Python django.db.models 模块，Expression() 实例源码

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def get(self, key, default=None, version=None):
        key = self.make_key(key, version=version)
        self.validate_key(key)
        db = router.db_for_read(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT cache_key, value, expires FROM %s "
                           "WHERE cache_key = %%s" % table, [key])
            row = cursor.fetchone()
        if row is None:
            return default

        expires = row[2]
        expression = models.Expression(output_field=models.DateTimeField())
        for converter in (connection.ops.get_db_converters(expression) +
                          expression.get_db_converters(connection)):
            expires = converter(expires, expression, connection, {})

        if expires < timezone.now():
            db = router.db_for_write(self.cache_model_class)
            connection = connections[db]
            with connection.cursor() as cursor:
                cursor.execute("DELETE FROM %s "
                               "WHERE cache_key = %%s" % table, [key])
            return default

        value = connection.ops.process_clob(row[1])
        return pickle.loads(base64.b64decode(force_bytes(value)))

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True

def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
        timeout = self.get_backend_timeout(timeout)
        db = router.db_for_write(self.cache_model_class)
        connection = connections[db]
        table = connection.ops.quote_name(self._table)

        with connection.cursor() as cursor:
            cursor.execute("SELECT COUNT(*) FROM %s" % table)
            num = cursor.fetchone()[0]
            now = timezone.now()
            now = now.replace(microsecond=0)
            if timeout is None:
                exp = datetime.max
            elif settings.USE_TZ:
                exp = datetime.utcfromtimestamp(timeout)
            else:
                exp = datetime.fromtimestamp(timeout)
            exp = exp.replace(microsecond=0)
            if num > self._max_entries:
                self._cull(db, cursor, now)
            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
            b64encoded = base64.b64encode(pickled)
            # The DB column is expecting a string, so make sure the value is a
            # string, not bytes. Refs #19274.
            if six.PY3:
                b64encoded = b64encoded.decode('latin1')
            try:
                # Note: typecasting for datetimes is needed by some 3rd party
                # database backends. All core backends work without typecasting,
                # so be careful about changes here - test suite will NOT pick
                # regressions.
                with transaction.atomic(using=db):
                    cursor.execute("SELECT cache_key, expires FROM %s "
                                   "WHERE cache_key = %%s" % table, [key])
                    result = cursor.fetchone()

                    if result:
                        current_expires = result[1]
                        expression = models.Expression(output_field=models.DateTimeField())
                        for converter in (connection.ops.get_db_converters(expression) +
                                          expression.get_db_converters(connection)):
                            current_expires = converter(current_expires, expression, connection, {})

                    exp = connection.ops.adapt_datetimefield_value(exp)
                    if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
                        cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
                                       "WHERE cache_key = %%s" % table,
                                       [b64encoded, exp, key])
                    else:
                        cursor.execute("INSERT INTO %s (cache_key, value, expires) "
                                       "VALUES (%%s, %%s, %%s)" % table,
                                       [key, b64encoded, exp])
            except DatabaseError:
                # To be threadsafe, updates/inserts are allowed to fail silently
                return False
            else:
                return True