'Sets up the persistence layer ready for use.
:param working_directory: Path to the working directory
that will contain the the db at working directory/DATABASE_PATH
:param db_name: The name of the database'

def __init__(self, working_directory, db_name):

    db_path = os.path.join(working_directory, os.path.join(DATABASE_DIRECTORY, (u'%s.db' % db_name)))
    super(TrustChainDB, self).__init__(db_path)
    self._logger.debug('TrustChain    database    path:    %s', db_path)
    self.db_name = db_name
    self.open()
