Cannot save tag_list when using multi-step forms

Question

I have a belonging model that allows user to post objects to be sold or rented on my website. I recently changed the form, making it a multi-step form: a first form asks the name of the object and if the object is for sale or to rent, a second form ask for object's details, with the fields depending on the user's choice.

I am using is_taggable, with Rails 3.0.5, and my problem is that tag_list is never saved in the database since I switched to the multi-step form (all the other fields are saved correctly).

I followed Ryan Bates Rails cast #217.

Before, I was using: @belonging.tag_list = params[:belonging][:tag_list]

Since I went from multistep, I am using: @belonging.tag_list = session[:belonging_params][:tag_list]

I am a bit of a newbie in Rails, so there might be something obvious I am missing here. I spent the whole afternoon and evening trying to understand what is wrong, any help will therefore be appreciated!

Here are the 'new' and 'create' action of my controller:

class BelongingsController < ApplicationController
  before_filter :authenticate_user!, :except => [:index, :with_tag, :remove_tag]
  after_filter :update_tag_cloud, :only => [:create, :update]

  def new
    @title = "Insert a new product or service"
    @user = current_user
    session[:belonging_params] ||= {}
    session[:belonging_step] = nil
    @belonging = @user.belongings.new(session[:belonging_params])
    session[:belonging_params][:tag_list] ||= []
    @belonging.current_step = session[:belonging_step]
    render 'new'
  end

  def create
    session[:belonging_params].deep_merge!(params[:belonging]) if params[:belonging]
    @belonging = current_user.belongings.build(session[:belonging_params])
    @belonging.current_step = session[:belonging_step]
    @belonging.tag_list=session[:belonging_params][:tag_list]
    if params[:previous_button]
      @belonging.previous_step
      render 'new'
    elsif params[:cancel_button]
      session[:belonging_step] = session[:belonging_params] = nil
      redirect_to user_path(current_user)
    elsif params[:continue_button]
      if @belonging.last_step?
        if @belonging.save!
          expire_fragment('category_list')
          flash[:success] = "New product or service created!"
          session[:belonging_step] = session[:belonging_params] = nil
          redirect_to belonging_path(@belonging)
        else
          flash[:error] = "Object could not be saved"
          render 'new'
        end
      else
        @belonging.next_step
        render 'new'
      end
    else
      render 'new'
    end
    session[:belonging_step] = @belonging.current_step
  end

Many many thanks for any clue !!

Answer 1

I actually thought that:

session[:belonging_params].deep_merge!(params[:belonging]) if params[:belonging]

would copy everything inside params[:belonging] but it seems that params[:belonging][:tag_list] was not copied into session[:belonging_params][:tag_list] as I expected ...

So the problem was solved by adding in the 'create' action a new session variable:

session[:tag_list] = params[:belonging][:tag_list] to be able to save :tag_list from a step of the form to the next.

session[:tag_list] is defined first in the 'new' action as:

session[:tag_list] ||= []