Email previews in Ruby on Rails - Mini Project: Build & Apply

Email previews in Rails

📖 Scenario: You are building a Rails application that sends welcome emails to new users. To check how these emails look before sending them, you want to create email previews.

🎯 Goal: Create an email preview class for the UserMailer that shows a sample welcome email for a user named Jane Doe with the email [e-mail].

📋 What You'll Learn

Create a sample User object with name Jane Doe and email [e-mail]

Create a preview class UserMailerPreview inside test/mailers/previews

Add a method welcome_email in the preview class that calls UserMailer#welcome_email with the sample user

Ensure the preview class inherits from ActionMailer::Preview

💡 Why This Matters

🌍 Real World

Email previews help developers and designers see exactly how emails will look before sending them to real users. This avoids mistakes and improves email quality.

💼 Career

Knowing how to create and use email previews is important for Rails developers working on applications that send emails, ensuring better testing and user experience.

1

Create a sample user object

Create a variable called user that is a new User instance with name set to "Jane Doe" and email set to "[e-mail]".

Ruby on Rails

# Create a sample user object
# Your code here

Hint

Use User.new(name: "Jane Doe", email: "[e-mail]") to create the user.

2

Create the preview class

Create a class called UserMailerPreview inside the test/mailers/previews folder that inherits from ActionMailer::Preview.

Ruby on Rails

user = User.new(name: "Jane Doe", email: "[e-mail]")

# Create UserMailerPreview class inheriting from ActionMailer::Preview
# Your code here

Hint

Define UserMailerPreview as a class that inherits from ActionMailer::Preview.

3

Add the welcome_email method

Inside the UserMailerPreview class, add a method called welcome_email that returns UserMailer.welcome_email(user) using the user variable.

Ruby on Rails

user = User.new(name: "Jane Doe", email: "[e-mail]")

class UserMailerPreview < ActionMailer::Preview
  # Define welcome_email method
  # Your code here
end

Hint

Define welcome_email method that calls UserMailer.welcome_email(user).

4

Complete the preview setup

Ensure the UserMailerPreview class and the user variable are correctly defined in the same file so Rails can use this preview to show the welcome email.

Ruby on Rails

user = User.new(name: "Jane Doe", email: "[e-mail]")

class UserMailerPreview < ActionMailer::Preview
  def welcome_email
    UserMailer.welcome_email(user)
  end
end

# Confirm the preview class and user variable are set up correctly
# Your code here

Hint

Make sure the preview class and user variable are in the same file and properly defined.

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