Mailer generation and templates in Ruby on Rails - Step-by-Step Execution

Concept Flow - Mailer generation and templates

Generate Mailer with command

↓

Mailer class created

↓

Define mail method with subject, to, from

↓

Create email template file

↓

Render template with variables

↓

Send email via mailer method

↓

Email delivered to recipient

This flow shows how Rails generates a mailer, defines email methods, creates templates, and sends emails.

Execution Sample

Ruby on Rails

rails generate mailer UserMailer

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

This code generates a mailer and defines a welcome_email method that sends an email to a user.

Execution Table

Step	Action	Code/Command	Result/Output
1	Generate mailer	rails generate mailer UserMailer	Creates app/mailers/user_mailer.rb and views/user_mailer/
2	Define mail method	def welcome_email(user)...mail(...)	Method ready to send email with user data
3	Create template	app/views/user_mailer/welcome_email.html.erb	Template file for email body created
4	Call mailer method	UserMailer.welcome_email(user).deliver_now	Email object created and sent
5	Email sent	SMTP server processes email	User receives welcome email
6	Exit	No more mail to send	Process ends

💡 Mailer method called and email sent, no further actions

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
user	nil	User object passed in	User object passed in	User object passed in
@user	nil	User object assigned	User object assigned	User object assigned
mail object	nil	Mail::Message created	Mail::Message sent	Mail::Message sent

Key Moments - 3 Insights

Why do we need to create a template file after defining the mail method?

The mail method sets up the email headers, but the template file contains the actual email content. Without the template, the email body would be empty. See execution_table step 3.

What happens if we forget to call deliver_now or deliver_later on the mailer method?

The email is not sent automatically. The mail method only prepares the email object. Sending happens when deliver_now or deliver_later is called. See execution_table step 4.

How does the mailer know which template to use?

Rails uses the mail method name (like welcome_email) to find the matching template file in views/user_mailer/. See execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the email template file created?

A Step 4

B Step 1

C Step 3

D Step 5

💡 Hint

Check the 'Action' column for template creation in execution_table

According to variable_tracker, what is the state of the mail object after step 4?

A nil

B Mail::Message sent

C User object assigned

D Mail::Message created

💡 Hint

Look at the 'mail object' row and 'After Step 4' column in variable_tracker

If we skip calling deliver_now on the mailer method, what will happen?

A Email will not be sent

B Email will be sent immediately

C Email will be queued for later

D Template will not be rendered

💡 Hint

Refer to key_moments about calling deliver_now or deliver_later

Concept Snapshot

Rails Mailer Generation & Templates:
- Generate mailer: rails generate mailer NameMailer
- Define mail method with mail(to:, subject:)
- Create matching template in views/name_mailer/method.html.erb
- Call mailer.method(args).deliver_now to send
- Template renders email body
- deliver_now triggers immediate send

Full Transcript

This visual execution shows how Rails mailers are generated and used. First, the mailer is created with a command, which sets up the mailer class and folder for templates. Then, a mail method is defined to specify email details like recipient and subject. Next, a template file is created to hold the email content. When the mailer method is called with deliver_now, Rails renders the template and sends the email. Variables like the user and mail object change state through these steps. Key points include the need for templates to provide email content and the requirement to call deliver_now to actually send the email.

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