Sessions+draggable element

Hi

I am doing draggable element with sessions. But sessions are new to
me. I have a draggable_element which should be dragged to the cart. I
have defined action add for receving element. How I can delivery
variable or text to the receving element

So my view goes :

<div id="drag_params">
  <p id="param1" class="params" alt="nosc">TEST DRAGGABLE</p>
  <%= draggable_element "param1", :revert => true%>
</div>

<div id="cart" class="cart" style="border:3px solid black; width:
200px; height:200px;">
  <%= render :partial => "cart"%>
  </div>
  <div id="indicator" style="display:none;">
    Params are updating...
  </div>
</div>

<%= drop_receiving_element "cart",
  :update => "drop_params",
  :url => {:action => "add"},
  :accept => "params",
  :hoverclass => "cart-active",
  :loading => "Element.show('indicator')",
  :complete => "Element.hide('indicator')"%>

Contoroller goes :

In controller I have no idea what I should do. I have done few
sessions with php, but not with rails.

def index
    session[:pipe] ||= {}

end
def add

    render :partial => "cart"
end

Partial cart goes:
<% session[:pipe].each do [param]%>
  <div id="drop_params">

  </div>
<% end %>

I priciate for your help

drop_receiving (like most other js helpers of that type)
has a option :with, which allows to add additional information
to the call

:with - A JavaScript expression specifying the parameters for
the XMLHttpRequest. Any expressions should return a valid URL query
string.

In the controller you just store the information you received
You can do that in the session (which basically is just a hash)
or in a db table.

I didn't get it work. Can you give me a sample for function :with, how
I can store information.