import datetime
import itertools
import unittest
from copy import copy

from django.db import (
    DatabaseError, IntegrityError, OperationalError, connection,
)
from django.db.models import Model
from django.db.models.fields import (
    BigIntegerField, BinaryField, BooleanField, CharField, DateTimeField,
    IntegerField, PositiveIntegerField, SlugField, TextField,
)
from django.db.models.fields.related import (
    ForeignKey, ManyToManyField, OneToOneField,
)
from django.db.transaction import atomic
from django.test import TransactionTestCase, skipIfDBFeature

from .fields import CustomManyToManyField, InheritedManyToManyField
from .models import (
    Author, AuthorWithDefaultHeight, AuthorWithEvenLongerName, Book, BookWeak,
    BookWithLongName, BookWithO2O, BookWithSlug, Note, Tag, TagIndexed,
    TagM2MTest, TagUniqueRename, Thing, UniqueTest, new_apps,
)


class SchemaTests(TransactionTestCase):
    """
    Tests that the schema-alteration code works correctly.

    Be aware that these tests are more liable than most to false results,
    as sometimes the code to check if a test has worked is almost as complex
    as the code it is testing.
    """

    available_apps = []

    models = [
        Author, AuthorWithDefaultHeight, AuthorWithEvenLongerName, Book,
        BookWeak, BookWithLongName, BookWithO2O, BookWithSlug, Note, Tag,
        TagIndexed, TagM2MTest, TagUniqueRename, Thing, UniqueTest,
    ]

    # Utility functions

    def setUp(self):
        # local_models should contain test dependent model classes that will be
        # automatically removed from the app cache on test tear down.
        self.local_models = []

    def tearDown(self):
        # Delete any tables made for our models
        self.delete_tables()
        new_apps.clear_cache()
        for model in new_apps.get_models():
            model._meta._expire_cache()
        if 'schema' in new_apps.all_models:
            for model in self.local_models:
                del new_apps.all_models['schema'][model._meta.model_name]

    def delete_tables(self):
        "Deletes all model tables for our models for a clean test environment"
        with connection.cursor() as cursor:
            connection.disable_constraint_checking()
            table_names = connection.introspection.table_names(cursor)
            for model in itertools.chain(SchemaTests.models, self.local_models):
                # Remove any M2M tables first
                for field in model._meta.local_many_to_many:
                    with atomic():
                        tbl = field.rel.through._meta.db_table
                        if tbl in table_names:
                            cursor.execute(connection.schema_editor().sql_delete_table % {
                                "table": connection.ops.quote_name(tbl),
                            })
                            table_names.remove(tbl)
                # Then remove the main tables
                with atomic():
                    tbl = model._meta.db_table
                    if tbl in table_names:
                        cursor.execute(connection.schema_editor().sql_delete_table % {
                            "table": connection.ops.quote_name(tbl),
                        })
                        table_names.remove(tbl)
        connection.enable_constraint_checking()

    def column_classes(self, model):
        with connection.cursor() as cursor:
            columns = {
                d[0]: (connection.introspection.get_field_type(d[1], d), d)
                for d in connection.introspection.get_table_description(
                    cursor,
                    model._meta.db_table,
                )
            }
        # SQLite has a different format for field_type
        for name, (type, desc) in columns.items():
            if isinstance(type, tuple):
                columns[name] = (type[0], desc)
        # SQLite also doesn't error properly
        if not columns:
            raise DatabaseError("Table does not exist (empty pragma)")
        return columns

    def get_indexes(self, table):
        """
        Get the indexes on the table using a new cursor.
        """
        with connection.cursor() as cursor:
            return connection.introspection.get_indexes(cursor, table)

    def get_constraints(self, table):
        """
        Get the constraints on a table using a new cursor.
        """
        with connection.cursor() as cursor:
            return connection.introspection.get_constraints(cursor, table)

    # Tests

    def test_creation_deletion(self):
        """
        Tries creating a model's table, and then deleting it.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Check that it's there
        list(Author.objects.all())
        # Clean up that table
        with connection.schema_editor() as editor:
            editor.delete_model(Author)
        # Check that it's gone
        self.assertRaises(
            DatabaseError,
            lambda: list(Author.objects.all()),
        )

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_fk(self):
        "Tests that creating tables out of FK order, then repointing, works"
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Book)
            editor.create_model(Author)
            editor.create_model(Tag)
        # Check that initial tables are there
        list(Author.objects.all())
        list(Book.objects.all())
        # Make sure the FK constraint is present
        with self.assertRaises(IntegrityError):
            Book.objects.create(
                author_id=1,
                title="Much Ado About Foreign Keys",
                pub_date=datetime.datetime.now(),
            )
        # Repoint the FK constraint
        old_field = Book._meta.get_field("author")
        new_field = ForeignKey(Tag)
        new_field.set_attributes_from_name("author")
        with connection.schema_editor() as editor:
            editor.alter_field(Book, old_field, new_field, strict=True)
        # Make sure the new FK constraint is present
        constraints = self.get_constraints(Book._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["author_id"] and details['foreign_key']:
                self.assertEqual(details['foreign_key'], ('schema_tag', 'id'))
                break
        else:
            self.fail("No FK constraint for author_id found")

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_fk_db_constraint(self):
        "Tests that the db_constraint parameter is respected"
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Tag)
            editor.create_model(Author)
            editor.create_model(BookWeak)
        # Check that initial tables are there
        list(Author.objects.all())
        list(Tag.objects.all())
        list(BookWeak.objects.all())
        # Check that BookWeak doesn't have an FK constraint
        constraints = self.get_constraints(BookWeak._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["author_id"] and details['foreign_key']:
                self.fail("FK constraint for author_id found")
        # Make a db_constraint=False FK
        new_field = ForeignKey(Tag, db_constraint=False)
        new_field.set_attributes_from_name("tag")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Make sure no FK constraint is present
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["tag_id"] and details['foreign_key']:
                self.fail("FK constraint for tag_id found")
        # Alter to one with a constraint
        new_field2 = ForeignKey(Tag)
        new_field2.set_attributes_from_name("tag")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, new_field, new_field2, strict=True)
        # Make sure the new FK constraint is present
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["tag_id"] and details['foreign_key']:
                self.assertEqual(details['foreign_key'], ('schema_tag', 'id'))
                break
        else:
            self.fail("No FK constraint for tag_id found")
        # Alter to one without a constraint again
        new_field2 = ForeignKey(Tag)
        new_field2.set_attributes_from_name("tag")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, new_field2, new_field, strict=True)
        # Make sure no FK constraint is present
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["tag_id"] and details['foreign_key']:
                self.fail("FK constraint for tag_id found")

    def _test_m2m_db_constraint(self, M2MFieldClass):
        class LocalAuthorWithM2M(Model):
            name = CharField(max_length=255)

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [LocalAuthorWithM2M]

        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Tag)
            editor.create_model(LocalAuthorWithM2M)
        # Check that initial tables are there
        list(LocalAuthorWithM2M.objects.all())
        list(Tag.objects.all())
        # Make a db_constraint=False FK
        new_field = M2MFieldClass(Tag, related_name="authors", db_constraint=False)
        new_field.contribute_to_class(LocalAuthorWithM2M, "tags")
        # Add the field
        with connection.schema_editor() as editor:
            editor.add_field(LocalAuthorWithM2M, new_field)
        # Make sure no FK constraint is present
        constraints = self.get_constraints(new_field.rel.through._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["tag_id"] and details['foreign_key']:
                self.fail("FK constraint for tag_id found")

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_m2m_db_constraint(self):
        self._test_m2m_db_constraint(ManyToManyField)

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_m2m_db_constraint_custom(self):
        self._test_m2m_db_constraint(CustomManyToManyField)

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_m2m_db_constraint_inherited(self):
        self._test_m2m_db_constraint(InheritedManyToManyField)

    def test_add_field(self):
        """
        Tests adding fields to models
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure there's no age field
        columns = self.column_classes(Author)
        self.assertNotIn("age", columns)
        # Add the new field
        new_field = IntegerField(null=True)
        new_field.set_attributes_from_name("age")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertEqual(columns['age'][0], "IntegerField")
        self.assertEqual(columns['age'][1][6], True)

    def test_add_field_temp_default(self):
        """
        Tests adding fields to models with a temporary default
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure there's no age field
        columns = self.column_classes(Author)
        self.assertNotIn("age", columns)
        # Add some rows of data
        Author.objects.create(name="Andrew", height=30)
        Author.objects.create(name="Andrea")
        # Add a not-null field
        new_field = CharField(max_length=30, default="Godwin")
        new_field.set_attributes_from_name("surname")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertEqual(columns['surname'][0], "CharField")
        self.assertEqual(columns['surname'][1][6],
                         connection.features.interprets_empty_strings_as_nulls)

    def test_add_field_temp_default_boolean(self):
        """
        Tests adding fields to models with a temporary default where
        the default is False. (#21783)
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure there's no age field
        columns = self.column_classes(Author)
        self.assertNotIn("age", columns)
        # Add some rows of data
        Author.objects.create(name="Andrew", height=30)
        Author.objects.create(name="Andrea")
        # Add a not-null field
        new_field = BooleanField(default=False)
        new_field.set_attributes_from_name("awesome")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        # BooleanField are stored as TINYINT(1) on MySQL.
        field_type = columns['awesome'][0]
        self.assertEqual(field_type, connection.features.introspected_boolean_field_type(new_field, created_separately=True))

    def test_add_field_default_transform(self):
        """
        Tests adding fields to models with a default that is not directly
        valid in the database (#22581)
        """

        class TestTransformField(IntegerField):

            # Weird field that saves the count of items in its value
            def get_default(self):
                return self.default

            def get_prep_value(self, value):
                if value is None:
                    return 0
                return len(value)

        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Add some rows of data
        Author.objects.create(name="Andrew", height=30)
        Author.objects.create(name="Andrea")
        # Add the field with a default it needs to cast (to string in this case)
        new_field = TestTransformField(default={1: 2})
        new_field.set_attributes_from_name("thing")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure the field is there
        columns = self.column_classes(Author)
        field_type, field_info = columns['thing']
        self.assertEqual(field_type, 'IntegerField')
        # Make sure the values were transformed correctly
        self.assertEqual(Author.objects.extra(where=["thing = 1"]).count(), 2)

    def test_add_field_binary(self):
        """
        Tests binary fields get a sane default (#22851)
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Add the new field
        new_field = BinaryField(blank=True)
        new_field.set_attributes_from_name("bits")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        # MySQL annoyingly uses the same backend, so it'll come back as one of
        # these two types.
        self.assertIn(columns['bits'][0], ("BinaryField", "TextField"))

    def test_alter(self):
        """
        Tests simple altering of fields
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure the field is right to begin with
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "CharField")
        self.assertEqual(bool(columns['name'][1][6]), bool(connection.features.interprets_empty_strings_as_nulls))
        # Alter the name field to a TextField
        old_field = Author._meta.get_field("name")
        new_field = TextField(null=True)
        new_field.set_attributes_from_name("name")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "TextField")
        self.assertEqual(columns['name'][1][6], True)
        # Change nullability again
        new_field2 = TextField(null=False)
        new_field2.set_attributes_from_name("name")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, new_field, new_field2, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "TextField")
        self.assertEqual(bool(columns['name'][1][6]), bool(connection.features.interprets_empty_strings_as_nulls))

    def test_alter_text_field(self):
        # Regression for "BLOB/TEXT column 'info' can't have a default value")
        # on MySQL.
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Note)
        old_field = Note._meta.get_field("info")
        new_field = TextField(blank=True)
        new_field.set_attributes_from_name("info")
        with connection.schema_editor() as editor:
            editor.alter_field(Note, old_field, new_field, strict=True)

    @skipIfDBFeature('interprets_empty_strings_as_nulls')
    def test_alter_textual_field_keep_null_status(self):
        """
        Changing a field type shouldn't affect the not null status.
        """
        with connection.schema_editor() as editor:
            editor.create_model(Note)
        with self.assertRaises(IntegrityError):
            Note.objects.create(info=None)
        old_field = Note._meta.get_field("info")
        new_field = CharField(max_length=50)
        new_field.set_attributes_from_name("info")
        with connection.schema_editor() as editor:
            editor.alter_field(Note, old_field, new_field, strict=True)
        with self.assertRaises(IntegrityError):
            Note.objects.create(info=None)

    def test_alter_numeric_field_keep_null_status(self):
        """
        Changing a field type shouldn't affect the not null status.
        """
        with connection.schema_editor() as editor:
            editor.create_model(UniqueTest)
        with self.assertRaises(IntegrityError):
            UniqueTest.objects.create(year=None, slug='aaa')
        old_field = UniqueTest._meta.get_field("year")
        new_field = BigIntegerField()
        new_field.set_attributes_from_name("year")
        with connection.schema_editor() as editor:
            editor.alter_field(UniqueTest, old_field, new_field, strict=True)
        with self.assertRaises(IntegrityError):
            UniqueTest.objects.create(year=None, slug='bbb')

    def test_alter_null_to_not_null(self):
        """
        #23609 - Tests handling of default values when altering from NULL to NOT NULL.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure the field is right to begin with
        columns = self.column_classes(Author)
        self.assertTrue(columns['height'][1][6])
        # Create some test data
        Author.objects.create(name='Not null author', height=12)
        Author.objects.create(name='Null author')
        # Verify null value
        self.assertEqual(Author.objects.get(name='Not null author').height, 12)
        self.assertIsNone(Author.objects.get(name='Null author').height)
        # Alter the height field to NOT NULL with default
        old_field = Author._meta.get_field("height")
        new_field = PositiveIntegerField(default=42)
        new_field.set_attributes_from_name("height")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertFalse(columns['height'][1][6])
        # Verify default value
        self.assertEqual(Author.objects.get(name='Not null author').height, 12)
        self.assertEqual(Author.objects.get(name='Null author').height, 42)

    def test_alter_charfield_to_null(self):
        """
        #24307 - Should skip an alter statement on databases with
        interprets_empty_strings_as_null when changing a CharField to null.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Change the CharField to null
        old_field = Author._meta.get_field('name')
        new_field = copy(old_field)
        new_field.null = True
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field)

    def test_alter_textfield_to_null(self):
        """
        #24307 - Should skip an alter statement on databases with
        interprets_empty_strings_as_null when changing a TextField to null.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Note)
        # Change the TextField to null
        old_field = Note._meta.get_field('info')
        new_field = copy(old_field)
        new_field.null = True
        with connection.schema_editor() as editor:
            editor.alter_field(Note, old_field, new_field)

    @unittest.skipUnless(connection.features.supports_combined_alters, "No combined ALTER support")
    def test_alter_null_to_not_null_keeping_default(self):
        """
        #23738 - Can change a nullable field with default to non-nullable
        with the same default.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(AuthorWithDefaultHeight)
        # Ensure the field is right to begin with
        columns = self.column_classes(AuthorWithDefaultHeight)
        self.assertTrue(columns['height'][1][6])
        # Alter the height field to NOT NULL keeping the previous default
        old_field = AuthorWithDefaultHeight._meta.get_field("height")
        new_field = PositiveIntegerField(default=42)
        new_field.set_attributes_from_name("height")
        with connection.schema_editor() as editor:
            editor.alter_field(AuthorWithDefaultHeight, old_field, new_field)
        # Ensure the field is right afterwards
        columns = self.column_classes(AuthorWithDefaultHeight)
        self.assertFalse(columns['height'][1][6])

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_alter_fk(self):
        """
        Tests altering of FKs
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(Book)
        # Ensure the field is right to begin with
        columns = self.column_classes(Book)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Make sure the FK constraint is present
        constraints = self.get_constraints(Book._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["author_id"] and details['foreign_key']:
                self.assertEqual(details['foreign_key'], ('schema_author', 'id'))
                break
        else:
            self.fail("No FK constraint for author_id found")
        # Alter the FK
        old_field = Book._meta.get_field("author")
        new_field = ForeignKey(Author, editable=False)
        new_field.set_attributes_from_name("author")
        with connection.schema_editor() as editor:
            editor.alter_field(Book, old_field, new_field, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(Book)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Make sure the FK constraint is present
        constraints = self.get_constraints(Book._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["author_id"] and details['foreign_key']:
                self.assertEqual(details['foreign_key'], ('schema_author', 'id'))
                break
        else:
            self.fail("No FK constraint for author_id found")

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_alter_to_fk(self):
        """
        #24447 - Tests adding a FK constraint for an existing column
        """
        class LocalBook(Model):
            author = IntegerField()
            title = CharField(max_length=100, db_index=True)
            pub_date = DateTimeField()

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [LocalBook]

        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(LocalBook)
        # Ensure no FK constraint exists
        constraints = self.get_constraints(LocalBook._meta.db_table)
        for name, details in constraints.items():
            if details['foreign_key']:
                self.fail('Found an unexpected FK constraint to %s' % details['columns'])
        old_field = LocalBook._meta.get_field("author")
        new_field = ForeignKey(Author)
        new_field.set_attributes_from_name("author")
        with connection.schema_editor() as editor:
            editor.alter_field(LocalBook, old_field, new_field, strict=True)
        constraints = self.get_constraints(LocalBook._meta.db_table)
        # Ensure FK constraint exists
        for name, details in constraints.items():
            if details['foreign_key'] and details['columns'] == ["author_id"]:
                self.assertEqual(details['foreign_key'], ('schema_author', 'id'))
                break
        else:
            self.fail("No FK constraint for author_id found")

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_alter_o2o_to_fk(self):
        """
        #24163 - Tests altering of OneToOneField to ForeignKey
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(BookWithO2O)
        # Ensure the field is right to begin with
        columns = self.column_classes(BookWithO2O)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Ensure the field is unique
        author = Author.objects.create(name="Joe")
        BookWithO2O.objects.create(author=author, title="Django 1", pub_date=datetime.datetime.now())
        with self.assertRaises(IntegrityError):
            BookWithO2O.objects.create(author=author, title="Django 2", pub_date=datetime.datetime.now())
        BookWithO2O.objects.all().delete()
        # Make sure the FK constraint is present
        constraints = self.get_constraints(BookWithO2O._meta.db_table)
        author_is_fk = False
        for name, details in constraints.items():
            if details['columns'] == ['author_id']:
                if details['foreign_key'] and details['foreign_key'] == ('schema_author', 'id'):
                    author_is_fk = True
        self.assertTrue(author_is_fk, "No FK constraint for author_id found")
        # Alter the OneToOneField to ForeignKey
        old_field = BookWithO2O._meta.get_field("author")
        new_field = ForeignKey(Author)
        new_field.set_attributes_from_name("author")
        with connection.schema_editor() as editor:
            editor.alter_field(BookWithO2O, old_field, new_field, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(Book)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Ensure the field is not unique anymore
        Book.objects.create(author=author, title="Django 1", pub_date=datetime.datetime.now())
        Book.objects.create(author=author, title="Django 2", pub_date=datetime.datetime.now())
        # Make sure the FK constraint is still present
        constraints = self.get_constraints(Book._meta.db_table)
        author_is_fk = False
        for name, details in constraints.items():
            if details['columns'] == ['author_id']:
                if details['foreign_key'] and details['foreign_key'] == ('schema_author', 'id'):
                    author_is_fk = True
        self.assertTrue(author_is_fk, "No FK constraint for author_id found")

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_alter_fk_to_o2o(self):
        """
        #24163 - Tests altering of ForeignKey to OneToOneField
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(Book)
        # Ensure the field is right to begin with
        columns = self.column_classes(Book)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Ensure the field is not unique
        author = Author.objects.create(name="Joe")
        Book.objects.create(author=author, title="Django 1", pub_date=datetime.datetime.now())
        Book.objects.create(author=author, title="Django 2", pub_date=datetime.datetime.now())
        Book.objects.all().delete()
        # Make sure the FK constraint is present
        constraints = self.get_constraints(Book._meta.db_table)
        author_is_fk = False
        for name, details in constraints.items():
            if details['columns'] == ['author_id']:
                if details['foreign_key'] and details['foreign_key'] == ('schema_author', 'id'):
                    author_is_fk = True
        self.assertTrue(author_is_fk, "No FK constraint for author_id found")
        # Alter the ForeignKey to OneToOneField
        old_field = Book._meta.get_field("author")
        new_field = OneToOneField(Author)
        new_field.set_attributes_from_name("author")
        with connection.schema_editor() as editor:
            editor.alter_field(Book, old_field, new_field, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(BookWithO2O)
        self.assertEqual(columns['author_id'][0], "IntegerField")
        # Ensure the field is unique now
        BookWithO2O.objects.create(author=author, title="Django 1", pub_date=datetime.datetime.now())
        with self.assertRaises(IntegrityError):
            BookWithO2O.objects.create(author=author, title="Django 2", pub_date=datetime.datetime.now())
        # Make sure the FK constraint is present
        constraints = self.get_constraints(BookWithO2O._meta.db_table)
        author_is_fk = False
        for name, details in constraints.items():
            if details['columns'] == ['author_id']:
                if details['foreign_key'] and details['foreign_key'] == ('schema_author', 'id'):
                    author_is_fk = True
        self.assertTrue(author_is_fk, "No FK constraint for author_id found")

    def test_alter_implicit_id_to_explicit(self):
        """
        Should be able to convert an implicit "id" field to an explicit "id"
        primary key field.
        """
        with connection.schema_editor() as editor:
            editor.create_model(Author)

        old_field = Author._meta.get_field("id")
        new_field = IntegerField(primary_key=True)
        new_field.set_attributes_from_name("id")
        new_field.model = Author
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field, strict=True)
        # This will fail if DROP DEFAULT is inadvertently executed on this
        # field which drops the id sequence, at least on PostgreSQL.
        Author.objects.create(name='Foo')

    def test_rename(self):
        """
        Tests simple altering of fields
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure the field is right to begin with
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "CharField")
        self.assertNotIn("display_name", columns)
        # Alter the name field's name
        old_field = Author._meta.get_field("name")
        new_field = CharField(max_length=254)
        new_field.set_attributes_from_name("display_name")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field, strict=True)
        # Ensure the field is right afterwards
        columns = self.column_classes(Author)
        self.assertEqual(columns['display_name'][0], "CharField")
        self.assertNotIn("name", columns)

    def _test_m2m_create(self, M2MFieldClass):
        """
        Tests M2M fields on models during creation
        """
        class LocalBookWithM2M(Model):
            author = ForeignKey(Author)
            title = CharField(max_length=100, db_index=True)
            pub_date = DateTimeField()
            tags = M2MFieldClass("TagM2MTest", related_name="books")

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [
            LocalBookWithM2M,
            LocalBookWithM2M._meta.get_field('tags').rel.through,
        ]
        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(TagM2MTest)
            editor.create_model(LocalBookWithM2M)
        # Ensure there is now an m2m table there
        columns = self.column_classes(LocalBookWithM2M._meta.get_field("tags").rel.through)
        self.assertEqual(columns['tagm2mtest_id'][0], "IntegerField")

    def test_m2m_create(self):
        self._test_m2m_create(ManyToManyField)

    def test_m2m_create_custom(self):
        self._test_m2m_create(CustomManyToManyField)

    def test_m2m_create_inherited(self):
        self._test_m2m_create(InheritedManyToManyField)

    def _test_m2m_create_through(self, M2MFieldClass):
        """
        Tests M2M fields on models during creation with through models
        """
        class LocalTagThrough(Model):
            book = ForeignKey("schema.LocalBookWithM2MThrough")
            tag = ForeignKey("schema.TagM2MTest")

            class Meta:
                app_label = 'schema'
                apps = new_apps

        class LocalBookWithM2MThrough(Model):
            tags = M2MFieldClass("TagM2MTest", related_name="books", through=LocalTagThrough)

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [LocalTagThrough, LocalBookWithM2MThrough]

        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(LocalTagThrough)
            editor.create_model(TagM2MTest)
            editor.create_model(LocalBookWithM2MThrough)
        # Ensure there is now an m2m table there
        columns = self.column_classes(LocalTagThrough)
        self.assertEqual(columns['book_id'][0], "IntegerField")
        self.assertEqual(columns['tag_id'][0], "IntegerField")

    def test_m2m_create_through(self):
        self._test_m2m_create_through(ManyToManyField)

    def test_m2m_create_through_custom(self):
        self._test_m2m_create_through(CustomManyToManyField)

    def test_m2m_create_through_inherited(self):
        self._test_m2m_create_through(InheritedManyToManyField)

    def _test_m2m(self, M2MFieldClass):
        """
        Tests adding/removing M2M fields on models
        """
        class LocalAuthorWithM2M(Model):
            name = CharField(max_length=255)

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [LocalAuthorWithM2M]

        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(LocalAuthorWithM2M)
            editor.create_model(TagM2MTest)
        # Create an M2M field
        new_field = M2MFieldClass("schema.TagM2MTest", related_name="authors")
        new_field.contribute_to_class(LocalAuthorWithM2M, "tags")
        self.local_models += [new_field.rel.through]
        # Ensure there's no m2m table there
        self.assertRaises(DatabaseError, self.column_classes, new_field.rel.through)
        # Add the field
        with connection.schema_editor() as editor:
            editor.add_field(LocalAuthorWithM2M, new_field)
        # Ensure there is now an m2m table there
        columns = self.column_classes(new_field.rel.through)
        self.assertEqual(columns['tagm2mtest_id'][0], "IntegerField")

        # "Alter" the field. This should not rename the DB table to itself.
        with connection.schema_editor() as editor:
            editor.alter_field(LocalAuthorWithM2M, new_field, new_field)

        # Remove the M2M table again
        with connection.schema_editor() as editor:
            editor.remove_field(LocalAuthorWithM2M, new_field)
        # Ensure there's no m2m table there
        self.assertRaises(DatabaseError, self.column_classes, new_field.rel.through)

    def test_m2m(self):
        self._test_m2m(ManyToManyField)

    def test_m2m_custom(self):
        self._test_m2m(CustomManyToManyField)

    def test_m2m_inherited(self):
        self._test_m2m(InheritedManyToManyField)

    def _test_m2m_through_alter(self, M2MFieldClass):
        """
        Tests altering M2Ms with explicit through models (should no-op)
        """
        class LocalAuthorTag(Model):
            author = ForeignKey("schema.LocalAuthorWithM2MThrough")
            tag = ForeignKey("schema.TagM2MTest")

            class Meta:
                app_label = 'schema'
                apps = new_apps

        class LocalAuthorWithM2MThrough(Model):
            name = CharField(max_length=255)
            tags = M2MFieldClass("schema.TagM2MTest", related_name="authors", through=LocalAuthorTag)

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [LocalAuthorTag, LocalAuthorWithM2MThrough]

        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(LocalAuthorTag)
            editor.create_model(LocalAuthorWithM2MThrough)
            editor.create_model(TagM2MTest)
        # Ensure the m2m table is there
        self.assertEqual(len(self.column_classes(LocalAuthorTag)), 3)
        # "Alter" the field's blankness. This should not actually do anything.
        old_field = LocalAuthorWithM2MThrough._meta.get_field("tags")
        new_field = M2MFieldClass("schema.TagM2MTest", related_name="authors", through=LocalAuthorTag)
        new_field.contribute_to_class(LocalAuthorWithM2MThrough, "tags")
        with connection.schema_editor() as editor:
            editor.alter_field(LocalAuthorWithM2MThrough, old_field, new_field)
        # Ensure the m2m table is still there
        self.assertEqual(len(self.column_classes(LocalAuthorTag)), 3)

    def test_m2m_through_alter(self):
        self._test_m2m_through_alter(ManyToManyField)

    def test_m2m_through_alter_custom(self):
        self._test_m2m_through_alter(CustomManyToManyField)

    def test_m2m_through_alter_inherited(self):
        self._test_m2m_through_alter(InheritedManyToManyField)

    def _test_m2m_repoint(self, M2MFieldClass):
        """
        Tests repointing M2M fields
        """
        class LocalBookWithM2M(Model):
            author = ForeignKey(Author)
            title = CharField(max_length=100, db_index=True)
            pub_date = DateTimeField()
            tags = M2MFieldClass("TagM2MTest", related_name="books")

            class Meta:
                app_label = 'schema'
                apps = new_apps

        self.local_models = [
            LocalBookWithM2M,
            LocalBookWithM2M._meta.get_field('tags').rel.through,
        ]

        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(LocalBookWithM2M)
            editor.create_model(TagM2MTest)
            editor.create_model(UniqueTest)
        # Ensure the M2M exists and points to TagM2MTest
        constraints = self.get_constraints(LocalBookWithM2M._meta.get_field("tags").rel.through._meta.db_table)
        if connection.features.supports_foreign_keys:
            for name, details in constraints.items():
                if details['columns'] == ["tagm2mtest_id"] and details['foreign_key']:
                    self.assertEqual(details['foreign_key'], ('schema_tagm2mtest', 'id'))
                    break
            else:
                self.fail("No FK constraint for tagm2mtest_id found")
        # Repoint the M2M
        old_field = LocalBookWithM2M._meta.get_field("tags")
        new_field = M2MFieldClass(UniqueTest)
        new_field.contribute_to_class(LocalBookWithM2M, "uniques")
        self.local_models += [new_field.rel.through]
        with connection.schema_editor() as editor:
            editor.alter_field(LocalBookWithM2M, old_field, new_field)
        # Ensure old M2M is gone
        self.assertRaises(DatabaseError, self.column_classes, LocalBookWithM2M._meta.get_field("tags").rel.through)
        # Ensure the new M2M exists and points to UniqueTest
        constraints = self.get_constraints(new_field.rel.through._meta.db_table)
        if connection.features.supports_foreign_keys:
            for name, details in constraints.items():
                if details['columns'] == ["uniquetest_id"] and details['foreign_key']:
                    self.assertEqual(details['foreign_key'], ('schema_uniquetest', 'id'))
                    break
            else:
                self.fail("No FK constraint for uniquetest_id found")

    def test_m2m_repoint(self):
        self._test_m2m_repoint(ManyToManyField)

    def test_m2m_repoint_custom(self):
        self._test_m2m_repoint(CustomManyToManyField)

    def test_m2m_repoint_inherited(self):
        self._test_m2m_repoint(InheritedManyToManyField)

    @unittest.skipUnless(connection.features.supports_column_check_constraints, "No check constraints")
    def test_check_constraints(self):
        """
        Tests creating/deleting CHECK constraints
        """
        # Create the tables
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure the constraint exists
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["height"] and details['check']:
                break
        else:
            self.fail("No check constraint for height found")
        # Alter the column to remove it
        old_field = Author._meta.get_field("height")
        new_field = IntegerField(null=True, blank=True)
        new_field.set_attributes_from_name("height")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, old_field, new_field, strict=True)
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["height"] and details['check']:
                self.fail("Check constraint for height found")
        # Alter the column to re-add it
        new_field2 = Author._meta.get_field("height")
        with connection.schema_editor() as editor:
            editor.alter_field(Author, new_field, new_field2, strict=True)
        constraints = self.get_constraints(Author._meta.db_table)
        for name, details in constraints.items():
            if details['columns'] == ["height"] and details['check']:
                break
        else:
            self.fail("No check constraint for height found")

    def test_unique(self):
        """
        Tests removing and adding unique constraints to a single column.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Tag)
        # Ensure the field is unique to begin with
        Tag.objects.create(title="foo", slug="foo")
        self.assertRaises(IntegrityError, Tag.objects.create, title="bar", slug="foo")
        Tag.objects.all().delete()
        # Alter the slug field to be non-unique
        old_field = Tag._meta.get_field("slug")
        new_field = SlugField(unique=False)
        new_field.set_attributes_from_name("slug")
        with connection.schema_editor() as editor:
            editor.alter_field(Tag, old_field, new_field, strict=True)
        # Ensure the field is no longer unique
        Tag.objects.create(title="foo", slug="foo")
        Tag.objects.create(title="bar", slug="foo")
        Tag.objects.all().delete()
        # Alter the slug field to be unique
        new_field2 = SlugField(unique=True)
        new_field2.set_attributes_from_name("slug")
        with connection.schema_editor() as editor:
            editor.alter_field(Tag, new_field, new_field2, strict=True)
        # Ensure the field is unique again
        Tag.objects.create(title="foo", slug="foo")
        self.assertRaises(IntegrityError, Tag.objects.create, title="bar", slug="foo")
        Tag.objects.all().delete()
        # Rename the field
        new_field3 = SlugField(unique=True)
        new_field3.set_attributes_from_name("slug2")
        with connection.schema_editor() as editor:
            editor.alter_field(Tag, new_field2, new_field3, strict=True)
        # Ensure the field is still unique
        TagUniqueRename.objects.create(title="foo", slug2="foo")
        self.assertRaises(IntegrityError, TagUniqueRename.objects.create, title="bar", slug2="foo")
        Tag.objects.all().delete()

    def test_unique_together(self):
        """
        Tests removing and adding unique_together constraints on a model.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(UniqueTest)
        # Ensure the fields are unique to begin with
        UniqueTest.objects.create(year=2012, slug="foo")
        UniqueTest.objects.create(year=2011, slug="foo")
        UniqueTest.objects.create(year=2011, slug="bar")
        self.assertRaises(IntegrityError, UniqueTest.objects.create, year=2012, slug="foo")
        UniqueTest.objects.all().delete()
        # Alter the model to its non-unique-together companion
        with connection.schema_editor() as editor:
            editor.alter_unique_together(UniqueTest, UniqueTest._meta.unique_together, [])
        # Ensure the fields are no longer unique
        UniqueTest.objects.create(year=2012, slug="foo")
        UniqueTest.objects.create(year=2012, slug="foo")
        UniqueTest.objects.all().delete()
        # Alter it back
        new_field2 = SlugField(unique=True)
        new_field2.set_attributes_from_name("slug")
        with connection.schema_editor() as editor:
            editor.alter_unique_together(UniqueTest, [], UniqueTest._meta.unique_together)
        # Ensure the fields are unique again
        UniqueTest.objects.create(year=2012, slug="foo")
        self.assertRaises(IntegrityError, UniqueTest.objects.create, year=2012, slug="foo")
        UniqueTest.objects.all().delete()

    def test_unique_together_with_fk(self):
        """
        Tests removing and adding unique_together constraints that include
        a foreign key.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(Book)
        # Ensure the fields are unique to begin with
        self.assertEqual(Book._meta.unique_together, ())
        # Add the unique_together constraint
        with connection.schema_editor() as editor:
            editor.alter_unique_together(Book, [], [['author', 'title']])
        # Alter it back
        with connection.schema_editor() as editor:
            editor.alter_unique_together(Book, [['author', 'title']], [])

    def test_index_together(self):
        """
        Tests removing and adding index_together constraints on a model.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Tag)
        # Ensure there's no index on the year/slug columns first
        self.assertEqual(
            False,
            any(
                c["index"]
                for c in self.get_constraints("schema_tag").values()
                if c['columns'] == ["slug", "title"]
            ),
        )
        # Alter the model to add an index
        with connection.schema_editor() as editor:
            editor.alter_index_together(Tag, [], [("slug", "title")])
        # Ensure there is now an index
        self.assertEqual(
            True,
            any(
                c["index"]
                for c in self.get_constraints("schema_tag").values()
                if c['columns'] == ["slug", "title"]
            ),
        )
        # Alter it back
        new_field2 = SlugField(unique=True)
        new_field2.set_attributes_from_name("slug")
        with connection.schema_editor() as editor:
            editor.alter_index_together(Tag, [("slug", "title")], [])
        # Ensure there's no index
        self.assertEqual(
            False,
            any(
                c["index"]
                for c in self.get_constraints("schema_tag").values()
                if c['columns'] == ["slug", "title"]
            ),
        )

    def test_index_together_with_fk(self):
        """
        Tests removing and adding index_together constraints that include
        a foreign key.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(Book)
        # Ensure the fields are unique to begin with
        self.assertEqual(Book._meta.index_together, ())
        # Add the unique_together constraint
        with connection.schema_editor() as editor:
            editor.alter_index_together(Book, [], [['author', 'title']])
        # Alter it back
        with connection.schema_editor() as editor:
            editor.alter_index_together(Book, [['author', 'title']], [])

    def test_create_index_together(self):
        """
        Tests creating models with index_together already defined
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(TagIndexed)
        # Ensure there is an index
        self.assertEqual(
            True,
            any(
                c["index"]
                for c in self.get_constraints("schema_tagindexed").values()
                if c['columns'] == ["slug", "title"]
            ),
        )

    def test_db_table(self):
        """
        Tests renaming of the table
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure the table is there to begin with
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "CharField")
        # Alter the table
        with connection.schema_editor() as editor:
            editor.alter_db_table(Author, "schema_author", "schema_otherauthor")
        # Ensure the table is there afterwards
        Author._meta.db_table = "schema_otherauthor"
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "CharField")
        # Alter the table again
        with connection.schema_editor() as editor:
            editor.alter_db_table(Author, "schema_otherauthor", "schema_author")
        # Ensure the table is still there
        Author._meta.db_table = "schema_author"
        columns = self.column_classes(Author)
        self.assertEqual(columns['name'][0], "CharField")

    def test_indexes(self):
        """
        Tests creation/altering of indexes
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
            editor.create_model(Book)
        # Ensure the table is there and has the right index
        self.assertIn(
            "title",
            self.get_indexes(Book._meta.db_table),
        )
        # Alter to remove the index
        old_field = Book._meta.get_field("title")
        new_field = CharField(max_length=100, db_index=False)
        new_field.set_attributes_from_name("title")
        with connection.schema_editor() as editor:
            editor.alter_field(Book, old_field, new_field, strict=True)
        # Ensure the table is there and has no index
        self.assertNotIn(
            "title",
            self.get_indexes(Book._meta.db_table),
        )
        # Alter to re-add the index
        new_field2 = Book._meta.get_field("title")
        with connection.schema_editor() as editor:
            editor.alter_field(Book, new_field, new_field2, strict=True)
        # Ensure the table is there and has the index again
        self.assertIn(
            "title",
            self.get_indexes(Book._meta.db_table),
        )
        # Add a unique column, verify that creates an implicit index
        new_field3 = BookWithSlug._meta.get_field("slug")
        with connection.schema_editor() as editor:
            editor.add_field(Book, new_field3)
        self.assertIn(
            "slug",
            self.get_indexes(Book._meta.db_table),
        )
        # Remove the unique, check the index goes with it
        new_field4 = CharField(max_length=20, unique=False)
        new_field4.set_attributes_from_name("slug")
        with connection.schema_editor() as editor:
            editor.alter_field(BookWithSlug, new_field3, new_field4, strict=True)
        self.assertNotIn(
            "slug",
            self.get_indexes(Book._meta.db_table),
        )

    def test_primary_key(self):
        """
        Tests altering of the primary key
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Tag)
        # Ensure the table is there and has the right PK
        self.assertTrue(
            self.get_indexes(Tag._meta.db_table)['id']['primary_key'],
        )
        # Alter to change the PK
        id_field = Tag._meta.get_field("id")
        old_field = Tag._meta.get_field("slug")
        new_field = SlugField(primary_key=True)
        new_field.set_attributes_from_name("slug")
        new_field.model = Tag
        with connection.schema_editor() as editor:
            editor.remove_field(Tag, id_field)
            editor.alter_field(Tag, old_field, new_field)
        # Ensure the PK changed
        self.assertNotIn(
            'id',
            self.get_indexes(Tag._meta.db_table),
        )
        self.assertTrue(
            self.get_indexes(Tag._meta.db_table)['slug']['primary_key'],
        )

    def test_context_manager_exit(self):
        """
        Ensures transaction is correctly closed when an error occurs
        inside a SchemaEditor context.
        """
        class SomeError(Exception):
            pass
        try:
            with connection.schema_editor():
                raise SomeError
        except SomeError:
            self.assertFalse(connection.in_atomic_block)

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_foreign_key_index_long_names_regression(self):
        """
        Regression test for #21497.
        Only affects databases that supports foreign keys.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(AuthorWithEvenLongerName)
            editor.create_model(BookWithLongName)
        # Find the properly shortened column name
        column_name = connection.ops.quote_name("author_foreign_key_with_really_long_field_name_id")
        column_name = column_name[1:-1].lower()  # unquote, and, for Oracle, un-upcase
        # Ensure the table is there and has an index on the column
        self.assertIn(
            column_name,
            self.get_indexes(BookWithLongName._meta.db_table),
        )

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_add_foreign_key_long_names(self):
        """
        Regression test for #23009.
        Only affects databases that supports foreign keys.
        """
        # Create the initial tables
        with connection.schema_editor() as editor:
            editor.create_model(AuthorWithEvenLongerName)
            editor.create_model(BookWithLongName)
        # Add a second FK, this would fail due to long ref name before the fix
        new_field = ForeignKey(AuthorWithEvenLongerName, related_name="something")
        new_field.set_attributes_from_name("author_other_really_long_named_i_mean_so_long_fk")
        with connection.schema_editor() as editor:
            editor.add_field(BookWithLongName, new_field)

    def test_creation_deletion_reserved_names(self):
        """
        Tries creating a model's table, and then deleting it when it has a
        SQL reserved name.
        """
        # Create the table
        with connection.schema_editor() as editor:
            try:
                editor.create_model(Thing)
            except OperationalError as e:
                self.fail("Errors when applying initial migration for a model "
                          "with a table named after a SQL reserved word: %s" % e)
        # Check that it's there
        list(Thing.objects.all())
        # Clean up that table
        with connection.schema_editor() as editor:
            editor.delete_model(Thing)
        # Check that it's gone
        self.assertRaises(
            DatabaseError,
            lambda: list(Thing.objects.all()),
        )

    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
    def test_remove_constraints_capital_letters(self):
        """
        #23065 - Constraint names must be quoted if they contain capital letters.
        """
        def get_field(*args, **kwargs):
            kwargs['db_column'] = "CamelCase"
            field = kwargs.pop('field_class', IntegerField)(*args, **kwargs)
            field.set_attributes_from_name("CamelCase")
            return field

        model = Author
        field = get_field()
        table = model._meta.db_table
        column = field.column

        with connection.schema_editor() as editor:
            editor.create_model(model)
            editor.add_field(model, field)

            editor.execute(
                editor.sql_create_index % {
                    "table": editor.quote_name(table),
                    "name": editor.quote_name("CamelCaseIndex"),
                    "columns": editor.quote_name(column),
                    "extra": "",
                }
            )
            editor.alter_field(model, get_field(db_index=True), field)

            editor.execute(
                editor.sql_create_unique % {
                    "table": editor.quote_name(table),
                    "name": editor.quote_name("CamelCaseUniqConstraint"),
                    "columns": editor.quote_name(field.column),
                }
            )
            editor.alter_field(model, get_field(unique=True), field)

            editor.execute(
                editor.sql_create_fk % {
                    "table": editor.quote_name(table),
                    "name": editor.quote_name("CamelCaseFKConstraint"),
                    "column": editor.quote_name(column),
                    "to_table": editor.quote_name(table),
                    "to_column": editor.quote_name(model._meta.auto_field.column),
                }
            )
            editor.alter_field(model, get_field(Author, field_class=ForeignKey), field)

    def test_add_field_use_effective_default(self):
        """
        #23987 - effective_default() should be used as the field default when
        adding a new field.
        """
        # Create the table
        with connection.schema_editor() as editor:
            editor.create_model(Author)
        # Ensure there's no surname field
        columns = self.column_classes(Author)
        self.assertNotIn("surname", columns)
        # Create a row
        Author.objects.create(name='Anonymous1')
        # Add new CharField to ensure default will be used from effective_default
        new_field = CharField(max_length=15, blank=True)
        new_field.set_attributes_from_name("surname")
        with connection.schema_editor() as editor:
            editor.add_field(Author, new_field)
        # Ensure field was added with the right default
        with connection.cursor() as cursor:
            cursor.execute("SELECT surname FROM schema_author;")
            item = cursor.fetchall()[0]
            self.assertEqual(item[0], None if connection.features.interprets_empty_strings_as_nulls else '')
