python logging to database

Question

I'm seeking a way to let the python logger module to log to database and falls back to file system when the db is down.

So basically 2 things: How to let the logger log to database and how to make it fall to file logging when the db is down.

Answer 1

I recently managed to write my own database logger in Python. Since I couldn't find any example I thought I post mine here. Works with MS SQL.

Database table could look like this:

CREATE TABLE [db_name].[log](
    [id] [bigint] IDENTITY(1,1) NOT NULL,
    [log_level] [int] NULL,
    [log_levelname] [char](32) NULL,
    [log] [char](2048) NOT NULL,
    [created_at] [datetime2](7) NOT NULL,
    [created_by] [char](32) NOT NULL,
) ON [PRIMARY]

The class itself:

class LogDBHandler(logging.Handler):
    '''
    Customized logging handler that puts logs to the database.
    pymssql required
    '''
    def __init__(self, sql_conn, sql_cursor, db_tbl_log):
        logging.Handler.__init__(self)
        self.sql_cursor = sql_cursor
        self.sql_conn = sql_conn
        self.db_tbl_log = db_tbl_log

    def emit(self, record):
        # Set current time
        tm = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime(record.created))
        # Clear the log message so it can be put to db via sql (escape quotes)
        self.log_msg = record.msg
        self.log_msg = self.log_msg.strip()
        self.log_msg = self.log_msg.replace(''', '''')
        # Make the SQL insert
        sql = 'INSERT INTO ' + self.db_tbl_log + ' (log_level, ' + 
            'log_levelname, log, created_at, created_by) ' + 
            'VALUES (' + 
            ''   + str(record.levelno) + ', ' + 
            ''' + str(record.levelname) + '', ' + 
            ''' + str(self.log_msg) + '', ' + 
            '(convert(datetime2(7), '' + tm + '')), ' + 
            ''' + str(record.name) + '')'
        try:
            self.sql_cursor.execute(sql)
            self.sql_conn.commit()
        # If error - print it out on screen. Since DB is not working - there's
        # no point making a log about it to the database :)
        except pymssql.Error as e:
            print sql
            print 'CRITICAL DB ERROR! Logging to database not possible!'

And usage example:

import pymssql
import time
import logging

db_server = 'servername'
db_user = 'db_user'
db_password = 'db_pass'
db_dbname = 'db_name'
db_tbl_log = 'log'

log_file_path = 'C:\Users\Yourname\Desktop\test_log.txt'
log_error_level     = 'DEBUG'       # LOG error level (file)
log_to_db = True                    # LOG to database?

class LogDBHandler(logging.Handler):
    [...]

# Main settings for the database logging use
if (log_to_db):
    # Make the connection to database for the logger
    log_conn = pymssql.connect(db_server, db_user, db_password, db_dbname, 30)
    log_cursor = log_conn.cursor()
    logdb = LogDBHandler(log_conn, log_cursor, db_tbl_log)

# Set logger
logging.basicConfig(filename=log_file_path)

# Set db handler for root logger
if (log_to_db):
    logging.getLogger('').addHandler(logdb)
# Register MY_LOGGER
log = logging.getLogger('MY_LOGGER')
log.setLevel(log_error_level)

# Example variable
test_var = 'This is test message'

# Log the variable contents as an error
log.error('This error occurred: %s' % test_var)

Above will log both to the database and to the file. If file is not needed - skip the 'logging.basicConfig(filename=log_file_path)' line. Everything logged using 'log' - will be logged as MY_LOGGER. If some external error appears (i.e. in the module imported or something) - error will appear as 'root', since 'root' logger is also active, and is using the database handler.