ruby-on-rails – Action Mailer附件的未定义方法URL

ActionView::Template::Error (undefined method `url' for nil:NilClass)

我有这个附件正在增加零

<%= image_tag attachments['tippedlogods.png'].url %>

话虽这么说,我已经在方法中声明了发送电子邮件的附件,这里：

def confirmation(order)
    @order = order
    mail(to: @order.email,subject: "Order Confirmation",content_type: "text/html")
    attachments.inline['tippedlogods.png'] = File.read("app/assets/images/tippedlogods.png")
  end

在我的production.rb中：

config.action_mailer.raise_delivery_errors = true
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.default_url_options = { :host => 'hidden-peak-xxxx.heroku.com',:only_path => false}
  config.action_mailer.asset_host = 'hidden-peak-xxxx.heroku.com'
  ActionMailer::Base.smtp_settings = {
  :address    => "smtp.sendgrid.net",:port       => 587,:user_name  => ENV['SENDGRID_USERNAME'],:password   => ENV['SENDGRID_PASSWORD'],:domain     => ENV['SENDGRID_DOMAIN'],:authentication  => :plain
  }

这不是在确认电子邮件中发送图像的方法吗？

我正在关注RoR Guides here ……

注意Rails 4~