[Rails] updating database on show

[Jens-Christian Fischer]

I'm trying to have an application that models a number of rooms and a  
number of people that can move between the rooms.

The models are like this:

Room:
class Room < ActiveRecord::Base
   has_many :people
end

Person:
class Person < ActiveRecord::Base
   belongs_to :room
   [...]
end

I display a room with links to all linked rooms (/room/show/2,  
room/show/4,...)

Now I want the current person (as in the session object) to "know" which  
room he's in. I tried the following in my room controller:

   def show
     room_id = @params["id"]
     @room = Room.find( room_id )
     if !@session["current_room_id"]
       @session["current_room_id"] = room_id
     end
     person = @session["person"]
     person.room = Room.find( @session["current_room_id"] )
     person.save
   end

but that doesn't seem to work...

I thought about adding a "move" action that moves to a new room, but I'm  
not sure how I can extract the new room id

Any ideas?
thanks
jc