Automatically filling in form field

Summary

Trying to automatically fill in a form field based on the first selected item from a list

Content

Super newbie question!

i have an application with several business Objects. 

Client.floor.room.spot.items at spot

I’ve set up the relationships between them and that’s working great.  I have a page where I select a “client” from a list and that automatically then filters another list just to the right populated by that clients “floors” and so on.  

I created a variable that is persistent for a session with the selected client. (And then one for each of the business Objects).