How to get userdata from some field in db for treeconnector

Hello All,
Sorry iam a newbie for use dhtmlx, i just try to using tree connecor and i want to set link at node in my tree with the userdata in connector, but i don’t know how to get userdata from some field in my table. Anybody can show me how to do this?

Iam already trying to using extra field, but my connector do not show the extra field in xml file. This is result of my xml :

I need to customize my xml to :

Thanks before.

To add userdata you need to use beforeRender event on server side, from which you need to call something like

data.set_userdata(data.get_value(field_id)) … event.html … etuserdata

Thanks a lot Stanislav,
i do what your say and i can set the userdata like as i want before.