Sending emails from controllers in Ruby on Rails - Step-by-Step Execution

Concept Flow - Sending emails from controllers

User triggers action in controller

↓

Controller calls mailer method

↓

Mailer prepares email content

↓

Mailer sends email asynchronously

↓

Controller renders response to user

This flow shows how a controller action triggers a mailer to prepare and send an email, then responds to the user.

Execution Sample

Ruby on Rails

class UsersController < ApplicationController
  def welcome
    @user = User.find(params[:id])
    UserMailer.with(user: @user).welcome_email.deliver_later
    render plain: "Email sent"
  end
end

Controller action calls mailer to send a welcome email asynchronously, then responds with a confirmation.

Execution Table

Step	Action	Controller State	Mailer State	Result
1	User requests welcome action	No email sent yet	No mailer called	Waiting for action
2	Controller calls UserMailer.with(user: @user).welcome_email.deliver_later	Preparing to send email	Mailer prepares email with user data	Email queued for sending
3	Mailer sends email asynchronously	Email sending in background	Email sent to user inbox	Email delivered
4	Controller renders response	Email queued	Mailer finished	User sees 'Email sent' message

💡 Email is sent asynchronously; controller finishes response immediately after queuing email.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
@user	nil	User object assigned	User object unchanged	User object unchanged
email_status	none	queued	sent	sent

Key Moments - 2 Insights

Why does the controller finish rendering before the email is sent?

Because deliver_later queues the email to be sent asynchronously, so the controller does not wait for the email to be delivered (see execution_table step 3 and 4).

What does UserMailer.with(user: @user) do?

It sets up the mailer with the user data so the mailer can use it to build the email content (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the email actually sent?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Check the 'Result' column for when the email is delivered.

According to the variable tracker, what is the value of email_status after step 2?

A "sent"

B "queued"

C "none"

D "failed"

💡 Hint

Look at the 'email_status' row under 'After Step 2' column.

If we replace deliver_later with deliver_now, how would the controller behavior change?

A Controller waits until email is sent before rendering response

B Controller sends email asynchronously as before

C Controller skips sending email

D Controller crashes

💡 Hint

deliver_now sends email immediately, blocking controller until done.

Concept Snapshot

Sending emails from controllers in Rails:
- Controller calls mailer method with data
- Use deliver_later to send email asynchronously
- Controller renders response immediately
- Use deliver_now to send email synchronously
- Mailer builds email content using passed data

Full Transcript

In Rails, sending emails from controllers involves calling a mailer method inside a controller action. The controller triggers the mailer with user data, then calls deliver_later to queue the email for asynchronous sending. This means the controller does not wait for the email to be sent and immediately renders a response to the user. The mailer prepares the email content using the passed user data and sends the email in the background. This approach keeps the user experience fast and responsive. Alternatively, deliver_now sends the email immediately, making the controller wait until sending finishes.

Practice

1. What is the main role of a controller when sending emails in Rails?

easy

A. To call the mailer method and trigger the email sending

B. To write the email content and layout

C. To configure the SMTP settings

D. To store email templates in the database

Solution

1. Step 1: Understand controller responsibility

   Controllers handle user requests and trigger actions like sending emails by calling mailer methods.

2. Step 2: Identify mailer role

   Mailers contain email content and setup, not controllers.

3. Final Answer:

   To call the mailer method and trigger the email sending -> Option A

4. Quick Check:

   Controllers trigger mailers [OK]

Hint: Controllers trigger mailers, mailers build emails [OK]

Common Mistakes:

• Writing email content in controllers
• Configuring SMTP in controllers
• Storing templates in controllers

2. Which of the following is the correct syntax to send an email immediately from a controller using a mailer named UserMailer and a method welcome_email?

easy

A. UserMailer.welcome_email.deliver_later(params[:user])

B. UserMailer.welcome_email(params[:user]).deliver_now

C. UserMailer.deliver_now.welcome_email(params[:user])

D. UserMailer.welcome_email(params[:user]).send_now

Solution

1. Step 1: Identify mailer method call

   The mailer method is called with parameters: UserMailer.welcome_email(params[:user]).

2. Step 2: Use correct delivery method

   To send immediately, use deliver_now after the mailer method call.

3. Final Answer:

   UserMailer.welcome_email(params[:user]).deliver_now -> Option B

4. Quick Check:

   Immediate send = deliver_now after mailer call [OK]

Hint: Call mailer method then add .deliver_now for immediate send [OK]

Common Mistakes:

• Using deliver_later for immediate send
• Calling deliver_now before mailer method
• Using non-existent send_now method

3. Given this controller code snippet:

def create
  @user = User.new(user_params)
  if @user.save
    UserMailer.welcome_email(@user).deliver_later
    redirect_to root_path, notice: 'User created!'

What happens when this code runs successfully?

medium

A. The welcome email is sent immediately before redirecting

B. The redirect happens only after the email is sent

C. The welcome email is queued to be sent later, then redirect happens

D. The email is never sent because deliver_later is incorrect here

Solution

1. Step 1: Understand deliver_later behavior

   Calling deliver_later queues the email to be sent asynchronously in the background.

2. Step 2: Analyze controller flow

   The redirect happens immediately after queuing the email, not waiting for sending.

3. Final Answer:

   The welcome email is queued to be sent later, then redirect happens -> Option C

4. Quick Check:

   deliver_later queues email, redirect immediate [OK]

Hint: deliver_later queues email, does not block controller [OK]

Common Mistakes:

• Thinking deliver_later sends email immediately
• Assuming redirect waits for email sending
• Believing deliver_later is invalid syntax

4. Identify the error in this controller code snippet:

def notify
  UserMailer.notify_user.deliver_now(user)
  redirect_to dashboard_path
end

medium

A. deliver_now is not a valid method for sending emails

B. redirect_to should be called before sending email

C. notify_user method cannot be called without parentheses

D. deliver_now should be called after passing user argument to notify_user

Solution

1. Step 1: Check method call order

   The user argument must be passed to notify_user before calling deliver_now.

2. Step 2: Correct syntax

   Correct call: UserMailer.notify_user(user).deliver_now.

3. Final Answer:

   deliver_now should be called after passing user argument to notify_user -> Option D

4. Quick Check:

   Pass args before deliver_now [OK]

Hint: Pass arguments inside mailer method, then call deliver_now [OK]

Common Mistakes:

• Calling deliver_now with arguments
• Calling redirect_to before email
• Misusing parentheses in method calls

5. You want to send a confirmation email from a controller only if the user has a verified email address. Which is the best way to implement this?

hard

A. In the controller, check if user.verified? then call UserMailer.confirmation_email(user).deliver_now

B. Always call UserMailer.confirmation_email(user).deliver_now and check verification inside the mailer

C. Send the email unconditionally and add a condition in the email template

D. Call UserMailer.confirmation_email.deliver_now(user) without any condition

Solution

1. Step 1: Decide where to check condition

   Controller should decide if email should be sent based on user verification status.

2. Step 2: Call mailer only when condition is true

   Call UserMailer.confirmation_email(user).deliver_now only if user.verified? is true.

3. Final Answer:

   In the controller, check if user.verified? then call UserMailer.confirmation_email(user).deliver_now -> Option A

4. Quick Check:

   Check condition in controller before sending email [OK]

Hint: Check conditions in controller before calling mailer [OK]

Common Mistakes:

• Checking conditions inside mailer or template
• Sending emails unconditionally
• Passing arguments after deliver_now