record is not store in DB & session.delete('key') not workin

Hi,

I'm creating multi page form (wizard like pages) in my application using
code at

http://snippets.dzone.com/posts/show/277#related

problem ===> When I create a new coupon first time, it is stored in DB.
After saving I try to clear out(delete old session in which coupon
object is stored) session using session.delete('partial_coupon') But
session is not get clear and also coupon object is not get store in DB.

Please tell me what went wrong?

Following is controller code---->
class CouponsController < ApplicationController
     before_filter :get_partial_coupon_from_session, :only =>
[:business_coupon]
     after_filter :save_partial_coupon_in_session, :only =>
[:business_coupon]

def business_coupon
    case request.method
      when :post
        @current_stage = params['current_stage']
        if @current_stage == "stage1"
          @coupon.attributes = {:title => params[:coupon][:title]}
          if valid_for_attributes(@coupon,["title"])
            @current_stage = "stage2"
          end
        elsif @current_stage == "stage2"
          @coupon.attributes = {:tag_line => params[:coupon][:tag_line]}
          if valid_for_attributes(@coupon,["tag_line"])
            @current_stage = "stage3"
          end
        elsif @current_stage == "stage3"
          @coupon.attributes = {:price => params[:coupon][:price]}
          if @coupon.save

   ##### HERE I TRY TO CLEAR SESSION DATA
            session.delete('partial_coupon')
            flash['notice'] = "Coupon successfully created."
            render :action => "show", :id => @coupon
          else
       flash[:error] = "Could not save coupon
#{@coupon.errors.full_messages().join(', ')}"
          end

        end
      when :get
        @current_stage = "stage1"
    end

  end

private
    def get_partial_coupon_from_session
      unless session['partial_coupon'].nil?
        @coupon = session['partial_coupon']
      else
        @coupon = Coupon.new
      end
    end

    def save_partial_coupon_in_session
      unless @coupon.nil?
        session['partial_coupon'] = @coupon
      end
    end

def valid_for_attributes( model, attributes )
      unless model.valid?
        errors = model.errors
        our_errors = Array.new
        errors.each { |attr,error|
          if attributes.include? attr
            our_errors << [attr,error]
          end
        }
        errors.clear
        our_errors.each { |attr,error| errors.add(attr,error) }
        return false unless errors.empty?
      end
      return true
end

def clear_stage_errors
      unless session['partial_coupon'].nil?
        session['partial_coupon'].errors.clear
      end
end
end

############### VIEWS #############3
new.html.erb

<h1>New coupon</h1>

<% form_for(@coupon) do |f| %>
  <%= hidden_field_tag "current_stage", "#{@current_stage}"%>
  <%= f.error_messages %>

<%= render :partial => "coupons/#{@current_stage}", :locals => {:f => f}
%>

<% end %>
<%= link_to 'Back', coupons_path %>