ActiveMailer PDF Email Attachments with Paperclip

Let's say we have a Report model, which has PDFs as Paperclip attachments:

# /app/models/report.rb
class Report < ActiveRecord::Base
  belongs_to :user
  has_attached_file :pdf
  validates_attachment :pdf, content_type: { content_type: "application/pdf" }
end

We want to automate sending out a report by email each week to the user who created the report (this post won't cover the automation; use something to automate that, like a CRON job, or the Clockwork gem).

For this example, I've set up an ActionMailer mailer to send the email, and an ActiveJob job to generate the PDF from values in the Report object.

Creating the ActiveJob job

rails g job generateReportPdf

# /app/jobs/generate_report_pdf_job.rb
class GenerateReportPdfJob < ActiveJob::Base
  queue_as :default

  def perform(args)
    @report = Report.find args[:report_id]
    # create an instance of ActionView, so we can use the render method outside of a controller
    av = ActionView::Base.new()
    av.view_paths = ActionController::Base.view_paths

    # need these in case your view constructs any links or references any helper methods.
    av.class_eval do
      include Rails.application.routes.url_helpers
      include ApplicationHelper
    end

    pdf_html = av.render template: 'reports/generate_pdf', layout: 'layouts/pdf', locals: {report: @report}

    # use wicked_pdf gem to create PDF from the doc HTML
    doc_pdf = WickedPdf.new.pdf_from_string(
      pdf_html,
      page_size: 'Letter',
      javascript_delay: 6000
    )

    # save PDF to disk
    pdf_path = Rails.root.join('tmp/reports', "#{@report.id}_#{Date.today.iso8601}.pdf")
    File.open(pdf_path, 'wb') do |file|
      file << doc_pdf
    end

    @report.pdf = File.open pdf_path
    @report.save!

    # The report has now been saved elsewhere using Paperclip; we don't need to store it locally
    File.delete(pdf_path) if File.exist?(pdf_path)

Creating the ActionMailer mailer

Now we create the mailer which will call out to this ActiveJob job to generate the PDF:

rails g mailer reportPdf

# /app/mailers/report_pdf.rb
class ReportPdf < ApplicationMailer
  def send_mail(report_id:)
    @report = Report.find report_id

    GeneratePdfJob.perform_now(report_id: @report.id)
    @report.reload

    attachments["report_#{Date.today.iso8601}.pdf"] = {
      mime_type: 'application/pdf',
      content: open(@report.pdf.expiring_url).read
    }

    mail(
      to: @report.user.email,
      subject: "Weekly PDF Email: #{Date.today.iso8601}",
    )
  end
end

So now all we need to do is call ReportPdf.send_mail(report_id: @report.id) to generate and send an email with a PDF attachment, powered by Paperclip. The PDF generation is done via the wicked_pdf gem.