code: def update_port_precommit(self, context):
          
          vlan_segment, vxlan_segment = self._get_segments(
              context.top_bound_segment, context.bottom_bound_segment)
          orig_vlan_segment, orig_vxlan_segment = self._get_segments(
              context.original_top_bound_segment,
              context.original_bottom_bound_segment)
  
          if (self._is_vm_migrating(context, vlan_segment, orig_vlan_segment) or
              self._is_status_down(context.current)):
              vni = (self._port_action_vxlan(
                  context.original, orig_vxlan_segment, self._delete_nve_db)
                  if orig_vxlan_segment else 0)
              self._port_action_vlan(context.original, orig_vlan_segment,
                                     self._delete_nxos_db, vni)
          elif self._is_supported_deviceowner(context.current):
              vni = self._port_action_vxlan(context.current, vxlan_segment,
                          self._configure_nve_db) if vxlan_segment else 0
              self._port_action_vlan(context.current, vlan_segment,
                                     self._configure_nxos_db, vni)
docs: Update port pre-database transaction commit event.