在我的Rails应用程序中，我尝试将发票附加到电子邮件中:definvoice(invoice)attachment:content_disposition=>"attachment",:body=>InvoicePdf.new(invoice),:content_type=>"application/pdf",:filename=>'invoice.pdf'mail(:to=>@user.email,:subject=>"YourInvoice")endInvoicePdf是一个PrawnPDF文档:classInvoicePdf我在电子邮件中没有收到附件。我究竟做错了什么？任何提示