<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_update_topology_db(self, **params):
 """Add or update an entry to the topology DB. """

        topo_dict = params.get('columns')
        session = db.get_session()
        host = topo_dict.get('host')
        protocol_interface = topo_dict.get('protocol_interface')
        with session.begin(subtransactions=True):
            try:
                # Check if entry exists.
                session.query(DfaTopologyDb).filter_by(
                    host=host, protocol_interface=protocol_interface).one()
                session.query(DfaTopologyDb).filter_by(
                    host=host, protocol_interface=protocol_interface).update(
                    topo_dict)
            except orm_exc.NoResultFound:
                LOG.info("Creating new topology entry for host "
                         "%(host)s on Interface %(intf)s",
                         {'host': host, 'intf': protocol_interface})
                topo_disc = DfaTopologyDb(
                    host=host, protocol_interface=protocol_interface,
                    phy_interface=topo_dict.get('phy_interface'),
                    created=topo_dict.get('created'),
                    heartbeat=topo_dict.get('heartbeat'),
                    remote_mgmt_addr=topo_dict.get('remote_mgmt_addr'),
                    remote_system_name=topo_dict.get('remote_system_name'),
                    remote_system_desc=topo_dict.get('remote_system_desc'),
                    remote_port_id_mac=topo_dict.get('remote_port_id_mac'),
                    remote_chassis_id_mac=topo_dict.get(
                        'remote_chassis_id_mac'),
                    remote_port=topo_dict.get('remote_port'),
                    remote_evb_cfgd=topo_dict.get('remote_evb_cfgd'),
                    remote_evb_mode=topo_dict.get('remote_evb_mode'),
                    configurations=topo_dict.get('configurations'))
                session.add(topo_disc)
            except orm_exc.MultipleResultsFound:
                LOG.error("More than one enty found for agent %(host)s."
                          "Interface %(intf)s",
                          {'host': host, 'intf': protocol_interface})
            except Exception as exc:
                LOG.error("Exception in add_update_topology_db %s", exc)