Mailer generation and templates in Ruby on Rails

Introduction

Mailers help your app send emails automatically. Templates let you design what those emails look like.

Send a welcome email when a user signs up.

Notify users about password changes.

Send order confirmations after a purchase.

Alert admins about important events.

Send newsletters or updates to users.

Syntax

Ruby on Rails

rails generate mailer MailerName method_name

# Example:
rails generate mailer UserMailer welcome_email

The command creates a mailer class and email templates.

Mailer methods define what emails to send and what data to include.

Examples

This mailer sends a welcome email to a user.

Ruby on Rails

class UserMailer < ApplicationMailer
  def welcome_email(user)
    @user = user
    mail(to: @user.email, subject: 'Welcome!')
  end
end

This is the HTML email template that uses the user name.

Ruby on Rails

# Template: app/views/user_mailer/welcome_email.html.erb
<h1>Hello, <%= @user.name %>!</h1>
<p>Thanks for joining us.</p>

This is the plain text version of the email for simpler email clients.

Ruby on Rails

# Template: app/views/user_mailer/welcome_email.text.erb
Hello, <%= @user.name %>!
Thanks for joining us.

Sample Program

This example shows a mailer sending a welcome email to a user named Alice. It prints the recipient, subject, and email body.

Ruby on Rails

class UserMailer < ApplicationMailer
  def welcome_email(user)
    @user = user
    mail(to: @user.email, subject: 'Welcome to Our App')
  end
end

# Template: app/views/user_mailer/welcome_email.html.erb
# <h1>Welcome, <%= @user.name %>!</h1>
# <p>We are happy you joined.</p>

# Usage in controller or console:
user = OpenStruct.new(name: 'Alice', email: '[e-mail]')
email = UserMailer.welcome_email(user)
puts email.to
puts email.subject
puts email.body.encoded

Important Notes

Always create both HTML and plain text templates for better email compatibility.

Use instance variables (like @user) to pass data to templates.

Test emails in development using tools like Letter Opener or Mailcatcher.

Summary

Mailers send emails from your Rails app.

Templates define how emails look in HTML and text.

Generate mailers with Rails commands and customize methods and views.

Practice

1. What is the primary purpose of a mailer in a Rails application?

easy

A. To send emails from the application

B. To handle database migrations

C. To manage user sessions

D. To style HTML templates

Solution

1. Step 1: Understand the role of mailers

   Mailers in Rails are designed to send emails from the application to users or other recipients.

2. Step 2: Differentiate from other components

   Database migrations handle schema changes, sessions manage user logins, and styling is done in views or CSS, not mailers.

3. Final Answer:

   To send emails from the application -> Option A

4. Quick Check:

   Mailer = send emails [OK]

Hint: Mailers send emails, not handle data or styling [OK]

Common Mistakes:

• Confusing mailers with controllers
• Thinking mailers manage database
• Assuming mailers style HTML

2. Which Rails command correctly generates a mailer named UserMailer?

easy

A. rails generate controller UserMailer

B. rails generate mailer UserMailer

C. rails generate model UserMailer

D. rails generate job UserMailer

Solution

1. Step 1: Identify the correct generator for mailers

   The command rails generate mailer UserMailer creates a mailer class and related files.

2. Step 2: Understand other generators

   Controllers handle web requests, models handle data, and jobs handle background tasks, so those commands are incorrect for mailers.

3. Final Answer:

   rails generate mailer UserMailer -> Option B

4. Quick Check:

   Mailer generator uses 'mailer' keyword [OK]

Hint: Use 'rails generate mailer' to create mailers [OK]

Common Mistakes:

• Using controller generator for mailers
• Confusing model and mailer generators
• Typing job instead of mailer

3. Given this mailer method:

class UserMailer < ApplicationMailer
  def welcome_email(user)
    @user = user
    mail(to: @user.email, subject: 'Welcome!')
  end
end

What happens when UserMailer.welcome_email(@user).deliver_now is called?

medium

A. The email is queued but not sent immediately

B. The method returns a string with the email content but does not send it

C. An email is sent immediately to the user's email with subject 'Welcome!'

D. An error occurs because deliver_now is not a valid method

Solution

1. Step 1: Understand mailer method behavior

   The method welcome_email sets instance variables and calls mail to prepare the email.

2. Step 2: Effect of deliver_now

   Calling deliver_now sends the email immediately instead of queuing it.

3. Final Answer:

   An email is sent immediately to the user's email with subject 'Welcome!' -> Option C

4. Quick Check:

   deliver_now sends email immediately [OK]

Hint: deliver_now sends email immediately, deliver_later queues it [OK]

Common Mistakes:

• Thinking deliver_now only prepares email
• Confusing deliver_now with deliver_later
• Assuming deliver_now is invalid

4. Identify the error in this mailer template file named welcome_email.html.erb:

<h1>Welcome, <%= @user.name %>!</h1>
<p>Thanks for joining.</p>
<p>Your email is: <%= user.email %></p>

medium

A. The = sign is missing in the ERB tags

B. The HTML tags are incorrect and will cause rendering errors

C. The template file should be named welcome_email.text.erb

D. The variable user is undefined; should use @user

Solution

1. Step 1: Check variable usage in template

   The mailer method sets @user, so the template must use @user to access user data.

2. Step 2: Identify incorrect variable

   The template uses user.email which is undefined, causing an error.

3. Final Answer:

   The variable user is undefined; should use @user -> Option D

4. Quick Check:

   Use instance variables (@user) in mailer templates [OK]

Hint: Mailer templates use instance vars like @user, not local vars [OK]

Common Mistakes:

• Using local variables instead of instance variables
• Misnaming template files
• Forgetting <%= in ERB tags

5. You want to send a welcome email with both HTML and plain text versions. Which setup correctly supports this in Rails mailers?

hard

A. Create welcome_email.html.erb and welcome_email.text.erb templates in the mailer views folder

B. Create only welcome_email.html.erb template; Rails auto-generates text version

C. Create welcome_email.erb with mixed HTML and text content

D. Create welcome_email.text.erb only; HTML is optional

Solution

1. Step 1: Understand multi-format email templates

   Rails supports sending emails with both HTML and plain text by providing separate templates named with .html.erb and .text.erb extensions.

2. Step 2: Why both templates are needed

   Some email clients prefer plain text, so having both ensures compatibility and better user experience.

3. Final Answer:

   Create welcome_email.html.erb and welcome_email.text.erb templates in the mailer views folder -> Option A

4. Quick Check:

   Both .html.erb and .text.erb templates needed for multi-format emails [OK]

Hint: Use both .html.erb and .text.erb templates for emails [OK]

Common Mistakes:

• Assuming Rails auto-generates text version
• Mixing HTML and text in one template
• Skipping plain text template