# Copyright (c) Microsoft Corporation.
# Licensed under the BSD license.

"""
MS SQL Server database backend for Django.
"""
import os
import re
import time
import struct
import datetime
from decimal import Decimal
from uuid import UUID

from django.core.exceptions import ImproperlyConfigured
from django.utils.functional import cached_property

try:
    import pyodbc as Database
except ImportError as e:
    raise ImproperlyConfigured("Error loading pyodbc module: %s" % e)

from django.utils.version import get_version_tuple  # noqa

pyodbc_ver = get_version_tuple(Database.version)
if pyodbc_ver < (3, 0):
    raise ImproperlyConfigured("pyodbc 3.0 or newer is required; you have %s" % Database.version)

from django.conf import settings  # noqa
from django.db import NotSupportedError  # noqa
from django.db.backends.base.base import BaseDatabaseWrapper  # noqa
from django.utils.encoding import smart_str  # noqa
from django.utils.functional import cached_property  # noqa

if hasattr(settings, 'DATABASE_CONNECTION_POOLING'):
    if not settings.DATABASE_CONNECTION_POOLING:
        Database.pooling = False

from .client import DatabaseClient  # noqa
from .creation import DatabaseCreation  # noqa
from .features import DatabaseFeatures  # noqa
from .introspection import DatabaseIntrospection, SQL_TIMESTAMP_WITH_TIMEZONE  # noqa
from .operations import DatabaseOperations  # noqa
from .schema import DatabaseSchemaEditor  # noqa

EDITION_AZURE_SQL_DB = 5
EDITION_AZURE_SQL_MANAGED_INSTANCE = 8

def encode_connection_string(fields):
    """Encode dictionary of keys and values as an ODBC connection String.

    See [MS-ODBCSTR] document:
    https://msdn.microsoft.com/en-us/library/ee208909%28v=sql.105%29.aspx
    """
    # As the keys are all provided by us, don't need to encode them as we know
    # they are ok.
    return ';'.join(
        '%s=%s' % (k, encode_value(v))
        for k, v in fields.items()
    )
def prepare_token_for_odbc(token):
    """
    Will prepare token for passing it to the odbc driver, as it expects
    bytes and not a string
    :param token:
    :return: packed binary byte representation of token string
    """
    if not isinstance(token, str):
        raise TypeError("Invalid token format provided.")

    tokenstr = token.encode()
    exptoken = b""
    for i in tokenstr:
        exptoken += bytes({i})
        exptoken += bytes(1)
    return struct.pack("=i", len(exptoken)) + exptoken

def encode_value(v):
    """If the value contains a semicolon, or starts with a left curly brace,
    then enclose it in curly braces and escape all right curly braces.
    """
    if ';' in v or v.strip(' ').startswith('{'):
        return '{%s}' % (v.replace('}', '}}'),)
    return v


def handle_datetimeoffset(dto_value):
    # Decode bytes returned from SQL Server
    # source: https://github.com/mkleehammer/pyodbc/wiki/Using-an-Output-Converter-function
    tup = struct.unpack("<6hI2h", dto_value)  # e.g., (2017, 3, 16, 10, 35, 18, 500000000)
    return datetime.datetime(tup[0], tup[1], tup[2], tup[3], tup[4], tup[5], tup[6] // 1000)


class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'microsoft'
    display_name = 'SQL Server'
    # This dictionary maps Field objects to their associated MS SQL 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': 'int',
        'BigAutoField': 'bigint',
        'BigIntegerField': 'bigint',
        'BinaryField': 'varbinary(%(max_length)s)',
        'BooleanField': 'bit',
        'CharField': 'nvarchar(%(max_length)s)',
        'DateField': 'date',
        'DateTimeField': 'datetime2',
        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
        'DurationField': 'bigint',
        'FileField': 'nvarchar(%(max_length)s)',
        'FilePathField': 'nvarchar(%(max_length)s)',
        'FloatField': 'double precision',
        'IntegerField': 'int',
        'IPAddressField': 'nvarchar(15)',
        'GenericIPAddressField': 'nvarchar(39)',
        'JSONField': 'nvarchar(max)',
        'NullBooleanField': 'bit',
        'OneToOneField': 'int',
        'PositiveIntegerField': 'int',
        'PositiveSmallIntegerField': 'smallint',
        'PositiveBigIntegerField' : 'bigint',
        'SlugField': 'nvarchar(%(max_length)s)',
        'SmallAutoField': 'smallint',
        'SmallIntegerField': 'smallint',
        'TextField': 'nvarchar(max)',
        'TimeField': 'time',
        'UUIDField': 'char(32)',
    }
    data_types_suffix = {
        'AutoField': 'IDENTITY (1, 1)',
        'BigAutoField': 'IDENTITY (1, 1)',
        'SmallAutoField': 'IDENTITY (1, 1)',
    }
    data_type_check_constraints = {
        'JSONField': '(ISJSON ("%(column)s") = 1)',
        'PositiveIntegerField': '[%(column)s] >= 0',
        'PositiveSmallIntegerField': '[%(column)s] >= 0',
        'PositiveBigIntegerField': '[%(column)s] >= 0',
    }
    operators = {
        # Since '=' is used not only for string comparision there is no way
        # to make it case (in)sensitive.
        'exact': '= %s',
        'iexact': "= UPPER(%s)",
        'contains': "LIKE %s ESCAPE '\\'",
        'icontains': "LIKE UPPER(%s) ESCAPE '\\'",
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': "LIKE %s ESCAPE '\\'",
        'endswith': "LIKE %s ESCAPE '\\'",
        'istartswith': "LIKE UPPER(%s) ESCAPE '\\'",
        'iendswith': "LIKE UPPER(%s) ESCAPE '\\'",
    }

    # 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 '%%' + {} + '%%'",
        'icontains': "LIKE '%%' + UPPER({}) + '%%'",
        'startswith': "LIKE {} + '%%'",
        'istartswith': "LIKE UPPER({}) + '%%'",
        'endswith': "LIKE '%%' + {}",
        'iendswith': "LIKE '%%' + UPPER({})",
    }

    Database = Database
    SchemaEditorClass = DatabaseSchemaEditor
    # Classes instantiated in __init__().
    client_class = DatabaseClient
    creation_class = DatabaseCreation
    features_class = DatabaseFeatures
    introspection_class = DatabaseIntrospection
    ops_class = DatabaseOperations

    _codes_for_networkerror = (
        '08S01',
        '08S02',
    )
    _sql_server_versions = {
        9: 2005,
        10: 2008,
        11: 2012,
        12: 2014,
        13: 2016,
        14: 2017,
        15: 2019,
        16: 2022,
    }

    # https://azure.microsoft.com/en-us/documentation/articles/sql-database-develop-csharp-retry-windows/
    _transient_error_numbers = (
        '4060',
        '10928',
        '10929',
        '40197',
        '40501',
        '40613',
        '49918',
        '49919',
        '49920',
    )

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        opts = self.settings_dict["OPTIONS"]

        # capability for multiple result sets or cursors
        self.supports_mars = False

        # Some drivers need unicode encoded as UTF8. If this is left as
        # None, it will be determined based on the driver, namely it'll be
        # False if the driver is a windows driver and True otherwise.
        #
        # However, recent versions of FreeTDS and pyodbc (0.91 and 3.0.6 as
        # of writing) are perfectly okay being fed unicode, which is why
        # this option is configurable.
        if 'driver_needs_utf8' in opts:
            self.driver_charset = 'utf-8'
        else:
            self.driver_charset = opts.get('driver_charset', None)

        # interval to wait for recovery from network error
        interval = opts.get('connection_recovery_interval_msec', 0.0)
        self.connection_recovery_interval_msec = float(interval) / 1000

        # make lookup operators to be collation-sensitive if needed
        collation = opts.get('collation', None)
        if collation:
            self.operators = dict(self.__class__.operators)
            ops = {}
            for op in self.operators:
                sql = self.operators[op]
                if sql.startswith('LIKE '):
                    ops[op] = '%s COLLATE %s' % (sql, collation)
            self.operators.update(ops)

        if (settings.USE_TZ):
            self.data_types['DateTimeField'] ='datetimeoffset'

    def create_cursor(self, name=None):
        return CursorWrapper(self.connection.cursor(), self)

    def _cursor(self):
        new_conn = False

        if self.connection is None:
            new_conn = True

        conn = super()._cursor()
        if new_conn:
            if self.sql_server_version <= 2005:
                self.data_types['DateField'] = 'datetime'
                self.data_types['DateTimeField'] = 'datetime'
                self.data_types['TimeField'] = 'datetime'

        return conn

    def get_connection_params(self):
        settings_dict = self.settings_dict
        if settings_dict['NAME'] == '':
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        conn_params = settings_dict.copy()
        if conn_params['NAME'] is None:
            conn_params['NAME'] = 'master'
        return conn_params

    def get_new_connection(self, conn_params):
        database = conn_params['NAME']
        host = conn_params.get('HOST', 'localhost')
        user = conn_params.get('USER', None)
        password = conn_params.get('PASSWORD', None)
        port = conn_params.get('PORT', None)
        trusted_connection = conn_params.get('Trusted_Connection', 'yes')

        options = conn_params.get('OPTIONS', {})
        driver = options.get('driver', 'ODBC Driver 17 for SQL Server')
        dsn = options.get('dsn', None)
        options_extra_params = options.get('extra_params', '')

        # Microsoft driver names assumed here are:
        # * SQL Server Native Client 10.0/11.0
        # * ODBC Driver 11/13 for SQL Server
        ms_drivers = re.compile('^ODBC Driver .* for SQL Server$|^SQL Server Native Client')

        # available ODBC connection string keywords:
        # (Microsoft drivers for Windows)
        # https://docs.microsoft.com/en-us/sql/relational-databases/native-client/applications/using-connection-string-keywords-with-sql-server-native-client
        # (Microsoft drivers for Linux/Mac)
        # https://docs.microsoft.com/en-us/sql/connect/odbc/linux-mac/connection-string-keywords-and-data-source-names-dsns
        # (FreeTDS)
        # http://www.freetds.org/userguide/odbcconnattr.htm
        cstr_parts = {}
        if dsn:
            cstr_parts['DSN'] = dsn
        else:
            # Only append DRIVER if DATABASE_ODBC_DSN hasn't been set
            cstr_parts['DRIVER'] = driver

            if ms_drivers.match(driver):
                if port:
                    host = ','.join((host, str(port)))
                cstr_parts['SERVER'] = host
            elif options.get('host_is_server', False):
                if port:
                    cstr_parts['PORT'] = str(port)
                cstr_parts['SERVER'] = host
            else:
                cstr_parts['SERVERNAME'] = host

        if user:
            cstr_parts['UID'] = user
            if 'Authentication=ActiveDirectoryInteractive' not in options_extra_params:
                cstr_parts['PWD'] = password
        elif 'TOKEN' not in conn_params:
            if ms_drivers.match(driver) and 'Authentication=ActiveDirectoryMsi' not in options_extra_params:
                cstr_parts['Trusted_Connection'] = trusted_connection
            else:
                cstr_parts['Integrated Security'] = 'SSPI'

        cstr_parts['DATABASE'] = database

        if ms_drivers.match(driver) and os.name == 'nt':
            cstr_parts['MARS_Connection'] = 'yes'

        connstr = encode_connection_string(cstr_parts)

        # extra_params are glued on the end of the string without encoding,
        # so it's up to the settings writer to make sure they're appropriate -
        # use encode_connection_string if constructing from external input.
        if options.get('extra_params', None):
            connstr += ';' + options['extra_params']

        unicode_results = options.get('unicode_results', False)
        timeout = options.get('connection_timeout', 0)
        retries = options.get('connection_retries', 5)
        backoff_time = options.get('connection_retry_backoff_time', 5)
        query_timeout = options.get('query_timeout', 0)
        setencoding = options.get('setencoding', None)
        setdecoding = options.get('setdecoding', None)

        conn = None
        retry_count = 0
        need_to_retry = False
        args = {
            'unicode_results': unicode_results,
            'timeout': timeout,
        }
        if 'TOKEN' in conn_params:
            args['attrs_before'] = {
                1256: prepare_token_for_odbc(conn_params['TOKEN'])
            }
        while conn is None:
            try:
                conn = Database.connect(connstr, **args)
            except Exception as e:
                for error_number in self._transient_error_numbers:
                    if error_number in e.args[1]:
                        if error_number in e.args[1] and retry_count < retries:
                            time.sleep(backoff_time)
                            need_to_retry = True
                            retry_count = retry_count + 1
                        else:
                            need_to_retry = False
                        break
                if not need_to_retry:
                    raise
        # Handling values from DATETIMEOFFSET columns
        # source: https://github.com/mkleehammer/pyodbc/wiki/Using-an-Output-Converter-function
        conn.add_output_converter(SQL_TIMESTAMP_WITH_TIMEZONE, handle_datetimeoffset)
        conn.timeout = query_timeout
        if setencoding:
            for entry in setencoding:
                conn.setencoding(**entry)
        if setdecoding:
            for entry in setdecoding:
                conn.setdecoding(**entry)
        return conn

    def init_connection_state(self):
        drv_name = self.connection.getinfo(Database.SQL_DRIVER_NAME).upper()

        if drv_name.startswith('LIBTDSODBC'):
            try:
                drv_ver = self.connection.getinfo(Database.SQL_DRIVER_VER)
                ver = get_version_tuple(drv_ver)[:2]
                if ver < (0, 95):
                    raise ImproperlyConfigured(
                        "FreeTDS 0.95 or newer is required.")
            except Exception:
                # unknown driver version
                pass

        ms_drv_names = re.compile('^(LIB)?(SQLNCLI|MSODBCSQL)')

        if ms_drv_names.match(drv_name):
            self.driver_charset = None
            # http://msdn.microsoft.com/en-us/library/ms131686.aspx
            self.supports_mars = True
            self.features.can_use_chunked_reads = True

        settings_dict = self.settings_dict
        cursor = self.create_cursor()

        options = settings_dict.get('OPTIONS', {})
        isolation_level = options.get('isolation_level', None)
        if isolation_level:
            cursor.execute('SET TRANSACTION ISOLATION LEVEL %s' % isolation_level)

        # Set date format for the connection. Also, make sure Sunday is
        # considered the first day of the week (to be consistent with the
        # Django convention for the 'week_day' Django lookup) if the user
        # hasn't told us otherwise
        datefirst = options.get('datefirst', 7)
        cursor.execute('SET DATEFORMAT ymd; SET DATEFIRST %s' % datefirst)

        # Let user choose if driver can return rows from bulk insert since
        # inserting into tables with triggers causes errors. See issue #130
        if (options.get('return_rows_bulk_insert', False)):
            self.features_class.can_return_rows_from_bulk_insert = True

        val = self.get_system_datetime
        if isinstance(val, str):
            raise ImproperlyConfigured(
                "The database driver doesn't support modern datatime types.")

    def is_usable(self):
        try:
            self.create_cursor().execute("SELECT 1")
        except Database.Error:
            return False
        else:
            return True

    @cached_property
    def get_system_datetime(self):
        # http://blogs.msdn.com/b/sqlnativeclient/archive/2008/02/27/microsoft-sql-server-native-client-and-microsoft-sql-server-2008-native-client.aspx
        with self.temporary_connection() as cursor:
            if self.sql_server_version <= 2005:
                return cursor.execute('SELECT GETDATE()').fetchone()[0]
            else:
                return cursor.execute('SELECT SYSDATETIME()').fetchone()[0]

    @cached_property
    def sql_server_version(self, _known_versions={}):
        """
        Get the SQL server version

        The _known_versions default dictionary is created on the class. This is
        intentional - it allows us to cache this property's value across instances.
        Therefore, when Django creates a new database connection using the same
        alias, we won't need query the server again.
        """
        if self.alias not in _known_versions:
            with self.temporary_connection() as cursor:
                cursor.execute("SELECT CAST(SERVERPROPERTY('ProductVersion') AS varchar)")
                ver = cursor.fetchone()[0]
                ver = int(ver.split('.')[0])
                if ver not in self._sql_server_versions:
                    raise NotSupportedError('SQL Server v%d is not supported.' % ver)
                _known_versions[self.alias] = self._sql_server_versions[ver]
        return _known_versions[self.alias]

    @cached_property
    def to_azure_sql_db(self, _known_azures={}):
        """
        Whether this connection is to a Microsoft Azure database server

        The _known_azures default dictionary is created on the class. This is
        intentional - it allows us to cache this property's value across instances.
        Therefore, when Django creates a new database connection using the same
        alias, we won't need query the server again.
        """
        if self.alias not in _known_azures:
            with self.temporary_connection() as cursor:
                cursor.execute("SELECT CAST(SERVERPROPERTY('EngineEdition') AS integer)")
                edition = cursor.fetchone()[0]
                _known_azures[self.alias] = edition == EDITION_AZURE_SQL_DB or edition == EDITION_AZURE_SQL_MANAGED_INSTANCE
        return _known_azures[self.alias]

    def _execute_foreach(self, sql, table_names=None):
        cursor = self.cursor()
        if table_names is None:
            table_names = self.introspection.table_names(cursor)
        for table_name in table_names:
            cursor.execute(sql % self.ops.quote_name(table_name))

    def _get_trancount(self):
        with self.connection.cursor() as cursor:
            return cursor.execute('SELECT @@TRANCOUNT').fetchone()[0]

    def _on_error(self, e):
        if e.args[0] in self._codes_for_networkerror:
            try:
                # close the stale connection
                self.close()
                # wait a moment for recovery from network error
                time.sleep(self.connection_recovery_interval_msec)
            except Exception:
                pass
            self.connection = None

    def _savepoint(self, sid):
        with self.cursor() as cursor:
            cursor.execute('SELECT @@TRANCOUNT')
            trancount = cursor.fetchone()[0]
            if trancount == 0:
                cursor.execute(self.ops.start_transaction_sql())
            cursor.execute(self.ops.savepoint_create_sql(sid))

    def _savepoint_commit(self, sid):
        # SQL Server has no support for partial commit in a transaction
        pass

    def _savepoint_rollback(self, sid):
        with self.cursor() as cursor:
            # FreeTDS requires TRANCOUNT that is greater than 0
            cursor.execute('SELECT @@TRANCOUNT')
            trancount = cursor.fetchone()[0]
            if trancount > 0:
                cursor.execute(self.ops.savepoint_rollback_sql(sid))

    def _set_autocommit(self, autocommit):
        with self.wrap_database_errors:
            allowed = not autocommit
            if not allowed:
                # FreeTDS requires TRANCOUNT that is greater than 0
                allowed = self._get_trancount() > 0
            if allowed:
                self.connection.autocommit = autocommit

    def check_constraints(self, table_names=None):
        self._execute_foreach('ALTER TABLE %s WITH CHECK CHECK CONSTRAINT ALL',
                              table_names)

    def disable_constraint_checking(self):
        if not self.needs_rollback:
            self._execute_foreach('ALTER TABLE %s NOCHECK CONSTRAINT ALL')
        return not self.needs_rollback

    def enable_constraint_checking(self):
        if not self.needs_rollback:
            self._execute_foreach('ALTER TABLE %s WITH NOCHECK CHECK CONSTRAINT ALL')


class CursorWrapper(object):
    """
    A wrapper around the pyodbc's cursor that takes in account a) some pyodbc
    DB-API 2.0 implementation and b) some common ODBC driver particularities.
    """

    def __init__(self, cursor, connection):
        self.active = True
        self.cursor = cursor
        self.connection = connection
        self.driver_charset = connection.driver_charset
        self.last_sql = ''
        self.last_params = ()

    def _as_sql_type(self, typ, value):
        if isinstance(value, str):
            length = len(value)
            if length == 0:
                return 'NVARCHAR'
            elif length > 4000:
                return 'NVARCHAR(max)'
            return 'NVARCHAR(%s)' % len(value)
        elif typ == int:
            if value < 0x7FFFFFFF and value > -0x7FFFFFFF:
                return 'INT'
            else:
                return 'BIGINT'
        elif typ == float:
            return 'DOUBLE PRECISION'
        elif typ == bool:
            return 'BIT'
        elif isinstance(value, Decimal):
            return 'NUMERIC'
        elif isinstance(value, datetime.datetime):
            return 'DATETIME2'
        elif isinstance(value, datetime.date):
            return 'DATE'
        elif isinstance(value, datetime.time):
            return 'TIME'
        elif isinstance(value, UUID):
            return 'uniqueidentifier'
        elif isinstance(value, bytes):
            return 'VARBINARY'
        else:
            raise NotImplementedError('Not supported type %s (%s)' % (type(value), repr(value)))

    def close(self):
        if self.active:
            self.active = False
            self.cursor.close()

    def format_sql(self, sql, params):
        if self.driver_charset and isinstance(sql, str):
            # FreeTDS (and other ODBC drivers?) doesn't support Unicode
            # yet, so we need to encode the SQL clause itself in utf-8
            sql = smart_str(sql, self.driver_charset)

        # pyodbc uses '?' instead of '%s' as parameter placeholder.
        if params is not None and params != []:
            sql = sql % tuple('?' * len(params))

        return sql

    def format_group_by_params(self, query, params):
        # Prepare query for string formatting
        query = re.sub(r'%\w+', '{}', query)

        if params:
            # Insert None params directly into the query
            if None in params:
                null_params = ['NULL' if param is None else '{}' for param in params]
                query = query.format(*null_params)
                params = tuple(p for p in params if p is not None)
            params = [(param, type(param)) for param in params]
            params_dict = {param: '@var%d' % i for i, param in enumerate(set(params))}
            args = [params_dict[param] for param in params]

            variables = []
            params = []
            for key, value in params_dict.items():
                datatype = self._as_sql_type(key[1], key[0])
                variables.append("%s %s = %%s " % (value, datatype))
                params.append(key[0])
            query = ('DECLARE %s \n' % ','.join(variables)) + (query.format(*args))
        return query, params

    def format_params(self, params):
        fp = []
        if params is not None:
            for p in params:
                if isinstance(p, str):
                    if self.driver_charset:
                        # FreeTDS (and other ODBC drivers?) doesn't support Unicode
                        # yet, so we need to encode parameters in utf-8
                        fp.append(smart_str(p, self.driver_charset))
                    else:
                        fp.append(p)

                elif isinstance(p, bytes):
                    fp.append(p)

                elif isinstance(p, type(True)):
                    if p:
                        fp.append(1)
                    else:
                        fp.append(0)

                else:
                    fp.append(p)

        return tuple(fp)

    def execute(self, sql, params=None):
        self.last_sql = sql
        if 'GROUP BY' in sql:
            sql, params = self.format_group_by_params(sql, params)
        sql = self.format_sql(sql, params)
        params = self.format_params(params)
        self.last_params = params
        try:
            return self.cursor.execute(sql, params)
        except Database.Error as e:
            self.connection._on_error(e)
            raise

    def executemany(self, sql, params_list=()):
        if not params_list:
            return None
        raw_pll = [p for p in params_list]
        sql = self.format_sql(sql, raw_pll[0])
        params_list = [self.format_params(p) for p in raw_pll]
        try:
            return self.cursor.executemany(sql, params_list)
        except Database.Error as e:
            self.connection._on_error(e)
            raise

    def format_rows(self, rows):
        return list(map(self.format_row, rows))

    def format_row(self, row):
        """
        Decode data coming from the database if needed and convert rows to tuples
        (pyodbc Rows are not hashable).
        """
        if self.driver_charset:
            for i in range(len(row)):
                f = row[i]
                # FreeTDS (and other ODBC drivers?) doesn't support Unicode
                # yet, so we need to decode utf-8 data coming from the DB
                if isinstance(f, bytes):
                    row[i] = f.decode(self.driver_charset)
        return tuple(row)

    def fetchone(self):
        row = self.cursor.fetchone()
        if row is not None:
            row = self.format_row(row)
        # Any remaining rows in the current set must be discarded
        # before changing autocommit mode when you use FreeTDS
        if not self.connection.supports_mars:
            self.cursor.nextset()
        return row

    def fetchmany(self, chunk):
        return self.format_rows(self.cursor.fetchmany(chunk))

    def fetchall(self):
        return self.format_rows(self.cursor.fetchall())

    def __getattr__(self, attr):
        if attr in self.__dict__:
            return self.__dict__[attr]
        return getattr(self.cursor, attr)

    def __iter__(self):
        return iter(self.cursor)