module Spree
  module Admin
    class ReturnAuthorizationsController < ResourceController
      belongs_to :order, :find_by => :number

      update.after :associate_inventory_units
      create.after :associate_inventory_units

      def fire
        @return_authorization.send("#{params[:e]}!")
        flash.notice = t('return_authorization_updated')
        respond_with(@return_authorization) { |format| format.html { redirect_to :back } }
      end

      protected
        def associate_inventory_units
          params[:return_quantity].each { |variant_id, qty| @return_authorization.add_variant(variant_id.to_i, qty.to_i) }
        end
    end
  end
end

module Spree
  module Admin
    class ReturnAuthorizationsController < ResourceController
      belongs_to 'spree/order', :find_by => :number

      update.after :associate_inventory_units
      create.after :associate_inventory_units

      def fire
        @return_authorization.send("#{params[:e]}!")
        flash.notice = t('return_authorization_updated')
        respond_with(@return_authorization) { |format| format.html { redirect_to :back } }
      end

      protected
        def associate_inventory_units
          params[:return_quantity].each { |variant_id, qty| @return_authorization.add_variant(variant_id.to_i, qty.to_i) }
        end
    end
  end
end

Correct reference to order model in ReturnAuthorizationsController
Correct reference to order model in ReturnAuthorizationsController
