Python operations.DatabaseOperations类代码示例

    def test_lookup_cast(self):
        from django.db.backends.postgresql_psycopg2.operations import DatabaseOperations

        do = DatabaseOperations(connection=None)
        for lookup in ('iexact', 'contains', 'icontains', 'startswith',
                       'istartswith', 'endswith', 'iendswith', 'regex', 'iregex'):
            self.assertIn('::text', do.lookup_cast(lookup))

    def test_lookup_cast(self):
        from django.db.backends.postgresql_psycopg2.operations import DatabaseOperations

        do = DatabaseOperations(connection=None)
        for lookup in (
            "iexact",
            "contains",
            "icontains",
            "startswith",
            "istartswith",
            "endswith",
            "iendswith",
            "regex",
            "iregex",
        ):
            self.assertIn("::text", do.lookup_cast(lookup))

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

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

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

        opts = self.settings_dict["OPTIONS"]
        RC = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self.isolation_level = opts.get('isolation_level', RC)

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

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

        self.features = DatabaseFeatures(self)
        autocommit = self.settings_dict["OPTIONS"].get('autocommit', False)
        self.features.uses_autocommit = autocommit
        if autocommit:
            level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
        else:
            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self._set_isolation_level(level)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

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

        settings_dict = self.settings_dict

        self.features = DatabaseFeatures(self)
        autocommit = settings_dict["OPTIONS"].get('autocommit', False)
        self.features.uses_autocommit = autocommit
        if autocommit:
            level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
        else:
            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self._set_isolation_level(level)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)
        self._pg_version = None

        if not settings_dict['NAME']:
            from django.core.exceptions import ImproperlyConfigured
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")

        try:
            self.pool = _pools[self.alias]
        except KeyError:
            conn_params = {
                'database': settings_dict['NAME'],
            }
            conn_params.update(settings_dict['OPTIONS'])
            if 'autocommit' in conn_params:
                del conn_params['autocommit']
            if settings_dict['USER']:
                conn_params['user'] = settings_dict['USER']
            if settings_dict['PASSWORD']:
                conn_params['password'] = force_str(settings_dict['PASSWORD'])
            if settings_dict['HOST']:
                conn_params['host'] = settings_dict['HOST']
            if settings_dict['PORT']:
                conn_params['port'] = settings_dict['PORT']

            self.pool = GeventConnectionPool(1, DB_POOL_MAX_CONN, **conn_params)
            _pools[self.alias] = self.pool

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

        self.features = DatabaseFeatures(self)
        autocommit = self.settings_dict["OPTIONS"].get('autocommit', False)
        self.features.uses_autocommit = autocommit
        if autocommit:
            level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
        else:
            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self._set_isolation_level(level)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)
        self._pg_version = None
        self.conn_params = self._conn_params()
        if self.alias not in POOLS:
            self.pool = POOLS[self.alias] = PostgresConnectionPool(maxsize=1000, **self.conn_params)
        else:
            self.pool = POOLS[self.alias]

class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'postgresql'
    operators = {
        'exact': '= %s',
        'iexact': '= UPPER(%s)',
        'contains': 'LIKE %s',
        'icontains': 'LIKE UPPER(%s)',
        'regex': '~ %s',
        'iregex': '~* %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE %s',
        'endswith': 'LIKE %s',
        'istartswith': 'LIKE UPPER(%s)',
        'iendswith': 'LIKE UPPER(%s)',
    }

    pattern_ops = {
        'startswith': "LIKE %s || '%%%%'",
        'istartswith': "LIKE UPPER(%s) || '%%%%'",
    }

    Database = Database

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

        opts = self.settings_dict["OPTIONS"]
        RC = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self.isolation_level = opts.get('isolation_level', RC)

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

    def get_connection_params(self):
        settings_dict = self.settings_dict
        # None may be used to connect to the default 'postgres' db
        if settings_dict['NAME'] == '':
            from django.core.exceptions import ImproperlyConfigured
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        conn_params = {
            'database': settings_dict['NAME'] or 'postgres',
        }
        conn_params.update(settings_dict['OPTIONS'])
        if 'autocommit' in conn_params:
            del conn_params['autocommit']
        if 'isolation_level' in conn_params:
            del conn_params['isolation_level']
        if settings_dict['USER']:
            conn_params['user'] = settings_dict['USER']
        if settings_dict['PASSWORD']:
            conn_params['password'] = force_str(settings_dict['PASSWORD'])
        if settings_dict['HOST']:
            conn_params['host'] = settings_dict['HOST']
        if settings_dict['PORT']:
            conn_params['port'] = settings_dict['PORT']
        return conn_params

    def get_new_connection(self, conn_params):
        return Database.connect(**conn_params)

    def init_connection_state(self):
        settings_dict = self.settings_dict
        self.connection.set_client_encoding('UTF8')
        tz = 'UTC' if settings.USE_TZ else settings_dict.get('TIME_ZONE')
        if tz:
            try:
                get_parameter_status = self.connection.get_parameter_status
            except AttributeError:
                # psycopg2 < 2.0.12 doesn't have get_parameter_status
                conn_tz = None
            else:
                conn_tz = get_parameter_status('TimeZone')

            if conn_tz != tz:
                cursor = self.connection.cursor()
                try:
                    cursor.execute(self.ops.set_time_zone_sql(), [tz])
                finally:
                    cursor.close()
                # Commit after setting the time zone (see #17062)
                if not self.get_autocommit():
                    self.connection.commit()

    def create_cursor(self):
        cursor = self.connection.cursor()
        cursor.tzinfo_factory = utc_tzinfo_factory if settings.USE_TZ else None
        return cursor

    def _set_isolation_level(self, isolation_level):
        assert isolation_level in range(1, 5)     # Use set_autocommit for level = 0
        if self.psycopg2_version >= (2, 4, 2):
#.........这里部分代码省略.........

class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'postgresql'
    operators = {
        'exact': '= %s',
        'iexact': '= UPPER(%s)',
        'contains': 'LIKE %s',
        'icontains': 'LIKE UPPER(%s)',
        'regex': '~ %s',
        'iregex': '~* %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE %s',
        'endswith': 'LIKE %s',
        'istartswith': 'LIKE UPPER(%s)',
        'iendswith': 'LIKE UPPER(%s)',
    }

    Database = Database

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

        self.features = DatabaseFeatures(self)
        autocommit = self.settings_dict["OPTIONS"].get('autocommit', False)
        self.features.uses_autocommit = autocommit
        if autocommit:
            level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
        else:
            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self._set_isolation_level(level)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

    def check_constraints(self, table_names=None):
        """
        To check constraints, we set constraints to immediate. Then, when, we're done we must ensure they
        are returned to deferred.
        """
        self.cursor().execute('SET CONSTRAINTS ALL IMMEDIATE')
        self.cursor().execute('SET CONSTRAINTS ALL DEFERRED')

    def close(self):
        self.validate_thread_sharing()
        if self.connection is None:
            return

        try:
            self.connection.close()
            self.connection = None
        except Database.Error:
            # In some cases (database restart, network connection lost etc...)
            # the connection to the database is lost without giving Django a
            # notification. If we don't set self.connection to None, the error
            # will occur a every request.
            self.connection = None
            logger.warning('psycopg2 error while closing the connection.',
                exc_info=sys.exc_info()
            )
            raise
        finally:
            self.set_clean()

    @cached_property
    def pg_version(self):
        with self.temporary_connection():
            return get_version(self.connection)

    def get_connection_params(self):
        settings_dict = self.settings_dict
        if not settings_dict['NAME']:
            from django.core.exceptions import ImproperlyConfigured
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        conn_params = {
            'database': settings_dict['NAME'],
        }
        conn_params.update(settings_dict['OPTIONS'])
        if 'autocommit' in conn_params:
            del conn_params['autocommit']
        if settings_dict['USER']:
            conn_params['user'] = settings_dict['USER']
        if settings_dict['PASSWORD']:
            conn_params['password'] = force_str(settings_dict['PASSWORD'])
        if settings_dict['HOST']:
            conn_params['host'] = settings_dict['HOST']
        if settings_dict['PORT']:
            conn_params['port'] = settings_dict['PORT']
        return conn_params

    def get_new_connection(self, conn_params):
        return Database.connect(**conn_params)

    def init_connection_state(self):
        settings_dict = self.settings_dict
#.........这里部分代码省略.........

class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'postgresql'
    operators = {
        'exact': '= %s',
        'iexact': '= UPPER(%s)',
        'contains': 'LIKE %s',
        'icontains': 'LIKE UPPER(%s)',
        'regex': '~ %s',
        'iregex': '~* %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE %s',
        'endswith': 'LIKE %s',
        'istartswith': 'LIKE UPPER(%s)',
        'iendswith': 'LIKE UPPER(%s)',
    }

    Database = Database

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

        opts = self.settings_dict["OPTIONS"]
        RC = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self.isolation_level = opts.get('isolation_level', RC)

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

    def get_connection_params(self):
        settings_dict = self.settings_dict
        if not settings_dict['NAME']:
            from django.core.exceptions import ImproperlyConfigured
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        conn_params = {
            'database': settings_dict['NAME'],
        }
        conn_params.update(settings_dict['OPTIONS'])
        if 'autocommit' in conn_params:
            del conn_params['autocommit']
        if 'isolation_level' in conn_params:
            del conn_params['isolation_level']
        if settings_dict['USER']:
            conn_params['user'] = settings_dict['USER']
        if settings_dict['PASSWORD']:
            conn_params['password'] = force_str(settings_dict['PASSWORD'])
        if settings_dict['HOST']:
            conn_params['host'] = settings_dict['HOST']
        if settings_dict['PORT']:
            conn_params['port'] = settings_dict['PORT']
        return conn_params

    def get_new_connection(self, conn_params):
        return Database.connect(**conn_params)

    def init_connection_state(self):
        settings_dict = self.settings_dict
        self.connection.set_client_encoding('UTF8')
        tz = 'UTC' if settings.USE_TZ else settings_dict.get('TIME_ZONE')
        if tz:
            try:
                get_parameter_status = self.connection.get_parameter_status
            except AttributeError:
                # psycopg2 < 2.0.12 doesn't have get_parameter_status
                conn_tz = None
            else:
                conn_tz = get_parameter_status('TimeZone')

            if conn_tz != tz:
                # Set the time zone in autocommit mode (see #17062)
                self.set_autocommit(True)
                self.connection.cursor().execute(
                    self.ops.set_time_zone_sql(), [tz]
                )
        self.connection.set_isolation_level(self.isolation_level)

    def create_cursor(self):
        cursor = self.connection.cursor()
        cursor.tzinfo_factory = utc_tzinfo_factory if settings.USE_TZ else None
        return cursor

    def close(self):
        self.validate_thread_sharing()
        if self.connection is None:
            return

        try:
            self.connection.close()
            self.connection = None
        except Database.Error:
            # In some cases (database restart, network connection lost etc...)
            # the connection to the database is lost without giving Django a
#.........这里部分代码省略.........

class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = 'postgresql'
    # This dictionary maps Field objects to their associated PostgreSQL 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': 'serial',
        'BinaryField': 'bytea',
        'BooleanField': 'boolean',
        'CharField': 'varchar(%(max_length)s)',
        'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
        'DateField': 'date',
        'DateTimeField': 'timestamp with time zone',
        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
        'DurationField': 'interval',
        'FileField': 'varchar(%(max_length)s)',
        'FilePathField': 'varchar(%(max_length)s)',
        'FloatField': 'double precision',
        'IntegerField': 'integer',
        'BigIntegerField': 'bigint',
        'IPAddressField': 'inet',
        'GenericIPAddressField': 'inet',
        'NullBooleanField': 'boolean',
        'OneToOneField': 'integer',
        'PositiveIntegerField': 'integer',
        'PositiveSmallIntegerField': 'smallint',
        'SlugField': 'varchar(%(max_length)s)',
        'SmallIntegerField': 'smallint',
        'TextField': 'text',
        'TimeField': 'time',
        'UUIDField': 'uuid',
    }
    data_type_check_constraints = {
        'PositiveIntegerField': '"%(column)s" >= 0',
        'PositiveSmallIntegerField': '"%(column)s" >= 0',
    }
    operators = {
        'exact': '= %s',
        'iexact': '= UPPER(%s)',
        'contains': 'LIKE %s',
        'icontains': 'LIKE UPPER(%s)',
        'regex': '~ %s',
        'iregex': '~* %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE %s',
        'endswith': 'LIKE %s',
        'istartswith': 'LIKE UPPER(%s)',
        'iendswith': 'LIKE UPPER(%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 '%%' || {} || '%%'",
        'icontains': "LIKE '%%' || UPPER({}) || '%%'",
        'startswith': "LIKE {} || '%%'",
        'istartswith': "LIKE UPPER({}) || '%%'",
        'endswith': "LIKE '%%' || {}",
        'iendswith': "LIKE '%%' || UPPER({})",
    }

    Database = Database
    SchemaEditorClass = DatabaseSchemaEditor

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

        opts = self.settings_dict["OPTIONS"]
        RC = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self.isolation_level = opts.get('isolation_level', RC)

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

    def get_connection_params(self):
        settings_dict = self.settings_dict
        # None may be used to connect to the default 'postgres' db
        if settings_dict['NAME'] == '':
            from django.core.exceptions import ImproperlyConfigured
            raise ImproperlyConfigured(
                "settings.DATABASES is improperly configured. "
                "Please supply the NAME value.")
        conn_params = {
            'database': settings_dict['NAME'] or 'postgres',
        }
#.........这里部分代码省略.........

class DatabaseWrapper(BaseDatabaseWrapper):
    vendor = "postgresql"
    operators = {
        "exact": "= %s",
        "iexact": "= UPPER(%s)",
        "contains": "LIKE %s",
        "icontains": "LIKE UPPER(%s)",
        "regex": "~ %s",
        "iregex": "~* %s",
        "gt": "> %s",
        "gte": ">= %s",
        "lt": "< %s",
        "lte": "<= %s",
        "startswith": "LIKE %s",
        "endswith": "LIKE %s",
        "istartswith": "LIKE UPPER(%s)",
        "iendswith": "LIKE UPPER(%s)",
    }

    pattern_ops = {"startswith": "LIKE %s || '%%%%'", "istartswith": "LIKE UPPER(%s) || '%%%%'"}

    Database = Database

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

        opts = self.settings_dict["OPTIONS"]
        RC = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self.isolation_level = opts.get("isolation_level", RC)

        self.features = DatabaseFeatures(self)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)

    def get_connection_params(self):
        settings_dict = self.settings_dict
        # None may be used to connect to the default 'postgres' db
        if settings_dict["NAME"] == "":
            from django.core.exceptions import ImproperlyConfigured

            raise ImproperlyConfigured("settings.DATABASES is improperly configured. " "Please supply the NAME value.")
        conn_params = {"database": settings_dict["NAME"] or "postgres"}
        conn_params.update(settings_dict["OPTIONS"])
        if "autocommit" in conn_params:
            del conn_params["autocommit"]
        if "isolation_level" in conn_params:
            del conn_params["isolation_level"]
        if settings_dict["USER"]:
            conn_params["user"] = settings_dict["USER"]
        if settings_dict["PASSWORD"]:
            conn_params["password"] = force_str(settings_dict["PASSWORD"])
        if settings_dict["HOST"]:
            conn_params["host"] = settings_dict["HOST"]
        if settings_dict["PORT"]:
            conn_params["port"] = settings_dict["PORT"]
        return conn_params

    def get_new_connection(self, conn_params):
        return Database.connect(**conn_params)

    def init_connection_state(self):
        settings_dict = self.settings_dict
        self.connection.set_client_encoding("UTF8")
        tz = "UTC" if settings.USE_TZ else settings_dict.get("TIME_ZONE")
        if tz:
            try:
                get_parameter_status = self.connection.get_parameter_status
            except AttributeError:
                # psycopg2 < 2.0.12 doesn't have get_parameter_status
                conn_tz = None
            else:
                conn_tz = get_parameter_status("TimeZone")

            if conn_tz != tz:
                cursor = self.connection.cursor()
                try:
                    cursor.execute(self.ops.set_time_zone_sql(), [tz])
                finally:
                    cursor.close()
                # Commit after setting the time zone (see #17062)
                if not self.get_autocommit():
                    self.connection.commit()

    def create_cursor(self):
        cursor = self.connection.cursor()
        cursor.tzinfo_factory = utc_tzinfo_factory if settings.USE_TZ else None
        return cursor

    def _set_isolation_level(self, isolation_level):
        assert isolation_level in range(1, 5)  # Use set_autocommit for level = 0
        if self.psycopg2_version >= (2, 4, 2):
            self.connection.set_session(isolation_level=isolation_level)
        else:
            self.connection.set_isolation_level(isolation_level)

    def _set_autocommit(self, autocommit):
        with self.wrap_database_errors:
#.........这里部分代码省略.........

class pgServerSideCurorDBWrapper(DatabaseWrapper):
    """
    Psycopg2 database backend that allows the use of server side cursors.

    Intented Usage:

    qs = Model.objects.all()
    with server_side_cursors(qs, itersize=x):
        for item in qs.iterator():
            item.value

    """
    vendor = 'postgresql'
    operators = {
        'exact': '= %s',
        'iexact': '= UPPER(%s)',
        'contains': 'LIKE %s',
        'icontains': 'LIKE UPPER(%s)',
        'regex': '~ %s',
        'iregex': '~* %s',
        'gt': '> %s',
        'gte': '>= %s',
        'lt': '< %s',
        'lte': '<= %s',
        'startswith': 'LIKE %s',
        'endswith': 'LIKE %s',
        'istartswith': 'LIKE UPPER(%s)',
        'iendswith': 'LIKE UPPER(%s)',
    }
    
    def __init__(self, *args, **kwargs):
        super(DatabaseWrapper, self).__init__(*args, **kwargs)

        self.features = DatabaseFeatures(self)
        autocommit = self.settings_dict["OPTIONS"].get('autocommit', False)
        self.features.uses_autocommit = autocommit
        if autocommit:
            level = psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
        else:
            level = psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
        self._set_isolation_level(level)
        self.ops = DatabaseOperations(self)
        self.client = DatabaseClient(self)
        self.creation = DatabaseCreation(self)
        self.introspection = DatabaseIntrospection(self)
        self.validation = BaseDatabaseValidation(self)
        self._pg_version = None

    def check_constraints(self, table_names=None):
        """
        To check constraints, we set constraints to immediate. Then, when, we're done we must ensure they
        are returned to deferred.
        """
        self.cursor().execute('SET CONSTRAINTS ALL IMMEDIATE')
        self.cursor().execute('SET CONSTRAINTS ALL DEFERRED')

    def close(self):
        self.validate_thread_sharing()
        if self.connection is None:
            return

        try:
            self.connection.close()
            self.connection = None
        except Database.Error:
            # In some cases (database restart, network connection lost etc...)
            # the connection to the database is lost without giving Django a
            # notification. If we don't set self.connection to None, the error
            # will occur a every request.
            self.connection = None
            logger.warning('psycopg2 error while closing the connection.',
                exc_info=sys.exc_info()
            )
            raise

    def _get_pg_version(self):
        if self._pg_version is None:
            self._pg_version = get_version(self.connection)
        return self._pg_version
    pg_version = property(_get_pg_version)

    def _cursor(self):
        settings_dict = self.settings_dict
        if self.connection is None:
            if settings_dict['NAME'] == '':
                from django.core.exceptions import ImproperlyConfigured
                raise ImproperlyConfigured("You need to specify NAME in your Django settings file.")
            conn_params = {
                'database': settings_dict['NAME'],
            }
            conn_params.update(settings_dict['OPTIONS'])
            if 'autocommit' in conn_params:
                del conn_params['autocommit']
            if settings_dict['USER']:
                conn_params['user'] = settings_dict['USER']
            if settings_dict['PASSWORD']:
                conn_params['password'] = settings_dict['PASSWORD']
            if settings_dict['HOST']:
                conn_params['host'] = settings_dict['HOST']
            if settings_dict['PORT']:
#.........这里部分代码省略.........