before send to remote

env/lib/python3.8/site-packages/django/db/backends/mysql/base.py

@@ -0,0 +1,444 @@
+"""
+MySQL database backend for Django.
+
+Requires mysqlclient: https://pypi.org/project/mysqlclient/
+"""
+from django.core.exceptions import ImproperlyConfigured
+from django.db import IntegrityError
+from django.db.backends import utils as backend_utils
+from django.db.backends.base.base import BaseDatabaseWrapper
+from django.utils.asyncio import async_unsafe
+from django.utils.functional import cached_property
+from django.utils.regex_helper import _lazy_re_compile
+
+try:
+    import MySQLdb as Database
+except ImportError as err:
+    raise ImproperlyConfigured(
+        "Error loading MySQLdb module.\nDid you install mysqlclient?"
+    ) from err
+
+from MySQLdb.constants import CLIENT, FIELD_TYPE
+from MySQLdb.converters import conversions
+
+# Some of these import MySQLdb, so import them after checking if it's installed.
+from .client import DatabaseClient
+from .creation import DatabaseCreation
+from .features import DatabaseFeatures
+from .introspection import DatabaseIntrospection
+from .operations import DatabaseOperations
+from .schema import DatabaseSchemaEditor
+from .validation import DatabaseValidation
+
+version = Database.version_info
+if version < (1, 4, 0):
+    raise ImproperlyConfigured(
+        "mysqlclient 1.4.0 or newer is required; you have %s." % Database.__version__
+    )
+
+
+# MySQLdb returns TIME columns as timedelta -- they are more like timedelta in
+# terms of actual behavior as they are signed and include days -- and Django
+# expects time.
+django_conversions = {
+    **conversions,
+    **{FIELD_TYPE.TIME: backend_utils.typecast_time},
+}
+
+# This should match the numerical portion of the version numbers (we can treat
+# versions like 5.0.24 and 5.0.24a as the same).
+server_version_re = _lazy_re_compile(r"(\d{1,2})\.(\d{1,2})\.(\d{1,2})")
+
+
+class CursorWrapper:
+    """
+    A thin wrapper around MySQLdb's normal cursor class that catches particular
+    exception instances and reraises them with the correct types.
+
+    Implemented as a wrapper, rather than a subclass, so that it isn't stuck
+    to the particular underlying representation returned by Connection.cursor().
+    """
+
+    codes_for_integrityerror = (
+        1048,  # Column cannot be null
+        1690,  # BIGINT UNSIGNED value is out of range
+        3819,  # CHECK constraint is violated
+        4025,  # CHECK constraint failed
+    )
+
+    def __init__(self, cursor):
+        self.cursor = cursor
+
+    def execute(self, query, args=None):
+        try:
+            # args is None means no string interpolation
+            return self.cursor.execute(query, args)
+        except Database.OperationalError as e:
+            # Map some error codes to IntegrityError, since they seem to be
+            # misclassified and Django would prefer the more logical place.
+            if e.args[0] in self.codes_for_integrityerror:
+                raise IntegrityError(*tuple(e.args))
+            raise
+
+    def executemany(self, query, args):
+        try:
+            return self.cursor.executemany(query, args)
+        except Database.OperationalError as e:
+            # Map some error codes to IntegrityError, since they seem to be
+            # misclassified and Django would prefer the more logical place.
+            if e.args[0] in self.codes_for_integrityerror:
+                raise IntegrityError(*tuple(e.args))
+            raise
+
+    def __getattr__(self, attr):
+        return getattr(self.cursor, attr)
+
+    def __iter__(self):
+        return iter(self.cursor)
+
+
+class DatabaseWrapper(BaseDatabaseWrapper):
+    vendor = "mysql"
+    # This dictionary maps Field objects to their associated MySQL column
+    # types, as strings. Column-type strings can contain format strings; they'll
+    # be interpolated against the values of Field.__dict__ before being output.
+    # If a column type is set to None, it won't be included in the output.
+    data_types = {
+        "AutoField": "integer AUTO_INCREMENT",
+        "BigAutoField": "bigint AUTO_INCREMENT",
+        "BinaryField": "longblob",
+        "BooleanField": "bool",
+        "CharField": "varchar(%(max_length)s)",
+        "DateField": "date",
+        "DateTimeField": "datetime(6)",
+        "DecimalField": "numeric(%(max_digits)s, %(decimal_places)s)",
+        "DurationField": "bigint",
+        "FileField": "varchar(%(max_length)s)",
+        "FilePathField": "varchar(%(max_length)s)",
+        "FloatField": "double precision",
+        "IntegerField": "integer",
+        "BigIntegerField": "bigint",
+        "IPAddressField": "char(15)",
+        "GenericIPAddressField": "char(39)",
+        "JSONField": "json",
+        "OneToOneField": "integer",
+        "PositiveBigIntegerField": "bigint UNSIGNED",
+        "PositiveIntegerField": "integer UNSIGNED",
+        "PositiveSmallIntegerField": "smallint UNSIGNED",
+        "SlugField": "varchar(%(max_length)s)",
+        "SmallAutoField": "smallint AUTO_INCREMENT",
+        "SmallIntegerField": "smallint",
+        "TextField": "longtext",
+        "TimeField": "time(6)",
+        "UUIDField": "char(32)",
+    }
+
+    # For these data types:
+    # - MySQL < 8.0.13 doesn't accept default values and implicitly treats them
+    #   as nullable
+    # - all versions of MySQL and MariaDB don't support full width database
+    #   indexes
+    _limited_data_types = (
+        "tinyblob",
+        "blob",
+        "mediumblob",
+        "longblob",
+        "tinytext",
+        "text",
+        "mediumtext",
+        "longtext",
+        "json",
+    )
+
+    operators = {
+        "exact": "= %s",
+        "iexact": "LIKE %s",
+        "contains": "LIKE BINARY %s",
+        "icontains": "LIKE %s",
+        "gt": "> %s",
+        "gte": ">= %s",
+        "lt": "< %s",
+        "lte": "<= %s",
+        "startswith": "LIKE BINARY %s",
+        "endswith": "LIKE BINARY %s",
+        "istartswith": "LIKE %s",
+        "iendswith": "LIKE %s",
+    }
+
+    # The patterns below are used to generate SQL pattern lookup clauses when
+    # the right-hand side of the lookup isn't a raw string (it might be an expression
+    # or the result of a bilateral transformation).
+    # In those cases, special characters for LIKE operators (e.g. \, *, _) should be
+    # escaped on database side.
+    #
+    # Note: we use str.format() here for readability as '%' is used as a wildcard for
+    # the LIKE operator.
+    pattern_esc = r"REPLACE(REPLACE(REPLACE({}, '\\', '\\\\'), '%%', '\%%'), '_', '\_')"
+    pattern_ops = {
+        "contains": "LIKE BINARY CONCAT('%%', {}, '%%')",
+        "icontains": "LIKE CONCAT('%%', {}, '%%')",
+        "startswith": "LIKE BINARY CONCAT({}, '%%')",
+        "istartswith": "LIKE CONCAT({}, '%%')",
+        "endswith": "LIKE BINARY CONCAT('%%', {})",
+        "iendswith": "LIKE CONCAT('%%', {})",
+    }
+
+    isolation_levels = {
+        "read uncommitted",
+        "read committed",
+        "repeatable read",
+        "serializable",
+    }
+
+    Database = Database
+    SchemaEditorClass = DatabaseSchemaEditor
+    # Classes instantiated in __init__().
+    client_class = DatabaseClient
+    creation_class = DatabaseCreation
+    features_class = DatabaseFeatures
+    introspection_class = DatabaseIntrospection
+    ops_class = DatabaseOperations
+    validation_class = DatabaseValidation
+
+    def get_database_version(self):
+        return self.mysql_version
+
+    def get_connection_params(self):
+        kwargs = {
+            "conv": django_conversions,
+            "charset": "utf8",
+        }
+        settings_dict = self.settings_dict
+        if settings_dict["USER"]:
+            kwargs["user"] = settings_dict["USER"]
+        if settings_dict["NAME"]:
+            kwargs["database"] = settings_dict["NAME"]
+        if settings_dict["PASSWORD"]:
+            kwargs["password"] = settings_dict["PASSWORD"]
+        if settings_dict["HOST"].startswith("/"):
+            kwargs["unix_socket"] = settings_dict["HOST"]
+        elif settings_dict["HOST"]:
+            kwargs["host"] = settings_dict["HOST"]
+        if settings_dict["PORT"]:
+            kwargs["port"] = int(settings_dict["PORT"])
+        # We need the number of potentially affected rows after an
+        # "UPDATE", not the number of changed rows.
+        kwargs["client_flag"] = CLIENT.FOUND_ROWS
+        # Validate the transaction isolation level, if specified.
+        options = settings_dict["OPTIONS"].copy()
+        isolation_level = options.pop("isolation_level", "read committed")
+        if isolation_level:
+            isolation_level = isolation_level.lower()
+            if isolation_level not in self.isolation_levels:
+                raise ImproperlyConfigured(
+                    "Invalid transaction isolation level '%s' specified.\n"
+                    "Use one of %s, or None."
+                    % (
+                        isolation_level,
+                        ", ".join("'%s'" % s for s in sorted(self.isolation_levels)),
+                    )
+                )
+        self.isolation_level = isolation_level
+        kwargs.update(options)
+        return kwargs
+
+    @async_unsafe
+    def get_new_connection(self, conn_params):
+        connection = Database.connect(**conn_params)
+        # bytes encoder in mysqlclient doesn't work and was added only to
+        # prevent KeyErrors in Django < 2.0. We can remove this workaround when
+        # mysqlclient 2.1 becomes the minimal mysqlclient supported by Django.
+        # See https://github.com/PyMySQL/mysqlclient/issues/489
+        if connection.encoders.get(bytes) is bytes:
+            connection.encoders.pop(bytes)
+        return connection
+
+    def init_connection_state(self):
+        super().init_connection_state()
+        assignments = []
+        if self.features.is_sql_auto_is_null_enabled:
+            # SQL_AUTO_IS_NULL controls whether an AUTO_INCREMENT column on
+            # a recently inserted row will return when the field is tested
+            # for NULL. Disabling this brings this aspect of MySQL in line
+            # with SQL standards.
+            assignments.append("SET SQL_AUTO_IS_NULL = 0")
+
+        if self.isolation_level:
+            assignments.append(
+                "SET SESSION TRANSACTION ISOLATION LEVEL %s"
+                % self.isolation_level.upper()
+            )
+
+        if assignments:
+            with self.cursor() as cursor:
+                cursor.execute("; ".join(assignments))
+
+    @async_unsafe
+    def create_cursor(self, name=None):
+        cursor = self.connection.cursor()
+        return CursorWrapper(cursor)
+
+    def _rollback(self):
+        try:
+            BaseDatabaseWrapper._rollback(self)
+        except Database.NotSupportedError:
+            pass
+
+    def _set_autocommit(self, autocommit):
+        with self.wrap_database_errors:
+            self.connection.autocommit(autocommit)
+
+    def disable_constraint_checking(self):
+        """
+        Disable foreign key checks, primarily for use in adding rows with
+        forward references. Always return True to indicate constraint checks
+        need to be re-enabled.
+        """
+        with self.cursor() as cursor:
+            cursor.execute("SET foreign_key_checks=0")
+        return True
+
+    def enable_constraint_checking(self):
+        """
+        Re-enable foreign key checks after they have been disabled.
+        """
+        # Override needs_rollback in case constraint_checks_disabled is
+        # nested inside transaction.atomic.
+        self.needs_rollback, needs_rollback = False, self.needs_rollback
+        try:
+            with self.cursor() as cursor:
+                cursor.execute("SET foreign_key_checks=1")
+        finally:
+            self.needs_rollback = needs_rollback
+
+    def check_constraints(self, table_names=None):
+        """
+        Check each table name in `table_names` for rows with invalid foreign
+        key references. This method is intended to be used in conjunction with
+        `disable_constraint_checking()` and `enable_constraint_checking()`, to
+        determine if rows with invalid references were entered while constraint
+        checks were off.
+        """
+        with self.cursor() as cursor:
+            if table_names is None:
+                table_names = self.introspection.table_names(cursor)
+            for table_name in table_names:
+                primary_key_column_name = self.introspection.get_primary_key_column(
+                    cursor, table_name
+                )
+                if not primary_key_column_name:
+                    continue
+                relations = self.introspection.get_relations(cursor, table_name)
+                for column_name, (
+                    referenced_column_name,
+                    referenced_table_name,
+                ) in relations.items():
+                    cursor.execute(
+                        """
+                        SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
+                        LEFT JOIN `%s` as REFERRED
+                        ON (REFERRING.`%s` = REFERRED.`%s`)
+                        WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
+                        """
+                        % (
+                            primary_key_column_name,
+                            column_name,
+                            table_name,
+                            referenced_table_name,
+                            column_name,
+                            referenced_column_name,
+                            column_name,
+                            referenced_column_name,
+                        )
+                    )
+                    for bad_row in cursor.fetchall():
+                        raise IntegrityError(
+                            "The row in table '%s' with primary key '%s' has an "
+                            "invalid foreign key: %s.%s contains a value '%s' that "
+                            "does not have a corresponding value in %s.%s."
+                            % (
+                                table_name,
+                                bad_row[0],
+                                table_name,
+                                column_name,
+                                bad_row[1],
+                                referenced_table_name,
+                                referenced_column_name,
+                            )
+                        )
+
+    def is_usable(self):
+        try:
+            self.connection.ping()
+        except Database.Error:
+            return False
+        else:
+            return True
+
+    @cached_property
+    def display_name(self):
+        return "MariaDB" if self.mysql_is_mariadb else "MySQL"
+
+    @cached_property
+    def data_type_check_constraints(self):
+        if self.features.supports_column_check_constraints:
+            check_constraints = {
+                "PositiveBigIntegerField": "`%(column)s` >= 0",
+                "PositiveIntegerField": "`%(column)s` >= 0",
+                "PositiveSmallIntegerField": "`%(column)s` >= 0",
+            }
+            if self.mysql_is_mariadb and self.mysql_version < (10, 4, 3):
+                # MariaDB < 10.4.3 doesn't automatically use the JSON_VALID as
+                # a check constraint.
+                check_constraints["JSONField"] = "JSON_VALID(`%(column)s`)"
+            return check_constraints
+        return {}
+
+    @cached_property
+    def mysql_server_data(self):
+        with self.temporary_connection() as cursor:
+            # Select some server variables and test if the time zone
+            # definitions are installed. CONVERT_TZ returns NULL if 'UTC'
+            # timezone isn't loaded into the mysql.time_zone table.
+            cursor.execute(
+                """
+                SELECT VERSION(),
+                       @@sql_mode,
+                       @@default_storage_engine,
+                       @@sql_auto_is_null,
+                       @@lower_case_table_names,
+                       CONVERT_TZ('2001-01-01 01:00:00', 'UTC', 'UTC') IS NOT NULL
+            """
+            )
+            row = cursor.fetchone()
+        return {
+            "version": row[0],
+            "sql_mode": row[1],
+            "default_storage_engine": row[2],
+            "sql_auto_is_null": bool(row[3]),
+            "lower_case_table_names": bool(row[4]),
+            "has_zoneinfo_database": bool(row[5]),
+        }
+
+    @cached_property
+    def mysql_server_info(self):
+        return self.mysql_server_data["version"]
+
+    @cached_property
+    def mysql_version(self):
+        match = server_version_re.match(self.mysql_server_info)
+        if not match:
+            raise Exception(
+                "Unable to determine MySQL version from version string %r"
+                % self.mysql_server_info
+            )
+        return tuple(int(x) for x in match.groups())
+
+    @cached_property
+    def mysql_is_mariadb(self):
+        return "mariadb" in self.mysql_server_info.lower()
+
+    @cached_property
+    def sql_mode(self):
+        sql_mode = self.mysql_server_data["sql_mode"]
+        return set(sql_mode.split(",") if sql_mode else ())

env/lib/python3.8/site-packages/django/db/backends/mysql/client.py

@@ -0,0 +1,60 @@
+from django.db.backends.base.client import BaseDatabaseClient
+
+
+class DatabaseClient(BaseDatabaseClient):
+    executable_name = "mysql"
+
+    @classmethod
+    def settings_to_cmd_args_env(cls, settings_dict, parameters):
+        args = [cls.executable_name]
+        env = None
+        database = settings_dict["OPTIONS"].get(
+            "database",
+            settings_dict["OPTIONS"].get("db", settings_dict["NAME"]),
+        )
+        user = settings_dict["OPTIONS"].get("user", settings_dict["USER"])
+        password = settings_dict["OPTIONS"].get(
+            "password",
+            settings_dict["OPTIONS"].get("passwd", settings_dict["PASSWORD"]),
+        )
+        host = settings_dict["OPTIONS"].get("host", settings_dict["HOST"])
+        port = settings_dict["OPTIONS"].get("port", settings_dict["PORT"])
+        server_ca = settings_dict["OPTIONS"].get("ssl", {}).get("ca")
+        client_cert = settings_dict["OPTIONS"].get("ssl", {}).get("cert")
+        client_key = settings_dict["OPTIONS"].get("ssl", {}).get("key")
+        defaults_file = settings_dict["OPTIONS"].get("read_default_file")
+        charset = settings_dict["OPTIONS"].get("charset")
+        # Seems to be no good way to set sql_mode with CLI.
+
+        if defaults_file:
+            args += ["--defaults-file=%s" % defaults_file]
+        if user:
+            args += ["--user=%s" % user]
+        if password:
+            # The MYSQL_PWD environment variable usage is discouraged per
+            # MySQL's documentation due to the possibility of exposure through
+            # `ps` on old Unix flavors but --password suffers from the same
+            # flaw on even more systems. Usage of an environment variable also
+            # prevents password exposure if the subprocess.run(check=True) call
+            # raises a CalledProcessError since the string representation of
+            # the latter includes all of the provided `args`.
+            env = {"MYSQL_PWD": password}
+        if host:
+            if "/" in host:
+                args += ["--socket=%s" % host]
+            else:
+                args += ["--host=%s" % host]
+        if port:
+            args += ["--port=%s" % port]
+        if server_ca:
+            args += ["--ssl-ca=%s" % server_ca]
+        if client_cert:
+            args += ["--ssl-cert=%s" % client_cert]
+        if client_key:
+            args += ["--ssl-key=%s" % client_key]
+        if charset:
+            args += ["--default-character-set=%s" % charset]
+        if database:
+            args += [database]
+        args.extend(parameters)
+        return args, env

env/lib/python3.8/site-packages/django/db/backends/mysql/compiler.py

@@ -0,0 +1,77 @@
+from django.core.exceptions import FieldError
+from django.db.models.expressions import Col
+from django.db.models.sql import compiler
+
+
+class SQLCompiler(compiler.SQLCompiler):
+    def as_subquery_condition(self, alias, columns, compiler):
+        qn = compiler.quote_name_unless_alias
+        qn2 = self.connection.ops.quote_name
+        sql, params = self.as_sql()
+        return (
+            "(%s) IN (%s)"
+            % (
+                ", ".join("%s.%s" % (qn(alias), qn2(column)) for column in columns),
+                sql,
+            ),
+            params,
+        )
+
+
+class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
+    pass
+
+
+class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
+    def as_sql(self):
+        # Prefer the non-standard DELETE FROM syntax over the SQL generated by
+        # the SQLDeleteCompiler's default implementation when multiple tables
+        # are involved since MySQL/MariaDB will generate a more efficient query
+        # plan than when using a subquery.
+        where, having = self.query.where.split_having()
+        if self.single_alias or having:
+            # DELETE FROM cannot be used when filtering against aggregates
+            # since it doesn't allow for GROUP BY and HAVING clauses.
+            return super().as_sql()
+        result = [
+            "DELETE %s FROM"
+            % self.quote_name_unless_alias(self.query.get_initial_alias())
+        ]
+        from_sql, from_params = self.get_from_clause()
+        result.extend(from_sql)
+        where_sql, where_params = self.compile(where)
+        if where_sql:
+            result.append("WHERE %s" % where_sql)
+        return " ".join(result), tuple(from_params) + tuple(where_params)
+
+
+class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):
+    def as_sql(self):
+        update_query, update_params = super().as_sql()
+        # MySQL and MariaDB support UPDATE ... ORDER BY syntax.
+        if self.query.order_by:
+            order_by_sql = []
+            order_by_params = []
+            db_table = self.query.get_meta().db_table
+            try:
+                for resolved, (sql, params, _) in self.get_order_by():
+                    if (
+                        isinstance(resolved.expression, Col)
+                        and resolved.expression.alias != db_table
+                    ):
+                        # Ignore ordering if it contains joined fields, because
+                        # they cannot be used in the ORDER BY clause.
+                        raise FieldError
+                    order_by_sql.append(sql)
+                    order_by_params.extend(params)
+                update_query += " ORDER BY " + ", ".join(order_by_sql)
+                update_params += tuple(order_by_params)
+            except FieldError:
+                # Ignore ordering if it contains annotations, because they're
+                # removed in .update() and cannot be resolved.
+                pass
+        return update_query, update_params
+
+
+class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):
+    pass

env/lib/python3.8/site-packages/django/db/backends/mysql/creation.py

@@ -0,0 +1,87 @@
+import os
+import subprocess
+import sys
+
+from django.db.backends.base.creation import BaseDatabaseCreation
+
+from .client import DatabaseClient
+
+
+class DatabaseCreation(BaseDatabaseCreation):
+    def sql_table_creation_suffix(self):
+        suffix = []
+        test_settings = self.connection.settings_dict["TEST"]
+        if test_settings["CHARSET"]:
+            suffix.append("CHARACTER SET %s" % test_settings["CHARSET"])
+        if test_settings["COLLATION"]:
+            suffix.append("COLLATE %s" % test_settings["COLLATION"])
+        return " ".join(suffix)
+
+    def _execute_create_test_db(self, cursor, parameters, keepdb=False):
+        try:
+            super()._execute_create_test_db(cursor, parameters, keepdb)
+        except Exception as e:
+            if len(e.args) < 1 or e.args[0] != 1007:
+                # All errors except "database exists" (1007) cancel tests.
+                self.log("Got an error creating the test database: %s" % e)
+                sys.exit(2)
+            else:
+                raise
+
+    def _clone_test_db(self, suffix, verbosity, keepdb=False):
+        source_database_name = self.connection.settings_dict["NAME"]
+        target_database_name = self.get_test_db_clone_settings(suffix)["NAME"]
+        test_db_params = {
+            "dbname": self.connection.ops.quote_name(target_database_name),
+            "suffix": self.sql_table_creation_suffix(),
+        }
+        with self._nodb_cursor() as cursor:
+            try:
+                self._execute_create_test_db(cursor, test_db_params, keepdb)
+            except Exception:
+                if keepdb:
+                    # If the database should be kept, skip everything else.
+                    return
+                try:
+                    if verbosity >= 1:
+                        self.log(
+                            "Destroying old test database for alias %s..."
+                            % (
+                                self._get_database_display_str(
+                                    verbosity, target_database_name
+                                ),
+                            )
+                        )
+                    cursor.execute("DROP DATABASE %(dbname)s" % test_db_params)
+                    self._execute_create_test_db(cursor, test_db_params, keepdb)
+                except Exception as e:
+                    self.log("Got an error recreating the test database: %s" % e)
+                    sys.exit(2)
+        self._clone_db(source_database_name, target_database_name)
+
+    def _clone_db(self, source_database_name, target_database_name):
+        cmd_args, cmd_env = DatabaseClient.settings_to_cmd_args_env(
+            self.connection.settings_dict, []
+        )
+        dump_cmd = [
+            "mysqldump",
+            *cmd_args[1:-1],
+            "--routines",
+            "--events",
+            source_database_name,
+        ]
+        dump_env = load_env = {**os.environ, **cmd_env} if cmd_env else None
+        load_cmd = cmd_args
+        load_cmd[-1] = target_database_name
+
+        with subprocess.Popen(
+            dump_cmd, stdout=subprocess.PIPE, env=dump_env
+        ) as dump_proc:
+            with subprocess.Popen(
+                load_cmd,
+                stdin=dump_proc.stdout,
+                stdout=subprocess.DEVNULL,
+                env=load_env,
+            ):
+                # Allow dump_proc to receive a SIGPIPE if the load process exits.
+                dump_proc.stdout.close()

env/lib/python3.8/site-packages/django/db/backends/mysql/features.py

@@ -0,0 +1,380 @@
+import operator
+
+from django.db.backends.base.features import BaseDatabaseFeatures
+from django.utils.functional import cached_property
+
+
+class DatabaseFeatures(BaseDatabaseFeatures):
+    empty_fetchmany_value = ()
+    allows_group_by_pk = True
+    related_fields_match_type = True
+    # MySQL doesn't support sliced subqueries with IN/ALL/ANY/SOME.
+    allow_sliced_subqueries_with_in = False
+    has_select_for_update = True
+    supports_forward_references = False
+    supports_regex_backreferencing = False
+    supports_date_lookup_using_string = False
+    supports_timezones = False
+    requires_explicit_null_ordering_when_grouping = True
+    can_release_savepoints = True
+    atomic_transactions = False
+    can_clone_databases = True
+    supports_temporal_subtraction = True
+    supports_select_intersection = False
+    supports_select_difference = False
+    supports_slicing_ordering_in_compound = True
+    supports_index_on_text_field = False
+    supports_update_conflicts = True
+    create_test_procedure_without_params_sql = """
+        CREATE PROCEDURE test_procedure ()
+        BEGIN
+            DECLARE V_I INTEGER;
+            SET V_I = 1;
+        END;
+    """
+    create_test_procedure_with_int_param_sql = """
+        CREATE PROCEDURE test_procedure (P_I INTEGER)
+        BEGIN
+            DECLARE V_I INTEGER;
+            SET V_I = P_I;
+        END;
+    """
+    # Neither MySQL nor MariaDB support partial indexes.
+    supports_partial_indexes = False
+    # COLLATE must be wrapped in parentheses because MySQL treats COLLATE as an
+    # indexed expression.
+    collate_as_index_expression = True
+
+    supports_order_by_nulls_modifier = False
+    order_by_nulls_first = True
+    supports_logical_xor = True
+
+    @cached_property
+    def minimum_database_version(self):
+        if self.connection.mysql_is_mariadb:
+            return (10, 3)
+        else:
+            return (5, 7)
+
+    @cached_property
+    def bare_select_suffix(self):
+        if (
+            self.connection.mysql_is_mariadb and self.connection.mysql_version < (10, 4)
+        ) or (
+            not self.connection.mysql_is_mariadb
+            and self.connection.mysql_version < (8,)
+        ):
+            return " FROM DUAL"
+        return ""
+
+    @cached_property
+    def test_collations(self):
+        charset = "utf8"
+        if (
+            self.connection.mysql_is_mariadb
+            and self.connection.mysql_version >= (10, 6)
+        ) or (
+            not self.connection.mysql_is_mariadb
+            and self.connection.mysql_version >= (8, 0, 30)
+        ):
+            # utf8 is an alias for utf8mb3 in MariaDB 10.6+ and MySQL 8.0.30+.
+            charset = "utf8mb3"
+        return {
+            "ci": f"{charset}_general_ci",
+            "non_default": f"{charset}_esperanto_ci",
+            "swedish_ci": f"{charset}_swedish_ci",
+        }
+
+    test_now_utc_template = "UTC_TIMESTAMP"
+
+    @cached_property
+    def django_test_skips(self):
+        skips = {
+            "This doesn't work on MySQL.": {
+                "db_functions.comparison.test_greatest.GreatestTests."
+                "test_coalesce_workaround",
+                "db_functions.comparison.test_least.LeastTests."
+                "test_coalesce_workaround",
+            },
+            "Running on MySQL requires utf8mb4 encoding (#18392).": {
+                "model_fields.test_textfield.TextFieldTests.test_emoji",
+                "model_fields.test_charfield.TestCharField.test_emoji",
+            },
+            "MySQL doesn't support functional indexes on a function that "
+            "returns JSON": {
+                "schema.tests.SchemaTests.test_func_index_json_key_transform",
+            },
+            "MySQL supports multiplying and dividing DurationFields by a "
+            "scalar value but it's not implemented (#25287).": {
+                "expressions.tests.FTimeDeltaTests.test_durationfield_multiply_divide",
+            },
+            "UPDATE ... ORDER BY syntax on MySQL/MariaDB does not support ordering by"
+            "related fields.": {
+                "update.tests.AdvancedTests."
+                "test_update_ordered_by_inline_m2m_annotation",
+                "update.tests.AdvancedTests.test_update_ordered_by_m2m_annotation",
+            },
+        }
+        if "ONLY_FULL_GROUP_BY" in self.connection.sql_mode:
+            skips.update(
+                {
+                    "GROUP BY optimization does not work properly when "
+                    "ONLY_FULL_GROUP_BY mode is enabled on MySQL, see #31331.": {
+                        "aggregation.tests.AggregateTestCase."
+                        "test_aggregation_subquery_annotation_multivalued",
+                        "annotations.tests.NonAggregateAnnotationTestCase."
+                        "test_annotation_aggregate_with_m2o",
+                    },
+                }
+            )
+        if not self.connection.mysql_is_mariadb and self.connection.mysql_version < (
+            8,
+        ):
+            skips.update(
+                {
+                    "Casting to datetime/time is not supported by MySQL < 8.0. "
+                    "(#30224)": {
+                        "aggregation.tests.AggregateTestCase."
+                        "test_aggregation_default_using_time_from_python",
+                        "aggregation.tests.AggregateTestCase."
+                        "test_aggregation_default_using_datetime_from_python",
+                    },
+                    "MySQL < 8.0 returns string type instead of datetime/time. "
+                    "(#30224)": {
+                        "aggregation.tests.AggregateTestCase."
+                        "test_aggregation_default_using_time_from_database",
+                        "aggregation.tests.AggregateTestCase."
+                        "test_aggregation_default_using_datetime_from_database",
+                    },
+                }
+            )
+        if self.connection.mysql_is_mariadb and (
+            10,
+            4,
+            3,
+        ) < self.connection.mysql_version < (10, 5, 2):
+            skips.update(
+                {
+                    "https://jira.mariadb.org/browse/MDEV-19598": {
+                        "schema.tests.SchemaTests."
+                        "test_alter_not_unique_field_to_primary_key",
+                    },
+                }
+            )
+        if self.connection.mysql_is_mariadb and (
+            10,
+            4,
+            12,
+        ) < self.connection.mysql_version < (10, 5):
+            skips.update(
+                {
+                    "https://jira.mariadb.org/browse/MDEV-22775": {
+                        "schema.tests.SchemaTests."
+                        "test_alter_pk_with_self_referential_field",
+                    },
+                }
+            )
+        if (
+            self.connection.mysql_is_mariadb and self.connection.mysql_version < (10, 4)
+        ) or (
+            not self.connection.mysql_is_mariadb
+            and self.connection.mysql_version < (8,)
+        ):
+            skips.update(
+                {
+                    "Parenthesized combined queries are not supported on MySQL < 8 and "
+                    "MariaDB < 10.4": {
+                        "queries.test_qs_combinators.QuerySetSetOperationTests."
+                        "test_union_in_subquery",
+                        "queries.test_qs_combinators.QuerySetSetOperationTests."
+                        "test_union_in_subquery_related_outerref",
+                        "queries.test_qs_combinators.QuerySetSetOperationTests."
+                        "test_union_in_with_ordering",
+                    }
+                }
+            )
+        if not self.supports_explain_analyze:
+            skips.update(
+                {
+                    "MariaDB and MySQL >= 8.0.18 specific.": {
+                        "queries.test_explain.ExplainTests.test_mysql_analyze",
+                    },
+                }
+            )
+        return skips
+
+    @cached_property
+    def _mysql_storage_engine(self):
+        "Internal method used in Django tests. Don't rely on this from your code"
+        return self.connection.mysql_server_data["default_storage_engine"]
+
+    @cached_property
+    def allows_auto_pk_0(self):
+        """
+        Autoincrement primary key can be set to 0 if it doesn't generate new
+        autoincrement values.
+        """
+        return "NO_AUTO_VALUE_ON_ZERO" in self.connection.sql_mode
+
+    @cached_property
+    def update_can_self_select(self):
+        return self.connection.mysql_is_mariadb and self.connection.mysql_version >= (
+            10,
+            3,
+            2,
+        )
+
+    @cached_property
+    def can_introspect_foreign_keys(self):
+        "Confirm support for introspected foreign keys"
+        return self._mysql_storage_engine != "MyISAM"
+
+    @cached_property
+    def introspected_field_types(self):
+        return {
+            **super().introspected_field_types,
+            "BinaryField": "TextField",
+            "BooleanField": "IntegerField",
+            "DurationField": "BigIntegerField",
+            "GenericIPAddressField": "CharField",
+        }
+
+    @cached_property
+    def can_return_columns_from_insert(self):
+        return self.connection.mysql_is_mariadb and self.connection.mysql_version >= (
+            10,
+            5,
+            0,
+        )
+
+    can_return_rows_from_bulk_insert = property(
+        operator.attrgetter("can_return_columns_from_insert")
+    )
+
+    @cached_property
+    def has_zoneinfo_database(self):
+        return self.connection.mysql_server_data["has_zoneinfo_database"]
+
+    @cached_property
+    def is_sql_auto_is_null_enabled(self):
+        return self.connection.mysql_server_data["sql_auto_is_null"]
+
+    @cached_property
+    def supports_over_clause(self):
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (8, 0, 2)
+
+    supports_frame_range_fixed_distance = property(
+        operator.attrgetter("supports_over_clause")
+    )
+
+    @cached_property
+    def supports_column_check_constraints(self):
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (8, 0, 16)
+
+    supports_table_check_constraints = property(
+        operator.attrgetter("supports_column_check_constraints")
+    )
+
+    @cached_property
+    def can_introspect_check_constraints(self):
+        if self.connection.mysql_is_mariadb:
+            version = self.connection.mysql_version
+            return version >= (10, 3, 10)
+        return self.connection.mysql_version >= (8, 0, 16)
+
+    @cached_property
+    def has_select_for_update_skip_locked(self):
+        if self.connection.mysql_is_mariadb:
+            return self.connection.mysql_version >= (10, 6)
+        return self.connection.mysql_version >= (8, 0, 1)
+
+    @cached_property
+    def has_select_for_update_nowait(self):
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (8, 0, 1)
+
+    @cached_property
+    def has_select_for_update_of(self):
+        return (
+            not self.connection.mysql_is_mariadb
+            and self.connection.mysql_version >= (8, 0, 1)
+        )
+
+    @cached_property
+    def supports_explain_analyze(self):
+        return self.connection.mysql_is_mariadb or self.connection.mysql_version >= (
+            8,
+            0,
+            18,
+        )
+
+    @cached_property
+    def supported_explain_formats(self):
+        # Alias MySQL's TRADITIONAL to TEXT for consistency with other
+        # backends.
+        formats = {"JSON", "TEXT", "TRADITIONAL"}
+        if not self.connection.mysql_is_mariadb and self.connection.mysql_version >= (
+            8,
+            0,
+            16,
+        ):
+            formats.add("TREE")
+        return formats
+
+    @cached_property
+    def supports_transactions(self):
+        """
+        All storage engines except MyISAM support transactions.
+        """
+        return self._mysql_storage_engine != "MyISAM"
+
+    uses_savepoints = property(operator.attrgetter("supports_transactions"))
+    can_release_savepoints = property(operator.attrgetter("supports_transactions"))
+
+    @cached_property
+    def ignores_table_name_case(self):
+        return self.connection.mysql_server_data["lower_case_table_names"]
+
+    @cached_property
+    def supports_default_in_lead_lag(self):
+        # To be added in https://jira.mariadb.org/browse/MDEV-12981.
+        return not self.connection.mysql_is_mariadb
+
+    @cached_property
+    def supports_json_field(self):
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (5, 7, 8)
+
+    @cached_property
+    def can_introspect_json_field(self):
+        if self.connection.mysql_is_mariadb:
+            return self.supports_json_field and self.can_introspect_check_constraints
+        return self.supports_json_field
+
+    @cached_property
+    def supports_index_column_ordering(self):
+        if self._mysql_storage_engine != "InnoDB":
+            return False
+        if self.connection.mysql_is_mariadb:
+            return self.connection.mysql_version >= (10, 8)
+        return self.connection.mysql_version >= (8, 0, 1)
+
+    @cached_property
+    def supports_expression_indexes(self):
+        return (
+            not self.connection.mysql_is_mariadb
+            and self._mysql_storage_engine != "MyISAM"
+            and self.connection.mysql_version >= (8, 0, 13)
+        )
+
+    @cached_property
+    def can_rename_index(self):
+        if self.connection.mysql_is_mariadb:
+            return self.connection.mysql_version >= (10, 5, 2)
+        return True

env/lib/python3.8/site-packages/django/db/backends/mysql/introspection.py

@@ -0,0 +1,335 @@
+from collections import namedtuple
+
+import sqlparse
+from MySQLdb.constants import FIELD_TYPE
+
+from django.db.backends.base.introspection import BaseDatabaseIntrospection
+from django.db.backends.base.introspection import FieldInfo as BaseFieldInfo
+from django.db.backends.base.introspection import TableInfo
+from django.db.models import Index
+from django.utils.datastructures import OrderedSet
+
+FieldInfo = namedtuple(
+    "FieldInfo", BaseFieldInfo._fields + ("extra", "is_unsigned", "has_json_constraint")
+)
+InfoLine = namedtuple(
+    "InfoLine",
+    "col_name data_type max_len num_prec num_scale extra column_default "
+    "collation is_unsigned",
+)
+
+
+class DatabaseIntrospection(BaseDatabaseIntrospection):
+    data_types_reverse = {
+        FIELD_TYPE.BLOB: "TextField",
+        FIELD_TYPE.CHAR: "CharField",
+        FIELD_TYPE.DECIMAL: "DecimalField",
+        FIELD_TYPE.NEWDECIMAL: "DecimalField",
+        FIELD_TYPE.DATE: "DateField",
+        FIELD_TYPE.DATETIME: "DateTimeField",
+        FIELD_TYPE.DOUBLE: "FloatField",
+        FIELD_TYPE.FLOAT: "FloatField",
+        FIELD_TYPE.INT24: "IntegerField",
+        FIELD_TYPE.JSON: "JSONField",
+        FIELD_TYPE.LONG: "IntegerField",
+        FIELD_TYPE.LONGLONG: "BigIntegerField",
+        FIELD_TYPE.SHORT: "SmallIntegerField",
+        FIELD_TYPE.STRING: "CharField",
+        FIELD_TYPE.TIME: "TimeField",
+        FIELD_TYPE.TIMESTAMP: "DateTimeField",
+        FIELD_TYPE.TINY: "IntegerField",
+        FIELD_TYPE.TINY_BLOB: "TextField",
+        FIELD_TYPE.MEDIUM_BLOB: "TextField",
+        FIELD_TYPE.LONG_BLOB: "TextField",
+        FIELD_TYPE.VAR_STRING: "CharField",
+    }
+
+    def get_field_type(self, data_type, description):
+        field_type = super().get_field_type(data_type, description)
+        if "auto_increment" in description.extra:
+            if field_type == "IntegerField":
+                return "AutoField"
+            elif field_type == "BigIntegerField":
+                return "BigAutoField"
+            elif field_type == "SmallIntegerField":
+                return "SmallAutoField"
+        if description.is_unsigned:
+            if field_type == "BigIntegerField":
+                return "PositiveBigIntegerField"
+            elif field_type == "IntegerField":
+                return "PositiveIntegerField"
+            elif field_type == "SmallIntegerField":
+                return "PositiveSmallIntegerField"
+        # JSON data type is an alias for LONGTEXT in MariaDB, use check
+        # constraints clauses to introspect JSONField.
+        if description.has_json_constraint:
+            return "JSONField"
+        return field_type
+
+    def get_table_list(self, cursor):
+        """Return a list of table and view names in the current database."""
+        cursor.execute("SHOW FULL TABLES")
+        return [
+            TableInfo(row[0], {"BASE TABLE": "t", "VIEW": "v"}.get(row[1]))
+            for row in cursor.fetchall()
+        ]
+
+    def get_table_description(self, cursor, table_name):
+        """
+        Return a description of the table with the DB-API cursor.description
+        interface."
+        """
+        json_constraints = {}
+        if (
+            self.connection.mysql_is_mariadb
+            and self.connection.features.can_introspect_json_field
+        ):
+            # JSON data type is an alias for LONGTEXT in MariaDB, select
+            # JSON_VALID() constraints to introspect JSONField.
+            cursor.execute(
+                """
+                SELECT c.constraint_name AS column_name
+                FROM information_schema.check_constraints AS c
+                WHERE
+                    c.table_name = %s AND
+                    LOWER(c.check_clause) =
+                        'json_valid(`' + LOWER(c.constraint_name) + '`)' AND
+                    c.constraint_schema = DATABASE()
+                """,
+                [table_name],
+            )
+            json_constraints = {row[0] for row in cursor.fetchall()}
+        # A default collation for the given table.
+        cursor.execute(
+            """
+            SELECT  table_collation
+            FROM    information_schema.tables
+            WHERE   table_schema = DATABASE()
+            AND     table_name = %s
+            """,
+            [table_name],
+        )
+        row = cursor.fetchone()
+        default_column_collation = row[0] if row else ""
+        # information_schema database gives more accurate results for some figures:
+        # - varchar length returned by cursor.description is an internal length,
+        #   not visible length (#5725)
+        # - precision and scale (for decimal fields) (#5014)
+        # - auto_increment is not available in cursor.description
+        cursor.execute(
+            """
+            SELECT
+                column_name, data_type, character_maximum_length,
+                numeric_precision, numeric_scale, extra, column_default,
+                CASE
+                    WHEN collation_name = %s THEN NULL
+                    ELSE collation_name
+                END AS collation_name,
+                CASE
+                    WHEN column_type LIKE '%% unsigned' THEN 1
+                    ELSE 0
+                END AS is_unsigned
+            FROM information_schema.columns
+            WHERE table_name = %s AND table_schema = DATABASE()
+            """,
+            [default_column_collation, table_name],
+        )
+        field_info = {line[0]: InfoLine(*line) for line in cursor.fetchall()}
+
+        cursor.execute(
+            "SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name)
+        )
+
+        def to_int(i):
+            return int(i) if i is not None else i
+
+        fields = []
+        for line in cursor.description:
+            info = field_info[line[0]]
+            fields.append(
+                FieldInfo(
+                    *line[:3],
+                    to_int(info.max_len) or line[3],
+                    to_int(info.num_prec) or line[4],
+                    to_int(info.num_scale) or line[5],
+                    line[6],
+                    info.column_default,
+                    info.collation,
+                    info.extra,
+                    info.is_unsigned,
+                    line[0] in json_constraints,
+                )
+            )
+        return fields
+
+    def get_sequences(self, cursor, table_name, table_fields=()):
+        for field_info in self.get_table_description(cursor, table_name):
+            if "auto_increment" in field_info.extra:
+                # MySQL allows only one auto-increment column per table.
+                return [{"table": table_name, "column": field_info.name}]
+        return []
+
+    def get_relations(self, cursor, table_name):
+        """
+        Return a dictionary of {field_name: (field_name_other_table, other_table)}
+        representing all foreign keys in the given table.
+        """
+        cursor.execute(
+            """
+            SELECT column_name, referenced_column_name, referenced_table_name
+            FROM information_schema.key_column_usage
+            WHERE table_name = %s
+                AND table_schema = DATABASE()
+                AND referenced_table_name IS NOT NULL
+                AND referenced_column_name IS NOT NULL
+            """,
+            [table_name],
+        )
+        return {
+            field_name: (other_field, other_table)
+            for field_name, other_field, other_table in cursor.fetchall()
+        }
+
+    def get_storage_engine(self, cursor, table_name):
+        """
+        Retrieve the storage engine for a given table. Return the default
+        storage engine if the table doesn't exist.
+        """
+        cursor.execute(
+            """
+            SELECT engine
+            FROM information_schema.tables
+            WHERE
+                table_name = %s AND
+                table_schema = DATABASE()
+            """,
+            [table_name],
+        )
+        result = cursor.fetchone()
+        if not result:
+            return self.connection.features._mysql_storage_engine
+        return result[0]
+
+    def _parse_constraint_columns(self, check_clause, columns):
+        check_columns = OrderedSet()
+        statement = sqlparse.parse(check_clause)[0]
+        tokens = (token for token in statement.flatten() if not token.is_whitespace)
+        for token in tokens:
+            if (
+                token.ttype == sqlparse.tokens.Name
+                and self.connection.ops.quote_name(token.value) == token.value
+                and token.value[1:-1] in columns
+            ):
+                check_columns.add(token.value[1:-1])
+        return check_columns
+
+    def get_constraints(self, cursor, table_name):
+        """
+        Retrieve any constraints or keys (unique, pk, fk, check, index) across
+        one or more columns.
+        """
+        constraints = {}
+        # Get the actual constraint names and columns
+        name_query = """
+            SELECT kc.`constraint_name`, kc.`column_name`,
+                kc.`referenced_table_name`, kc.`referenced_column_name`,
+                c.`constraint_type`
+            FROM
+                information_schema.key_column_usage AS kc,
+                information_schema.table_constraints AS c
+            WHERE
+                kc.table_schema = DATABASE() AND
+                c.table_schema = kc.table_schema AND
+                c.constraint_name = kc.constraint_name AND
+                c.constraint_type != 'CHECK' AND
+                kc.table_name = %s
+            ORDER BY kc.`ordinal_position`
+        """
+        cursor.execute(name_query, [table_name])
+        for constraint, column, ref_table, ref_column, kind in cursor.fetchall():
+            if constraint not in constraints:
+                constraints[constraint] = {
+                    "columns": OrderedSet(),
+                    "primary_key": kind == "PRIMARY KEY",
+                    "unique": kind in {"PRIMARY KEY", "UNIQUE"},
+                    "index": False,
+                    "check": False,
+                    "foreign_key": (ref_table, ref_column) if ref_column else None,
+                }
+                if self.connection.features.supports_index_column_ordering:
+                    constraints[constraint]["orders"] = []
+            constraints[constraint]["columns"].add(column)
+        # Add check constraints.
+        if self.connection.features.can_introspect_check_constraints:
+            unnamed_constraints_index = 0
+            columns = {
+                info.name for info in self.get_table_description(cursor, table_name)
+            }
+            if self.connection.mysql_is_mariadb:
+                type_query = """
+                    SELECT c.constraint_name, c.check_clause
+                    FROM information_schema.check_constraints AS c
+                    WHERE
+                        c.constraint_schema = DATABASE() AND
+                        c.table_name = %s
+                """
+            else:
+                type_query = """
+                    SELECT cc.constraint_name, cc.check_clause
+                    FROM
+                        information_schema.check_constraints AS cc,
+                        information_schema.table_constraints AS tc
+                    WHERE
+                        cc.constraint_schema = DATABASE() AND
+                        tc.table_schema = cc.constraint_schema AND
+                        cc.constraint_name = tc.constraint_name AND
+                        tc.constraint_type = 'CHECK' AND
+                        tc.table_name = %s
+                """
+            cursor.execute(type_query, [table_name])
+            for constraint, check_clause in cursor.fetchall():
+                constraint_columns = self._parse_constraint_columns(
+                    check_clause, columns
+                )
+                # Ensure uniqueness of unnamed constraints. Unnamed unique
+                # and check columns constraints have the same name as
+                # a column.
+                if set(constraint_columns) == {constraint}:
+                    unnamed_constraints_index += 1
+                    constraint = "__unnamed_constraint_%s__" % unnamed_constraints_index
+                constraints[constraint] = {
+                    "columns": constraint_columns,
+                    "primary_key": False,
+                    "unique": False,
+                    "index": False,
+                    "check": True,
+                    "foreign_key": None,
+                }
+        # Now add in the indexes
+        cursor.execute(
+            "SHOW INDEX FROM %s" % self.connection.ops.quote_name(table_name)
+        )
+        for table, non_unique, index, colseq, column, order, type_ in [
+            x[:6] + (x[10],) for x in cursor.fetchall()
+        ]:
+            if index not in constraints:
+                constraints[index] = {
+                    "columns": OrderedSet(),
+                    "primary_key": False,
+                    "unique": not non_unique,
+                    "check": False,
+                    "foreign_key": None,
+                }
+                if self.connection.features.supports_index_column_ordering:
+                    constraints[index]["orders"] = []
+            constraints[index]["index"] = True
+            constraints[index]["type"] = (
+                Index.suffix if type_ == "BTREE" else type_.lower()
+            )
+            constraints[index]["columns"].add(column)
+            if self.connection.features.supports_index_column_ordering:
+                constraints[index]["orders"].append("DESC" if order == "D" else "ASC")
+        # Convert the sorted sets to lists
+        for constraint in constraints.values():
+            constraint["columns"] = list(constraint["columns"])
+        return constraints

env/lib/python3.8/site-packages/django/db/backends/mysql/operations.py

@@ -0,0 +1,467 @@
+import uuid
+
+from django.conf import settings
+from django.db.backends.base.operations import BaseDatabaseOperations
+from django.db.backends.utils import split_tzname_delta
+from django.db.models import Exists, ExpressionWrapper, Lookup
+from django.db.models.constants import OnConflict
+from django.utils import timezone
+from django.utils.encoding import force_str
+from django.utils.regex_helper import _lazy_re_compile
+
+
+class DatabaseOperations(BaseDatabaseOperations):
+    compiler_module = "django.db.backends.mysql.compiler"
+
+    # MySQL stores positive fields as UNSIGNED ints.
+    integer_field_ranges = {
+        **BaseDatabaseOperations.integer_field_ranges,
+        "PositiveSmallIntegerField": (0, 65535),
+        "PositiveIntegerField": (0, 4294967295),
+        "PositiveBigIntegerField": (0, 18446744073709551615),
+    }
+    cast_data_types = {
+        "AutoField": "signed integer",
+        "BigAutoField": "signed integer",
+        "SmallAutoField": "signed integer",
+        "CharField": "char(%(max_length)s)",
+        "DecimalField": "decimal(%(max_digits)s, %(decimal_places)s)",
+        "TextField": "char",
+        "IntegerField": "signed integer",
+        "BigIntegerField": "signed integer",
+        "SmallIntegerField": "signed integer",
+        "PositiveBigIntegerField": "unsigned integer",
+        "PositiveIntegerField": "unsigned integer",
+        "PositiveSmallIntegerField": "unsigned integer",
+        "DurationField": "signed integer",
+    }
+    cast_char_field_without_max_length = "char"
+    explain_prefix = "EXPLAIN"
+
+    # EXTRACT format cannot be passed in parameters.
+    _extract_format_re = _lazy_re_compile(r"[A-Z_]+")
+
+    def date_extract_sql(self, lookup_type, sql, params):
+        # https://dev.mysql.com/doc/mysql/en/date-and-time-functions.html
+        if lookup_type == "week_day":
+            # DAYOFWEEK() returns an integer, 1-7, Sunday=1.
+            return f"DAYOFWEEK({sql})", params
+        elif lookup_type == "iso_week_day":
+            # WEEKDAY() returns an integer, 0-6, Monday=0.
+            return f"WEEKDAY({sql}) + 1", params
+        elif lookup_type == "week":
+            # Override the value of default_week_format for consistency with
+            # other database backends.
+            # Mode 3: Monday, 1-53, with 4 or more days this year.
+            return f"WEEK({sql}, 3)", params
+        elif lookup_type == "iso_year":
+            # Get the year part from the YEARWEEK function, which returns a
+            # number as year * 100 + week.
+            return f"TRUNCATE(YEARWEEK({sql}, 3), -2) / 100", params
+        else:
+            # EXTRACT returns 1-53 based on ISO-8601 for the week number.
+            lookup_type = lookup_type.upper()
+            if not self._extract_format_re.fullmatch(lookup_type):
+                raise ValueError(f"Invalid loookup type: {lookup_type!r}")
+            return f"EXTRACT({lookup_type} FROM {sql})", params
+
+    def date_trunc_sql(self, lookup_type, sql, params, tzname=None):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        fields = {
+            "year": "%Y-01-01",
+            "month": "%Y-%m-01",
+        }
+        if lookup_type in fields:
+            format_str = fields[lookup_type]
+            return f"CAST(DATE_FORMAT({sql}, %s) AS DATE)", (*params, format_str)
+        elif lookup_type == "quarter":
+            return (
+                f"MAKEDATE(YEAR({sql}), 1) + "
+                f"INTERVAL QUARTER({sql}) QUARTER - INTERVAL 1 QUARTER",
+                (*params, *params),
+            )
+        elif lookup_type == "week":
+            return f"DATE_SUB({sql}, INTERVAL WEEKDAY({sql}) DAY)", (*params, *params)
+        else:
+            return f"DATE({sql})", params
+
+    def _prepare_tzname_delta(self, tzname):
+        tzname, sign, offset = split_tzname_delta(tzname)
+        return f"{sign}{offset}" if offset else tzname
+
+    def _convert_sql_to_tz(self, sql, params, tzname):
+        if tzname and settings.USE_TZ and self.connection.timezone_name != tzname:
+            return f"CONVERT_TZ({sql}, %s, %s)", (
+                *params,
+                self.connection.timezone_name,
+                self._prepare_tzname_delta(tzname),
+            )
+        return sql, params
+
+    def datetime_cast_date_sql(self, sql, params, tzname):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        return f"DATE({sql})", params
+
+    def datetime_cast_time_sql(self, sql, params, tzname):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        return f"TIME({sql})", params
+
+    def datetime_extract_sql(self, lookup_type, sql, params, tzname):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        return self.date_extract_sql(lookup_type, sql, params)
+
+    def datetime_trunc_sql(self, lookup_type, sql, params, tzname):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        fields = ["year", "month", "day", "hour", "minute", "second"]
+        format = ("%Y-", "%m", "-%d", " %H:", "%i", ":%s")
+        format_def = ("0000-", "01", "-01", " 00:", "00", ":00")
+        if lookup_type == "quarter":
+            return (
+                f"CAST(DATE_FORMAT(MAKEDATE(YEAR({sql}), 1) + "
+                f"INTERVAL QUARTER({sql}) QUARTER - "
+                f"INTERVAL 1 QUARTER, %s) AS DATETIME)"
+            ), (*params, *params, "%Y-%m-01 00:00:00")
+        if lookup_type == "week":
+            return (
+                f"CAST(DATE_FORMAT("
+                f"DATE_SUB({sql}, INTERVAL WEEKDAY({sql}) DAY), %s) AS DATETIME)"
+            ), (*params, *params, "%Y-%m-%d 00:00:00")
+        try:
+            i = fields.index(lookup_type) + 1
+        except ValueError:
+            pass
+        else:
+            format_str = "".join(format[:i] + format_def[i:])
+            return f"CAST(DATE_FORMAT({sql}, %s) AS DATETIME)", (*params, format_str)
+        return sql, params
+
+    def time_trunc_sql(self, lookup_type, sql, params, tzname=None):
+        sql, params = self._convert_sql_to_tz(sql, params, tzname)
+        fields = {
+            "hour": "%H:00:00",
+            "minute": "%H:%i:00",
+            "second": "%H:%i:%s",
+        }
+        if lookup_type in fields:
+            format_str = fields[lookup_type]
+            return f"CAST(DATE_FORMAT({sql}, %s) AS TIME)", (*params, format_str)
+        else:
+            return f"TIME({sql})", params
+
+    def fetch_returned_insert_rows(self, cursor):
+        """
+        Given a cursor object that has just performed an INSERT...RETURNING
+        statement into a table, return the tuple of returned data.
+        """
+        return cursor.fetchall()
+
+    def format_for_duration_arithmetic(self, sql):
+        return "INTERVAL %s MICROSECOND" % sql
+
+    def force_no_ordering(self):
+        """
+        "ORDER BY NULL" prevents MySQL from implicitly ordering by grouped
+        columns. If no ordering would otherwise be applied, we don't want any
+        implicit sorting going on.
+        """
+        return [(None, ("NULL", [], False))]
+
+    def adapt_decimalfield_value(self, value, max_digits=None, decimal_places=None):
+        return value
+
+    def last_executed_query(self, cursor, sql, params):
+        # With MySQLdb, cursor objects have an (undocumented) "_executed"
+        # attribute where the exact query sent to the database is saved.
+        # See MySQLdb/cursors.py in the source distribution.
+        # MySQLdb returns string, PyMySQL bytes.
+        return force_str(getattr(cursor, "_executed", None), errors="replace")
+
+    def no_limit_value(self):
+        # 2**64 - 1, as recommended by the MySQL documentation
+        return 18446744073709551615
+
+    def quote_name(self, name):
+        if name.startswith("`") and name.endswith("`"):
+            return name  # Quoting once is enough.
+        return "`%s`" % name
+
+    def return_insert_columns(self, fields):
+        # MySQL and MariaDB < 10.5.0 don't support an INSERT...RETURNING
+        # statement.
+        if not fields:
+            return "", ()
+        columns = [
+            "%s.%s"
+            % (
+                self.quote_name(field.model._meta.db_table),
+                self.quote_name(field.column),
+            )
+            for field in fields
+        ]
+        return "RETURNING %s" % ", ".join(columns), ()
+
+    def sql_flush(self, style, tables, *, reset_sequences=False, allow_cascade=False):
+        if not tables:
+            return []
+
+        sql = ["SET FOREIGN_KEY_CHECKS = 0;"]
+        if reset_sequences:
+            # It's faster to TRUNCATE tables that require a sequence reset
+            # since ALTER TABLE AUTO_INCREMENT is slower than TRUNCATE.
+            sql.extend(
+                "%s %s;"
+                % (
+                    style.SQL_KEYWORD("TRUNCATE"),
+                    style.SQL_FIELD(self.quote_name(table_name)),
+                )
+                for table_name in tables
+            )
+        else:
+            # Otherwise issue a simple DELETE since it's faster than TRUNCATE
+            # and preserves sequences.
+            sql.extend(
+                "%s %s %s;"
+                % (
+                    style.SQL_KEYWORD("DELETE"),
+                    style.SQL_KEYWORD("FROM"),
+                    style.SQL_FIELD(self.quote_name(table_name)),
+                )
+                for table_name in tables
+            )
+        sql.append("SET FOREIGN_KEY_CHECKS = 1;")
+        return sql
+
+    def sequence_reset_by_name_sql(self, style, sequences):
+        return [
+            "%s %s %s %s = 1;"
+            % (
+                style.SQL_KEYWORD("ALTER"),
+                style.SQL_KEYWORD("TABLE"),
+                style.SQL_FIELD(self.quote_name(sequence_info["table"])),
+                style.SQL_FIELD("AUTO_INCREMENT"),
+            )
+            for sequence_info in sequences
+        ]
+
+    def validate_autopk_value(self, value):
+        # Zero in AUTO_INCREMENT field does not work without the
+        # NO_AUTO_VALUE_ON_ZERO SQL mode.
+        if value == 0 and not self.connection.features.allows_auto_pk_0:
+            raise ValueError(
+                "The database backend does not accept 0 as a value for AutoField."
+            )
+        return value
+
+    def adapt_datetimefield_value(self, value):
+        if value is None:
+            return None
+
+        # Expression values are adapted by the database.
+        if hasattr(value, "resolve_expression"):
+            return value
+
+        # MySQL doesn't support tz-aware datetimes
+        if timezone.is_aware(value):
+            if settings.USE_TZ:
+                value = timezone.make_naive(value, self.connection.timezone)
+            else:
+                raise ValueError(
+                    "MySQL backend does not support timezone-aware datetimes when "
+                    "USE_TZ is False."
+                )
+        return str(value)
+
+    def adapt_timefield_value(self, value):
+        if value is None:
+            return None
+
+        # Expression values are adapted by the database.
+        if hasattr(value, "resolve_expression"):
+            return value
+
+        # MySQL doesn't support tz-aware times
+        if timezone.is_aware(value):
+            raise ValueError("MySQL backend does not support timezone-aware times.")
+
+        return value.isoformat(timespec="microseconds")
+
+    def max_name_length(self):
+        return 64
+
+    def pk_default_value(self):
+        return "NULL"
+
+    def bulk_insert_sql(self, fields, placeholder_rows):
+        placeholder_rows_sql = (", ".join(row) for row in placeholder_rows)
+        values_sql = ", ".join("(%s)" % sql for sql in placeholder_rows_sql)
+        return "VALUES " + values_sql
+
+    def combine_expression(self, connector, sub_expressions):
+        if connector == "^":
+            return "POW(%s)" % ",".join(sub_expressions)
+        # Convert the result to a signed integer since MySQL's binary operators
+        # return an unsigned integer.
+        elif connector in ("&", "|", "<<", "#"):
+            connector = "^" if connector == "#" else connector
+            return "CONVERT(%s, SIGNED)" % connector.join(sub_expressions)
+        elif connector == ">>":
+            lhs, rhs = sub_expressions
+            return "FLOOR(%(lhs)s / POW(2, %(rhs)s))" % {"lhs": lhs, "rhs": rhs}
+        return super().combine_expression(connector, sub_expressions)
+
+    def get_db_converters(self, expression):
+        converters = super().get_db_converters(expression)
+        internal_type = expression.output_field.get_internal_type()
+        if internal_type == "BooleanField":
+            converters.append(self.convert_booleanfield_value)
+        elif internal_type == "DateTimeField":
+            if settings.USE_TZ:
+                converters.append(self.convert_datetimefield_value)
+        elif internal_type == "UUIDField":
+            converters.append(self.convert_uuidfield_value)
+        return converters
+
+    def convert_booleanfield_value(self, value, expression, connection):
+        if value in (0, 1):
+            value = bool(value)
+        return value
+
+    def convert_datetimefield_value(self, value, expression, connection):
+        if value is not None:
+            value = timezone.make_aware(value, self.connection.timezone)
+        return value
+
+    def convert_uuidfield_value(self, value, expression, connection):
+        if value is not None:
+            value = uuid.UUID(value)
+        return value
+
+    def binary_placeholder_sql(self, value):
+        return (
+            "_binary %s" if value is not None and not hasattr(value, "as_sql") else "%s"
+        )
+
+    def subtract_temporals(self, internal_type, lhs, rhs):
+        lhs_sql, lhs_params = lhs
+        rhs_sql, rhs_params = rhs
+        if internal_type == "TimeField":
+            if self.connection.mysql_is_mariadb:
+                # MariaDB includes the microsecond component in TIME_TO_SEC as
+                # a decimal. MySQL returns an integer without microseconds.
+                return (
+                    "CAST((TIME_TO_SEC(%(lhs)s) - TIME_TO_SEC(%(rhs)s)) "
+                    "* 1000000 AS SIGNED)"
+                ) % {
+                    "lhs": lhs_sql,
+                    "rhs": rhs_sql,
+                }, (
+                    *lhs_params,
+                    *rhs_params,
+                )
+            return (
+                "((TIME_TO_SEC(%(lhs)s) * 1000000 + MICROSECOND(%(lhs)s)) -"
+                " (TIME_TO_SEC(%(rhs)s) * 1000000 + MICROSECOND(%(rhs)s)))"
+            ) % {"lhs": lhs_sql, "rhs": rhs_sql}, tuple(lhs_params) * 2 + tuple(
+                rhs_params
+            ) * 2
+        params = (*rhs_params, *lhs_params)
+        return "TIMESTAMPDIFF(MICROSECOND, %s, %s)" % (rhs_sql, lhs_sql), params
+
+    def explain_query_prefix(self, format=None, **options):
+        # Alias MySQL's TRADITIONAL to TEXT for consistency with other backends.
+        if format and format.upper() == "TEXT":
+            format = "TRADITIONAL"
+        elif (
+            not format and "TREE" in self.connection.features.supported_explain_formats
+        ):
+            # Use TREE by default (if supported) as it's more informative.
+            format = "TREE"
+        analyze = options.pop("analyze", False)
+        prefix = super().explain_query_prefix(format, **options)
+        if analyze and self.connection.features.supports_explain_analyze:
+            # MariaDB uses ANALYZE instead of EXPLAIN ANALYZE.
+            prefix = (
+                "ANALYZE" if self.connection.mysql_is_mariadb else prefix + " ANALYZE"
+            )
+        if format and not (analyze and not self.connection.mysql_is_mariadb):
+            # Only MariaDB supports the analyze option with formats.
+            prefix += " FORMAT=%s" % format
+        return prefix
+
+    def regex_lookup(self, lookup_type):
+        # REGEXP BINARY doesn't work correctly in MySQL 8+ and REGEXP_LIKE
+        # doesn't exist in MySQL 5.x or in MariaDB.
+        if (
+            self.connection.mysql_version < (8, 0, 0)
+            or self.connection.mysql_is_mariadb
+        ):
+            if lookup_type == "regex":
+                return "%s REGEXP BINARY %s"
+            return "%s REGEXP %s"
+
+        match_option = "c" if lookup_type == "regex" else "i"
+        return "REGEXP_LIKE(%%s, %%s, '%s')" % match_option
+
+    def insert_statement(self, on_conflict=None):
+        if on_conflict == OnConflict.IGNORE:
+            return "INSERT IGNORE INTO"
+        return super().insert_statement(on_conflict=on_conflict)
+
+    def lookup_cast(self, lookup_type, internal_type=None):
+        lookup = "%s"
+        if internal_type == "JSONField":
+            if self.connection.mysql_is_mariadb or lookup_type in (
+                "iexact",
+                "contains",
+                "icontains",
+                "startswith",
+                "istartswith",
+                "endswith",
+                "iendswith",
+                "regex",
+                "iregex",
+            ):
+                lookup = "JSON_UNQUOTE(%s)"
+        return lookup
+
+    def conditional_expression_supported_in_where_clause(self, expression):
+        # MySQL ignores indexes with boolean fields unless they're compared
+        # directly to a boolean value.
+        if isinstance(expression, (Exists, Lookup)):
+            return True
+        if isinstance(expression, ExpressionWrapper) and expression.conditional:
+            return self.conditional_expression_supported_in_where_clause(
+                expression.expression
+            )
+        if getattr(expression, "conditional", False):
+            return False
+        return super().conditional_expression_supported_in_where_clause(expression)
+
+    def on_conflict_suffix_sql(self, fields, on_conflict, update_fields, unique_fields):
+        if on_conflict == OnConflict.UPDATE:
+            conflict_suffix_sql = "ON DUPLICATE KEY UPDATE %(fields)s"
+            field_sql = "%(field)s = VALUES(%(field)s)"
+            # The use of VALUES() is deprecated in MySQL 8.0.20+. Instead, use
+            # aliases for the new row and its columns available in MySQL
+            # 8.0.19+.
+            if not self.connection.mysql_is_mariadb:
+                if self.connection.mysql_version >= (8, 0, 19):
+                    conflict_suffix_sql = f"AS new {conflict_suffix_sql}"
+                    field_sql = "%(field)s = new.%(field)s"
+            # VALUES() was renamed to VALUE() in MariaDB 10.3.3+.
+            elif self.connection.mysql_version >= (10, 3, 3):
+                field_sql = "%(field)s = VALUE(%(field)s)"
+
+            fields = ", ".join(
+                [
+                    field_sql % {"field": field}
+                    for field in map(self.quote_name, update_fields)
+                ]
+            )
+            return conflict_suffix_sql % {"fields": fields}
+        return super().on_conflict_suffix_sql(
+            fields,
+            on_conflict,
+            update_fields,
+            unique_fields,
+        )

env/lib/python3.8/site-packages/django/db/backends/mysql/schema.py

@@ -0,0 +1,175 @@
+from django.db.backends.base.schema import BaseDatabaseSchemaEditor
+from django.db.models import NOT_PROVIDED
+
+
+class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
+
+    sql_rename_table = "RENAME TABLE %(old_table)s TO %(new_table)s"
+
+    sql_alter_column_null = "MODIFY %(column)s %(type)s NULL"
+    sql_alter_column_not_null = "MODIFY %(column)s %(type)s NOT NULL"
+    sql_alter_column_type = "MODIFY %(column)s %(type)s"
+    sql_alter_column_collate = "MODIFY %(column)s %(type)s%(collation)s"
+    sql_alter_column_no_default_null = "ALTER COLUMN %(column)s SET DEFAULT NULL"
+
+    # No 'CASCADE' which works as a no-op in MySQL but is undocumented
+    sql_delete_column = "ALTER TABLE %(table)s DROP COLUMN %(column)s"
+
+    sql_delete_unique = "ALTER TABLE %(table)s DROP INDEX %(name)s"
+    sql_create_column_inline_fk = (
+        ", ADD CONSTRAINT %(name)s FOREIGN KEY (%(column)s) "
+        "REFERENCES %(to_table)s(%(to_column)s)"
+    )
+    sql_delete_fk = "ALTER TABLE %(table)s DROP FOREIGN KEY %(name)s"
+
+    sql_delete_index = "DROP INDEX %(name)s ON %(table)s"
+    sql_rename_index = "ALTER TABLE %(table)s RENAME INDEX %(old_name)s TO %(new_name)s"
+
+    sql_create_pk = (
+        "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s PRIMARY KEY (%(columns)s)"
+    )
+    sql_delete_pk = "ALTER TABLE %(table)s DROP PRIMARY KEY"
+
+    sql_create_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s)%(extra)s"
+
+    @property
+    def sql_delete_check(self):
+        if self.connection.mysql_is_mariadb:
+            # The name of the column check constraint is the same as the field
+            # name on MariaDB. Adding IF EXISTS clause prevents migrations
+            # crash. Constraint is removed during a "MODIFY" column statement.
+            return "ALTER TABLE %(table)s DROP CONSTRAINT IF EXISTS %(name)s"
+        return "ALTER TABLE %(table)s DROP CHECK %(name)s"
+
+    @property
+    def sql_rename_column(self):
+        # MariaDB >= 10.5.2 and MySQL >= 8.0.4 support an
+        # "ALTER TABLE ... RENAME COLUMN" statement.
+        if self.connection.mysql_is_mariadb:
+            if self.connection.mysql_version >= (10, 5, 2):
+                return super().sql_rename_column
+        elif self.connection.mysql_version >= (8, 0, 4):
+            return super().sql_rename_column
+        return "ALTER TABLE %(table)s CHANGE %(old_column)s %(new_column)s %(type)s"
+
+    def quote_value(self, value):
+        self.connection.ensure_connection()
+        if isinstance(value, str):
+            value = value.replace("%", "%%")
+        # MySQLdb escapes to string, PyMySQL to bytes.
+        quoted = self.connection.connection.escape(
+            value, self.connection.connection.encoders
+        )
+        if isinstance(value, str) and isinstance(quoted, bytes):
+            quoted = quoted.decode()
+        return quoted
+
+    def _is_limited_data_type(self, field):
+        db_type = field.db_type(self.connection)
+        return (
+            db_type is not None
+            and db_type.lower() in self.connection._limited_data_types
+        )
+
+    def skip_default(self, field):
+        if not self._supports_limited_data_type_defaults:
+            return self._is_limited_data_type(field)
+        return False
+
+    def skip_default_on_alter(self, field):
+        if self._is_limited_data_type(field) and not self.connection.mysql_is_mariadb:
+            # MySQL doesn't support defaults for BLOB and TEXT in the
+            # ALTER COLUMN statement.
+            return True
+        return False
+
+    @property
+    def _supports_limited_data_type_defaults(self):
+        # MariaDB and MySQL >= 8.0.13 support defaults for BLOB and TEXT.
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (8, 0, 13)
+
+    def _column_default_sql(self, field):
+        if (
+            not self.connection.mysql_is_mariadb
+            and self._supports_limited_data_type_defaults
+            and self._is_limited_data_type(field)
+        ):
+            # MySQL supports defaults for BLOB and TEXT columns only if the
+            # default value is written as an expression i.e. in parentheses.
+            return "(%s)"
+        return super()._column_default_sql(field)
+
+    def add_field(self, model, field):
+        super().add_field(model, field)
+
+        # Simulate the effect of a one-off default.
+        # field.default may be unhashable, so a set isn't used for "in" check.
+        if self.skip_default(field) and field.default not in (None, NOT_PROVIDED):
+            effective_default = self.effective_default(field)
+            self.execute(
+                "UPDATE %(table)s SET %(column)s = %%s"
+                % {
+                    "table": self.quote_name(model._meta.db_table),
+                    "column": self.quote_name(field.column),
+                },
+                [effective_default],
+            )
+
+    def _field_should_be_indexed(self, model, field):
+        if not super()._field_should_be_indexed(model, field):
+            return False
+
+        storage = self.connection.introspection.get_storage_engine(
+            self.connection.cursor(), model._meta.db_table
+        )
+        # No need to create an index for ForeignKey fields except if
+        # db_constraint=False because the index from that constraint won't be
+        # created.
+        if (
+            storage == "InnoDB"
+            and field.get_internal_type() == "ForeignKey"
+            and field.db_constraint
+        ):
+            return False
+        return not self._is_limited_data_type(field)
+
+    def _delete_composed_index(self, model, fields, *args):
+        """
+        MySQL can remove an implicit FK index on a field when that field is
+        covered by another index like a unique_together. "covered" here means
+        that the more complex index starts like the simpler one.
+        https://bugs.mysql.com/bug.php?id=37910 / Django ticket #24757
+        We check here before removing the [unique|index]_together if we have to
+        recreate a FK index.
+        """
+        first_field = model._meta.get_field(fields[0])
+        if first_field.get_internal_type() == "ForeignKey":
+            constraint_names = self._constraint_names(
+                model, [first_field.column], index=True
+            )
+            if not constraint_names:
+                self.execute(
+                    self._create_index_sql(model, fields=[first_field], suffix="")
+                )
+        return super()._delete_composed_index(model, fields, *args)
+
+    def _set_field_new_type_null_status(self, field, new_type):
+        """
+        Keep the null property of the old field. If it has changed, it will be
+        handled separately.
+        """
+        if field.null:
+            new_type += " NULL"
+        else:
+            new_type += " NOT NULL"
+        return new_type
+
+    def _alter_column_type_sql(self, model, old_field, new_field, new_type):
+        new_type = self._set_field_new_type_null_status(old_field, new_type)
+        return super()._alter_column_type_sql(model, old_field, new_field, new_type)
+
+    def _rename_field_sql(self, table, old_field, new_field, new_type):
+        new_type = self._set_field_new_type_null_status(old_field, new_type)
+        return super()._rename_field_sql(table, old_field, new_field, new_type)

env/lib/python3.8/site-packages/django/db/backends/mysql/validation.py

@@ -0,0 +1,77 @@
+from django.core import checks
+from django.db.backends.base.validation import BaseDatabaseValidation
+from django.utils.version import get_docs_version
+
+
+class DatabaseValidation(BaseDatabaseValidation):
+    def check(self, **kwargs):
+        issues = super().check(**kwargs)
+        issues.extend(self._check_sql_mode(**kwargs))
+        return issues
+
+    def _check_sql_mode(self, **kwargs):
+        if not (
+            self.connection.sql_mode & {"STRICT_TRANS_TABLES", "STRICT_ALL_TABLES"}
+        ):
+            return [
+                checks.Warning(
+                    "%s Strict Mode is not set for database connection '%s'"
+                    % (self.connection.display_name, self.connection.alias),
+                    hint=(
+                        "%s's Strict Mode fixes many data integrity problems in "
+                        "%s, such as data truncation upon insertion, by "
+                        "escalating warnings into errors. It is strongly "
+                        "recommended you activate it. See: "
+                        "https://docs.djangoproject.com/en/%s/ref/databases/"
+                        "#mysql-sql-mode"
+                        % (
+                            self.connection.display_name,
+                            self.connection.display_name,
+                            get_docs_version(),
+                        ),
+                    ),
+                    id="mysql.W002",
+                )
+            ]
+        return []
+
+    def check_field_type(self, field, field_type):
+        """
+        MySQL has the following field length restriction:
+        No character (varchar) fields can have a length exceeding 255
+        characters if they have a unique index on them.
+        MySQL doesn't support a database index on some data types.
+        """
+        errors = []
+        if (
+            field_type.startswith("varchar")
+            and field.unique
+            and (field.max_length is None or int(field.max_length) > 255)
+        ):
+            errors.append(
+                checks.Warning(
+                    "%s may not allow unique CharFields to have a max_length "
+                    "> 255." % self.connection.display_name,
+                    obj=field,
+                    hint=(
+                        "See: https://docs.djangoproject.com/en/%s/ref/"
+                        "databases/#mysql-character-fields" % get_docs_version()
+                    ),
+                    id="mysql.W003",
+                )
+            )
+
+        if field.db_index and field_type.lower() in self.connection._limited_data_types:
+            errors.append(
+                checks.Warning(
+                    "%s does not support a database index on %s columns."
+                    % (self.connection.display_name, field_type),
+                    hint=(
+                        "An index won't be created. Silence this warning if "
+                        "you don't care about it."
+                    ),
+                    obj=field,
+                    id="fields.W162",
+                )
+            )
+        return errors