Email previews in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of email previews in Rails?

Email previews let you see how your emails will look in a browser before sending them. This helps catch mistakes and design issues early.

beginner

Where do you place email preview files in a Rails app?

Email preview files go in the test/mailers/previews folder by default. Rails uses these to show previews in the browser.

beginner

How do you access email previews in a Rails development environment?

You open http://localhost:3000/rails/mailers in your browser to see a list of email previews.

intermediate

How do you define a preview method inside a preview class?

Inside the preview class, define a method that returns the mailer method call with sample data. For example: def welcome_email; UserMailer.welcome_email(User.first); end

beginner

Why is it helpful to use email previews during development?

Email previews save time by letting you check email content and layout without sending real emails. This avoids spamming users and speeds up design fixes.

Where do Rails email previews live by default?

A config/mailers

B app/mailers/previews

C app/views/mailers

D test/mailers/previews

Rails expects email preview files in the test/mailers/previews folder.

How do you view email previews in Rails development?

A Check logs/mail_preview.log

B Visit /rails/mailers in the browser

C Run rails email:preview command

D Use rails console to call preview methods

You open http://localhost:3000/rails/mailers to see previews.

What does an email preview method return?

A A mailer method call that returns a Mail::Message

B A string with email content

C A JSON object with email data

D A plain text file

The preview method calls a mailer method which returns a Mail::Message object.

Why should you use email previews instead of sending test emails?

A Previews are faster and avoid spamming real inboxes

B Previews automatically send emails to all users

C Previews encrypt emails for security

D Previews only work in production

Previews let you check emails quickly without sending real emails.

Which Rails class do you create to define email previews?

A MailerPreview

B EmailPreviewer

C ActionMailer::Preview

D PreviewMailer

Email preview classes inherit from ActionMailer::Preview.

Explain how to set up and use email previews in a Rails app.

Think about where files go, what classes to use, and how to see previews.

Describe the benefits of using email previews during Rails development.

Consider how previews save time and prevent mistakes.

Practice

1. What is the main purpose of email previews in Rails?

easy

A. To view the email content in the browser before sending

B. To send emails automatically to users

C. To store emails in the database

D. To encrypt email content for security

Solution

1. Step 1: Understand the role of email previews

   Email previews allow developers to see how emails will look before sending them out.

2. Step 2: Compare options with this purpose

   Only To view the email content in the browser before sending describes viewing email content in the browser, which matches the purpose of previews.

3. Final Answer:

   To view the email content in the browser before sending -> Option A

4. Quick Check:

   Email previews = View email before sending [OK]

Hint: Email previews show email content before sending [OK]

Common Mistakes:

• Confusing previews with sending emails
• Thinking previews store emails permanently
• Assuming previews encrypt emails

2. Which of the following is the correct way to define a preview method in a Rails mailer preview class?

easy

A. def welcome_email; UserMailer.welcome_email(User.first); end

B. def welcome_email() UserMailer.welcome_email(User.first) end

C. def welcome_email { UserMailer.welcome_email(User.first) }

D. def welcome_email -> UserMailer.welcome_email(User.first)

Solution

1. Step 1: Recall Ruby method syntax in classes

   Methods are defined with def method_name; ...; end syntax.

2. Step 2: Check each option's syntax

   def welcome_email; UserMailer.welcome_email(User.first); end uses correct Ruby method syntax with semicolons and end. Options A, C, and D have syntax errors or invalid Ruby syntax.

3. Final Answer:

   def welcome_email; UserMailer.welcome_email(User.first); end -> Option A

4. Quick Check:

   Correct Ruby method syntax = def welcome_email; UserMailer.welcome_email(User.first); end [OK]

Hint: Use def ...; ...; end for methods in Ruby classes [OK]

Common Mistakes:

• Omitting 'end' keyword
• Using braces {} instead of def/end
• Using arrow syntax which is invalid here

3. Given this preview method in UserMailerPreview:

def notification_email
  UserMailer.notification_email(User.find(1))
end

What will happen when you visit /rails/mailers/user_mailer/notification_email in the browser?

medium

A. An error occurs because UserMailerPreview is missing

B. The email content for user with ID 1 is displayed in the browser

C. The email is sent to user with ID 1 automatically

D. The browser shows a 404 Not Found error

Solution

1. Step 1: Understand what preview methods do

   Preview methods return mail objects that Rails renders as HTML in the browser for preview.

2. Step 2: Analyze the URL and method

   The URL matches the preview method name and class, so Rails will render the email content for user ID 1.

3. Final Answer:

   The email content for user with ID 1 is displayed in the browser -> Option B

4. Quick Check:

   Preview URL shows email content = The email content for user with ID 1 is displayed in the browser [OK]

Hint: Preview URL shows email content, not send email [OK]

Common Mistakes:

• Thinking preview sends email
• Assuming missing preview class error
• Expecting 404 if preview is defined

4. You wrote this preview method:

def alert_email
  UserMailer.alert_email(user)
end

But visiting the preview URL gives an error: undefined local variable or method `user'. What is the fix?

medium

A. Add @user as an instance variable outside the method

B. Change method name to user_alert_email

C. Remove the method and call UserMailer directly

D. Define the variable user inside the method before calling UserMailer

Solution

1. Step 1: Identify cause of error

   The error says user is undefined, meaning it was never assigned a value.

2. Step 2: Fix by defining user variable

   Inside the method, assign user = User.first or similar before calling UserMailer.alert_email(user).

3. Final Answer:

   Define the variable user inside the method before calling UserMailer -> Option D

4. Quick Check:

   Undefined variable error = define variable first [OK]

Hint: Always define variables before use in preview methods [OK]

Common Mistakes:

• Assuming method name causes error
• Trying to call mailer without arguments
• Using instance variable outside method scope

5. You want to preview an email that requires a list of users. Which is the best way to write the preview method in UserMailerPreview?

hard

A. def newsletter_email
UserMailer.newsletter_email(User.all)
end

B. def newsletter_email(users)
UserMailer.newsletter_email(users)
end

C. def newsletter_email
users = User.limit(3)
UserMailer.newsletter_email(users)
end

D. def newsletter_email
UserMailer.newsletter_email
end

Solution

1. Step 1: Understand preview method context

   Preview methods do not accept parameters; they must define data inside the method.

2. Step 2: Evaluate options for passing user list

   def newsletter_email users = User.limit(3) UserMailer.newsletter_email(users) end defines a limited user list inside the method and passes it correctly. def newsletter_email(users) UserMailer.newsletter_email(users) end incorrectly defines a parameter. def newsletter_email UserMailer.newsletter_email(User.all) end passes all users which may be too large. def newsletter_email UserMailer.newsletter_email end passes no argument, likely causing error.

3. Final Answer:

   def newsletter_email users = User.limit(3) UserMailer.newsletter_email(users) end -> Option C

4. Quick Check:

   Define data inside preview method, no parameters [OK]

Hint: Preview methods must define data inside, no parameters [OK]

Common Mistakes:

• Adding parameters to preview methods
• Passing no arguments when required
• Using too large datasets in previews