如何在调用render_to_string呈现模板时使Rails辅助方法可用

我有一个ActiveMailer类,在里面我使用render_to_string方法发送附带PDF模板的电子邮件,如下所示:

 def send_sales_order(email_service)
    @email_service = email_service
    @sales_order = SalesOrder.find_by_cid(email_service.order[:id])
    mail(:subject => I18n.t("custom_mailer.sales_order.subject", company_name: "test"), :to => @email_service.recipients) do |format|
      format.html
      format.pdf do
        attachments['purchase_order.pdf'] = WickedPdf.new.pdf_from_string(
          render_to_string('sales_orders/show.pdf.erb', locals: {current_company: @sales_order.company})
        )
      end
    end
  end

在show.pdf.erb模板中,我调用了我在其他地方定义的辅助方法,例如在ApplicationController中定义的current_company方法,如下所示:

    class ApplicationController < ActionController::Base
      helper_method :current_company, :current_role

      def current_company
        return if current_user.nil?
        if session[:current_company_id].blank?
          session[:current_company_id] = current_user.companies.first.id.to_s
        end
        @current_company ||= Company.find(session[:current_company_id])
      end

但是当我使用render_to_string方法渲染模板时,这些辅助方法不可用,有没有办法解决这个问题？

谢谢