20140331025708_create_cashes.rb

class CreateCashes < ActiveRecord::Migration
  def change
    create_table :cashes do |t|
      t.datetime :start_at
      t.datetime :end_at
      t.decimal :value_open
      t.decimal :value_phisic_closed
      t.decimal :value_system_closed

      t.timestamps
    end
  end
end

_form.html.erb

<%= simple_form_for @cash do |f| %>
<div class="form-group">
	<%= f.input :value_open, :input_html =>{:class=>"form-control"} %>
</div>
<%= button_tag(type: :submit, :class=>"btn btn-success") do %>
   <i class="icon-save"></i> Registar abertura de caixa
<% end %>
<% end %>

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :authenticate_user!
  before_filter :authenticate_cash

  def after_sign_in_path_for(resource)
     new_cash_path
  end

  def authenticate_cash
    redirect_to new_cah_path if session[:cash_id].nil?
  end
end

cashes_controller.rb

class CashesController < ApplicationController
	

	def index
		start_at = current_user.current_sign_in_at
		@billings = Billing.where("created_at>?",start_at)
	end

	def new
		@cash = Cash.new
	end

	def create
		@cash = Cash.new(cash_params)
		@cash.start_at = current_user.current_sign_in_at
		if @cash.save
			session[:cash_id] = @cash.id
			redirect_to root_url
		end
	end



	def cash_params
		params.require(:cash).permit(:value_open, :value_phisic_closed, :value_system_closed)
	end


end

cashing.rb

class Cashing < ActiveRecord::Base
end