Action Mailer Coder

Mailer Design Principles

Group Related Emails

class NotificationMailer < ApplicationMailer def comment_reply(user, comment) @user = user @comment = comment mail(to: @user.email, subject: "New reply to your comment") end

def mentioned(user, mention) @user = user @mention = mention mail(to: @user.email, subject: "You were mentioned") end end

Parameterized Mailers

class NotificationMailer < ApplicationMailer before_action { @user = params.fetch(:user) } before_action { @account = params.fetch(:account) }

def comment_reply @comment = params.fetch(:comment) mail(to: @user.email, subject: "New reply on #{@account.name}") end end

Calling the mailer

NotificationMailer.with(user: user, account: account, comment: comment).comment_reply.deliver_later

Dynamic Defaults with Inheritance

class AccountMailer < ApplicationMailer default from: -> { build_from_address } before_action { @account = params.fetch(:account) }

private

def build_from_address @account.custom_email_sender? ? email_address_with_name(@account.custom_email_address, @account.custom_email_name) : email_address_with_name("hello@example.com", @account.name) end end

Background Delivery

UserMailer.with(user: user).welcome.deliver_later # Immediate queue UserMailer.with(user: user).welcome.deliver_later(wait: 1.hour) # Delayed UserMailer.with(user: user).digest.deliver_later(wait_until: Date.tomorrow.morning) # Scheduled

Email Previews

test/mailers/previews/notification_mailer_preview.rb

class NotificationMailerPreview < ActionMailer::Preview def comment_reply NotificationMailer.with( user: User.first, account: Account.first, comment: Comment.first ).comment_reply end end

Access at: http://localhost:3000/rails/mailers

Internationalization

def welcome @user = params.fetch(:user) I18n.with_locale(@user.locale) do mail(to: @user.email, subject: t(".subject", name: @user.name)) end end

Attachments

def invoice(order) attachments.inline["logo.png"] = File.read("app/assets/images/logo.png") attachments["invoice.pdf"] = generate_pdf(order) mail(to: order.email, subject: "Your Invoice ##{order.number}") end

Testing (RSpec)

RSpec.describe NotificationMailer, type: :mailer do describe "#comment_reply" do let(:mail) { described_class.with(user: user, comment: comment).comment_reply }

it "renders the headers" do
  expect(mail.subject).to match(/New reply/)
  expect(mail.to).to eq([user.email])
end

it "delivers later" do
  expect { mail.deliver_later }.to have_enqueued_job(ActionMailer::MailDeliveryJob)
end

end end

Anti-Patterns

Anti-Pattern Problem Solution

One mailer per email Hard to navigate Group related emails

Skipping .with()

Implicit dependencies Use parameterized mailers

deliver_now

Blocks request Use deliver_later

Missing previews Can't visually test Create preview classes

Output Format

When creating mailers, provide:

• Mailer Class - The complete implementation

• Views - HTML and text templates

• Preview - Preview class for visual testing

• Tests - Example test cases