2(models.Model):
            mm_a = models.ManyToManyField(A2, through="Intermediate")

            class Meta:
                managed = False

        class Intermediate(models.Model):
            a2 = models.ForeignKey(A2, models.CASCADE, db_column="a1_id")
            c2 = models.ForeignKey(C2, models.CASCADE, db_column="c1_id")

            class Meta:
                db_table = "d1"
                managed = False

        self.assertEqual(C1.check(), [])
        self.assertEqual(C2.check(), [])

    def test_m2m_to_concrete_and_proxy_allowed(self):
        class A(models.Model):
            pass

        class Through(models.Model):
            a = models.ForeignKey("A", models.CASCADE)
            c = models.ForeignKey("C", models.CASCADE)

        class ThroughProxy(Through):
            class Meta:
                proxy = True

        class C(models.Model):
            mm_a = models.ManyToManyField(A, through=Through)
            mm_aproxy = models.ManyToManyField(
                A, through=ThroughProxy, related_name="proxied_m2m"
            )

        self.assertEqual(C.check(), [])

    @isolate_apps("django.contrib.auth", kwarg_name="apps")
    def test_lazy_reference_checks(self, apps):
        class DummyModel(models.Model):
            author = models.ForeignKey("Author", models.CASCADE)

            class Meta:
                app_label = "invalid_models_tests"

        class DummyClass:
            def __call__(self, **kwargs):
                pass

            def dummy_method(self):
                pass

        def dummy_function(*args, **kwargs):
            pass

        apps.lazy_model_operation(dummy_function, ("auth", "imaginarymodel"))
        apps.lazy_model_operation(dummy_function, ("fanciful_app", "imaginarymodel"))

        post_init.connect(dummy_function, sender="missing-app.Model", apps=apps)
        post_init.connect(DummyClass(), sender="missing-app.Model", apps=apps)
        post_init.connect(
            DummyClass().dummy_method, sender="missing-app.Model", apps=apps
        )

        self.assertEqual(
            _check_lazy_references(apps),
            [
                Error(
                    "%r contains a lazy reference to auth.imaginarymodel, "
                    "but app 'auth' doesn't provide model 'imaginarymodel'."
                    % dummy_function,
                    obj=dummy_function,
                    id="models.E022",
                ),
                Error(
                    "%r contains a lazy reference to fanciful_app.imaginarymodel, "
                    "but app 'fanciful_app' isn't installed." % dummy_function,
                    obj=dummy_function,
                    id="models.E022",
                ),
                Error(
                    "An instance of class 'DummyClass' was connected to "
                    "the 'post_init' signal with a lazy reference to the sender "
                    "'missing-app.model', but app 'missing-app' isn't installed.",
                    hint=None,
                    obj="invalid_models_tests.test_models",
                    id="signals.E001",
                ),
                Error(
                    "Bound method 'DummyClass.dummy_method' was connected to the "
                    "'post_init' signal with a lazy reference to the sender "
                    "'missing-app.model', but app 'missing-app' isn't installed.",
                    hint=None,
                    obj="invalid_models_tests.test_models",
                    id="signals.E001",
                ),
                Error(
                    "The field invalid_models_tests.DummyModel.author was declared "
                    "with a lazy reference to 'invalid_models_tests.author', but app "
                    "'invalid_models_tests' isn't installed.",
                    hint=None,
                    obj=DummyModel.author.field,
                    id="fields.E307",
                ),
                Error(
                    "The function 'dummy_function' was connected to the 'post_init' "
                    "signal with a lazy reference to the sender "
                    "'missing-app.model', but app 'missing-app' isn't installed.",
                    hint=None,
                    obj="invalid_models_tests.test_models",
                    id="signals.E001",
                ),
            ],
        )


@isolate_apps("invalid_models_tests")
class DbTableCommentTests(TestCase):
    def test_db_table_comment(self):
        class Model(models.Model):
            class Meta:
                db_table_comment = "Table comment"

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_comments
            else [
                Warning(
                    f"{connection.display_name} does not support comments on tables "
                    f"(db_table_comment).",
                    obj=Model,
                    id="models.W046",
                ),
            ]
        )
        self.assertEqual(errors, expected)

    def test_db_table_comment_required_db_features(self):
        class Model(models.Model):
            class Meta:
                db_table_comment = "Table comment"
                required_db_features = {"supports_comments"}

        self.assertEqual(Model.check(databases=self.databases), [])


class MultipleAutoFieldsTests(TestCase):
    def test_multiple_autofields(self):
        msg = (
            "Model invalid_models_tests.MultipleAutoFields can't have more "
            "than one auto-generated field."
        )
        with self.assertRaisesMessage(ValueError, msg):

            class MultipleAutoFields(models.Model):
                auto1 = models.AutoField(primary_key=True)
                auto2 = models.AutoField(primary_key=True)


@isolate_apps("invalid_models_tests")
class JSONFieldTests(TestCase):
    @skipUnlessDBFeature("supports_json_field")
    def test_ordering_pointing_to_json_field_value(self):
        class Model(models.Model):
            field = models.JSONField()

            class Meta:
                ordering = ["field__value"]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_check_jsonfield(self):
        class Model(models.Model):
            field = models.JSONField()

        error = Error(
            "%s does not support JSONFields." % connection.display_name,
            obj=Model,
            id="fields.E180",
        )
        expected = [] if connection.features.supports_json_field else [error]
        self.assertEqual(Model.check(databases=self.databases), expected)

    def test_check_jsonfield_required_db_features(self):
        class Model(models.Model):
            field = models.JSONField()

            class Meta:
                required_db_features = {"supports_json_field"}

        self.assertEqual(Model.check(databases=self.databases), [])


@isolate_apps("invalid_models_tests")
class ConstraintsTests(TestCase):
    def test_check_constraints(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        condition=models.Q(age__gte=18), name="is_adult"
                    )
                ]

        errors = Model.check(databases=self.databases)
        warn = Warning(
            "%s does not support check constraints." % connection.display_name,
            hint=(
                "A constraint won't be created. Silence this warning if you "
                "don't care about it."
            ),
            obj=Model,
            id="models.W027",
        )
        expected = (
            [] if connection.features.supports_table_check_constraints else [warn]
        )
        self.assertCountEqual(errors, expected)

    def test_check_constraints_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_table_check_constraints"}
                constraints = [
                    models.CheckConstraint(
                        condition=models.Q(age__gte=18), name="is_adult"
                    )
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_check_constraint_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                required_db_features = {"supports_table_check_constraints"}
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(missing_field=2),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            (
                [
                    Error(
                        "'constraints' refers to the nonexistent field "
                        "'missing_field'.",
                        obj=Model,
                        id="models.E012",
                    ),
                ]
                if connection.features.supports_table_check_constraints
                else []
            ),
        )

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_reverse_fk(self):
        class Model(models.Model):
            parent = models.ForeignKey("self", models.CASCADE, related_name="parents")

            class Meta:
                constraints = [
                    models.CheckConstraint(name="name", condition=models.Q(parents=3)),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'parents'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_reverse_o2o(self):
        class Model(models.Model):
            parent = models.OneToOneField("self", models.CASCADE)

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(model__isnull=True),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'model'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                constraints = [
                    models.CheckConstraint(name="name", condition=models.Q(m2m=2)),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_fk(self):
        class Target(models.Model):
            pass

        class Model(models.Model):
            fk_1 = models.ForeignKey(Target, models.CASCADE, related_name="target_1")
            fk_2 = models.ForeignKey(Target, models.CASCADE, related_name="target_2")

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(fk_1_id=2) | models.Q(fk_2=2),
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_pk(self):
        class Model(models.Model):
            age = models.SmallIntegerField()

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(pk__gt=5) & models.Q(age__gt=models.F("pk")),
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_non_local_field(self):
        class Parent(models.Model):
            field1 = models.IntegerField()

        class Child(Parent):
            pass

            class Meta:
                constraints = [
                    models.CheckConstraint(name="name", condition=models.Q(field1=1)),
                ]

        self.assertEqual(
            Child.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to field 'field1' which is not local to "
                    "model 'Child'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Child,
                    id="models.E016",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_joined_fields(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)
            field1 = models.PositiveSmallIntegerField()
            field2 = models.PositiveSmallIntegerField()
            field3 = models.PositiveSmallIntegerField()
            parent = models.ForeignKey("self", models.CASCADE)
            previous = models.OneToOneField("self", models.CASCADE, related_name="next")

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name1",
                        condition=models.Q(
                            field1__lt=models.F("parent__field1")
                            + models.F("parent__field2")
                        ),
                    ),
                    models.CheckConstraint(
                        name="name2", condition=models.Q(name=Lower("parent__name"))
                    ),
                    models.CheckConstraint(
                        name="name3",
                        condition=models.Q(parent__field3=models.F("field1")),
                    ),
                    models.CheckConstraint(
                        name="name4",
                        condition=models.Q(name=Lower("previous__name")),
                    ),
                ]

        joined_fields = [
            "parent__field1",
            "parent__field2",
            "parent__field3",
            "parent__name",
            "previous__name",
        ]
        errors = Model.check(databases=self.databases)
        expected_errors = [
            Error(
                "'constraints' refers to the joined field '%s'." % field_name,
                obj=Model,
                id="models.E041",
            )
            for field_name in joined_fields
        ]
        self.assertCountEqual(errors, expected_errors)

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_joined_fields_complex_check(self):
        class Model(models.Model):
            name = models.PositiveSmallIntegerField()
            field1 = models.PositiveSmallIntegerField()
            field2 = models.PositiveSmallIntegerField()
            parent = models.ForeignKey("self", models.CASCADE)

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(
                            (
                                models.Q(name="test")
                                & models.Q(field1__lt=models.F("parent__field1"))
                            )
                            | (
                                models.Q(name__startswith=Lower("parent__name"))
                                & models.Q(
                                    field1__gte=(
                                        models.F("parent__field1")
                                        + models.F("parent__field2")
                                    )
                                )
                            )
                        )
                        | (models.Q(name="test1")),
                    ),
                ]

        joined_fields = ["parent__field1", "parent__field2", "parent__name"]
        errors = Model.check(databases=self.databases)
        expected_errors = [
            Error(
                "'constraints' refers to the joined field '%s'." % field_name,
                obj=Model,
                id="models.E041",
            )
            for field_name in joined_fields
        ]
        self.assertCountEqual(errors, expected_errors)

    def test_check_constraint_raw_sql_check(self):
        class Model(models.Model):
            class Meta:
                required_db_features = {"supports_table_check_constraints"}
                constraints = [
                    models.CheckConstraint(
                        condition=models.Q(id__gt=0), name="q_check"
                    ),
                    models.CheckConstraint(
                        condition=models.ExpressionWrapper(
                            models.Q(price__gt=20),
                            output_field=models.BooleanField(),
                        ),
                        name="expression_wrapper_check",
                    ),
                    models.CheckConstraint(
                        condition=models.expressions.RawSQL(
                            "id = 0",
                            params=(),
                            output_field=models.BooleanField(),
                        ),
                        name="raw_sql_check",
                    ),
                    models.CheckConstraint(
                        condition=models.Q(
                            models.ExpressionWrapper(
                                models.Q(
                                    models.expressions.RawSQL(
                                        "id = 0",
                                        params=(),
                                        output_field=models.BooleanField(),
                                    )
                                ),
                                output_field=models.BooleanField(),
                            )
                        ),
                        name="nested_raw_sql_check",
                    ),
                ]

        expected_warnings = (
            [
                Warning(
                    "Check constraint 'raw_sql_check' contains RawSQL() expression and "
                    "won't be validated during the model full_clean().",
                    hint="Silence this warning if you don't care about it.",
                    obj=Model,
                    id="models.W045",
                ),
                Warning(
                    "Check constraint 'nested_raw_sql_check' contains RawSQL() "
                    "expression and won't be validated during the model full_clean().",
                    hint="Silence this warning if you don't care about it.",
                    obj=Model,
                    id="models.W045",
                ),
            ]
            if connection.features.supports_table_check_constraints
            else []
        )
        self.assertEqual(Model.check(databases=self.databases), expected_warnings)

    @skipUnlessDBFeature("supports_table_check_constraints")
    def test_check_constraint_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                constraints = [
                    models.CheckConstraint(
                        name="name",
                        condition=models.Q(pk__gt=(7, "focal")),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_unique_constraint_with_condition(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_gte_100",
                        condition=models.Q(age__gte=100),
                    ),
                ]

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_partial_indexes
            else [
                Warning(
                    "%s does not support unique constraints with conditions."
                    % connection.display_name,
                    hint=(
                        "A constraint won't be created. Silence this warning if "
                        "you don't care about it."
                    ),
                    obj=Model,
                    id="models.W036",
                ),
            ]
        )
        self.assertEqual(errors, expected)

    def test_unique_constraint_with_condition_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_partial_indexes"}
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_gte_100",
                        condition=models.Q(age__gte=100),
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_unique_constraint_condition_pointing_to_missing_field(self):
        class Model(models.Model):
            age = models.SmallIntegerField()

            class Meta:
                required_db_features = {"supports_partial_indexes"}
                constraints = [
                    models.UniqueConstraint(
                        name="name",
                        fields=["age"],
                        condition=models.Q(missing_field=2),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            (
                [
                    Error(
                        "'constraints' refers to the nonexistent field "
                        "'missing_field'.",
                        obj=Model,
                        id="models.E012",
                    ),
                ]
                if connection.features.supports_partial_indexes
                else []
            ),
        )

    def test_unique_constraint_condition_pointing_to_joined_fields(self):
        class Model(models.Model):
            age = models.SmallIntegerField()
            parent = models.ForeignKey("self", models.CASCADE)

            class Meta:
                required_db_features = {"supports_partial_indexes"}
                constraints = [
                    models.UniqueConstraint(
                        name="name",
                        fields=["age"],
                        condition=models.Q(parent__age__lt=2),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            (
                [
                    Error(
                        "'constraints' refers to the joined field 'parent__age__lt'.",
                        obj=Model,
                        id="models.E041",
                    )
                ]
                if connection.features.supports_partial_indexes
                else []
            ),
        )

    def test_unique_constraint_pointing_to_reverse_o2o(self):
        class Model(models.Model):
            parent = models.OneToOneField("self", models.CASCADE)

            class Meta:
                required_db_features = {"supports_partial_indexes"}
                constraints = [
                    models.UniqueConstraint(
                        fields=["parent"],
                        name="name",
                        condition=models.Q(model__isnull=True),
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            (
                [
                    Error(
                        "'constraints' refers to the nonexistent field 'model'.",
                        obj=Model,
                        id="models.E012",
                    ),
                ]
                if connection.features.supports_partial_indexes
                else []
            ),
        )

    def test_deferrable_unique_constraint(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_deferrable",
                        deferrable=models.Deferrable.DEFERRED,
                    ),
                ]

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_deferrable_unique_constraints
            else [
                Warning(
                    "%s does not support deferrable unique constraints."
                    % connection.display_name,
                    hint=(
                        "A constraint won't be created. Silence this warning if "
                        "you don't care about it."
                    ),
                    obj=Model,
                    id="models.W038",
                ),
            ]
        )
        self.assertEqual(errors, expected)

    def test_deferrable_unique_constraint_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_deferrable_unique_constraints"}
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_deferrable",
                        deferrable=models.Deferrable.IMMEDIATE,
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_unique_constraint_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                constraints = [
                    models.UniqueConstraint(fields=["missing_field"], name="name")
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    def test_unique_constraint_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                constraints = [models.UniqueConstraint(fields=["m2m"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    def test_unique_constraint_pointing_to_non_local_field(self):
        class Parent(models.Model):
            field1 = models.IntegerField()

        class Child(Parent):
            field2 = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(fields=["field2", "field1"], name="name"),
                ]

        self.assertEqual(
            Child.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to field 'field1' which is not local to "
                    "model 'Child'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Child,
                    id="models.E016",
                ),
            ],
        )

    def test_unique_constraint_pointing_to_fk(self):
        class Target(models.Model):
            pass

        class Model(models.Model):
            fk_1 = models.ForeignKey(Target, models.CASCADE, related_name="target_1")
            fk_2 = models.ForeignKey(Target, models.CASCADE, related_name="target_2")

            class Meta:
                constraints = [
                    models.UniqueConstraint(fields=["fk_1_id", "fk_2"], name="name"),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_unique_constraint_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                constraints = [models.UniqueConstraint(fields=["pk"], name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_unique_constraint_with_include(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_include_id",
                        include=["id"],
                    ),
                ]

        errors = Model.check(databases=self.databases)
        expected = (
            []
            if connection.features.supports_covering_indexes
            else [
                Warning(
                    "%s does not support unique constraints with non-key columns."
                    % connection.display_name,
                    hint=(
                        "A constraint won't be created. Silence this warning if "
                        "you don't care about it."
                    ),
                    obj=Model,
                    id="models.W039",
                ),
            ]
        )
        self.assertEqual(errors, expected)

    def test_unique_constraint_with_include_required_db_features(self):
        class Model(models.Model):
            age = models.IntegerField()

            class Meta:
                required_db_features = {"supports_covering_indexes"}
                constraints = [
                    models.UniqueConstraint(
                        fields=["age"],
                        name="unique_age_include_id",
                        include=["id"],
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_unique_constraint_include_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["id"],
                        include=["missing_field"],
                        name="name",
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_unique_constraint_include_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["id"],
                        include=["m2m"],
                        name="name",
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_unique_constraint_include_pointing_to_non_local_field(self):
        class Parent(models.Model):
            field1 = models.IntegerField()

        class Child(Parent):
            field2 = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["field2"],
                        include=["field1"],
                        name="name",
                    ),
                ]

        self.assertEqual(
            Child.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to field 'field1' which is not local to "
                    "model 'Child'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Child,
                    id="models.E016",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_unique_constraint_include_pointing_to_fk(self):
        class Target(models.Model):
            pass

        class Model(models.Model):
            fk_1 = models.ForeignKey(Target, models.CASCADE, related_name="target_1")
            fk_2 = models.ForeignKey(Target, models.CASCADE, related_name="target_2")

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["id"],
                        include=["fk_1_id", "fk_2"],
                        name="name",
                    ),
                ]

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_covering_indexes")
    def test_unique_constraint_include_pointing_to_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["version"],
                        include=["pk"],
                        name="name",
                    ),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )

    def test_func_unique_constraint(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                constraints = [
                    models.UniqueConstraint(Lower("name"), name="lower_name_uq"),
                ]

        warn = Warning(
            "%s does not support unique constraints on expressions."
            % connection.display_name,
            hint=(
                "A constraint won't be created. Silence this warning if you "
                "don't care about it."
            ),
            obj=Model,
            id="models.W044",
        )
        expected = [] if connection.features.supports_expression_indexes else [warn]
        self.assertEqual(Model.check(databases=self.databases), expected)

    def test_func_unique_constraint_required_db_features(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                constraints = [
                    models.UniqueConstraint(Lower("name"), name="lower_name_unq"),
                ]
                required_db_features = {"supports_expression_indexes"}

        self.assertEqual(Model.check(databases=self.databases), [])

    def test_unique_constraint_nulls_distinct(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["name"],
                        name="name_uq_distinct_null",
                        nulls_distinct=True,
                    ),
                ]

        warn = Warning(
            f"{connection.display_name} does not support unique constraints with nulls "
            "distinct.",
            hint=(
                "A constraint won't be created. Silence this warning if you don't care "
                "about it."
            ),
            obj=Model,
            id="models.W047",
        )
        expected = (
            []
            if connection.features.supports_nulls_distinct_unique_constraints
            else [warn]
        )
        self.assertEqual(Model.check(databases=self.databases), expected)

    def test_unique_constraint_nulls_distinct_required_db_features(self):
        class Model(models.Model):
            name = models.CharField(max_length=10)

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        fields=["name"],
                        name="name_uq_distinct_null",
                        nulls_distinct=True,
                    ),
                ]
                required_db_features = {"supports_nulls_distinct_unique_constraints"}

        self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_expression_custom_lookup(self):
        class Model(models.Model):
            height = models.IntegerField()
            weight = models.IntegerField()

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        models.F("height")
                        / (models.F("weight__abs") + models.Value(5)),
                        name="name",
                    ),
                ]

        with register_lookup(models.IntegerField, Abs):
            self.assertEqual(Model.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_to_missing_field(self):
        class Model(models.Model):
            class Meta:
                constraints = [
                    models.UniqueConstraint(Lower("missing_field").desc(), name="name"),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_to_missing_field_nested(self):
        class Model(models.Model):
            class Meta:
                constraints = [
                    models.UniqueConstraint(Abs(Round("missing_field")), name="name"),
                ]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to the nonexistent field 'missing_field'.",
                    obj=Model,
                    id="models.E012",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_to_m2m_field(self):
        class Model(models.Model):
            m2m = models.ManyToManyField("self")

            class Meta:
                constraints = [models.UniqueConstraint(Lower("m2m"), name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a ManyToManyField 'm2m', but "
                    "ManyToManyFields are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E013",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_to_non_local_field(self):
        class Foo(models.Model):
            field1 = models.CharField(max_length=15)

        class Bar(Foo):
            class Meta:
                constraints = [models.UniqueConstraint(Lower("field1"), name="name")]

        self.assertEqual(
            Bar.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to field 'field1' which is not local to "
                    "model 'Bar'.",
                    hint="This issue may be caused by multi-table inheritance.",
                    obj=Bar,
                    id="models.E016",
                ),
            ],
        )

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_to_fk(self):
        class Foo(models.Model):
            id = models.CharField(primary_key=True, max_length=255)

        class Bar(models.Model):
            foo_1 = models.ForeignKey(Foo, models.CASCADE, related_name="bar_1")
            foo_2 = models.ForeignKey(Foo, models.CASCADE, related_name="bar_2")

            class Meta:
                constraints = [
                    models.UniqueConstraint(
                        Lower("foo_1_id"),
                        Lower("foo_2"),
                        name="name",
                    ),
                ]

        self.assertEqual(Bar.check(databases=self.databases), [])

    @skipUnlessDBFeature("supports_expression_indexes")
    def test_func_unique_constraint_pointing_composite_primary_key(self):
        class Model(models.Model):
            pk = models.CompositePrimaryKey("version", "name")
            version = models.IntegerField()
            name = models.CharField(max_length=20)

            class Meta:
                constraints = [models.UniqueConstraint(Abs("pk"), name="name")]

        self.assertEqual(
            Model.check(databases=self.databases),
            [
                Error(
                    "'constraints' refers to a CompositePrimaryKey 'pk', but "
                    "CompositePrimaryKeys are not permitted in 'constraints'.",
                    obj=Model,
                    id="models.E048",
                ),
            ],
        )
