Top Ruby on Rails Interview Questions

# app/views/layouts/application.html.erb
<%= yield %>
# app/views/layouts/admin.html.erb
<h1>Admin Panel</h1>
<%= yield %>
In the controller:
class Admin::DashboardController < ApplicationController
  layout 'admin'
end

# Instead of repeating the same validation in multiple models
class User < ApplicationRecord
  validates :email, presence: true
end
class Admin < ApplicationRecord
  validates :email, presence: true
end
# Use a module (DRY)
module EmailValidatable
  extend ActiveSupport::Concern
  included do
    validates :email, presence: true
  end
end
class User < ApplicationRecord
  include EmailValidatable
end
class Admin < ApplicationRecord
  include EmailValidatable
end

user = User.find(1)
user.delete   # Deletes from DB without callbacks
user.destroy  # Deletes from DB and triggers callbacks

# This is a single-line comment
puts "Hello World"

=begin
This is a multi-line comment
spanning multiple lines
=end
puts "Hello"

Feature	Single Quotes (‘)	Double Quotes (“)
Interpolation	Not allowed (#{} ignored)	Allowed (#{} evaluates expression)
Escape sequences	Only \ and ‘ supported	Supports all, e.g., n, t, \
Performance	Slightly faster	Slightly slower due to interpolation parsing

Example:

name = "Ayaan"
puts 'Hello #{name}'   # Output: Hello #{name}
puts "Hello #{name}"   # Output: Hello Ayaan

Double quotes are preferred when you need interpolation or special characters; otherwise, single quotes are simpler.

33. What is the purpose of the Rails server command?

The rails server (or rails s) command runs a Rails application locally. It will run a web server (like Puma, WEBrick, etc.) configured to listen for HTTP requests, allowing the developer to preview and test the application in a web browser.

Example:

rails server
# By default, runs on http://localhost:3000

The rails server command is mainly for development purposes to test functionality, debug the application, or preview the application without having to deploy it.

34. Explain the concept of RESTful routes in Rails.

RESTful routes in Rails refer to a Rails convention for mapping HTTP verbs to controller actions according to RESTful principles. RESTful routes also standardize URL patterns and make applications predictable.

Key points:

• GET /articles → index action
• GET /articles/:id → show action
• POST /articles → create action
• PATCH/PUT /articles/:id → update action
• DELETE /articles/:id → destroy action

RESTful routes help simplify routing, improve maintainability, and make APIs more intuitive.

35. What is the purpose of the config/routes.rb file?

The config/routes.rb file contains all the routes for a Rails application and maps URLs to controller actions.

Example:

Rails.application.routes.draw do
  resources :articles
end

In this case, resources :articles create RESTful routes (index, show, new, create, etc.). Routes are how Rails makes sure the user’s requests endup in the right controller action, as well as organizing user navigation within the application.

36. What is a partial in Rails, and why would you use it?

A partial is a reusable view template in Rails to avoid repeated code in views and improve maintainability.

• Naming: Begins with an underscore (_form.html.erb)
• Usage: Rendered using render in views

<%= render 'form' %>

Benefits:

• Promotes DRY code
• Simplifies complex views
• Makes templates modular and easier to maintain

Partials are especially useful for forms, headers, footers, or repeating UI components.

37. What is the role of a controller in a Rails application?

In a Rails application, a controller is a mediator between the model (data) and the view (UI). When a request comes into your application as an HTTP request, a controller gets that request, retrieves or manipulates some data using a model, and renders a view or redirect to some other action.

Example:

class ArticlesController < ApplicationController
  def index
    @articles = Article.all
  end
end

In the example above, the index action retrieves all of the articles and returns that variable to the view. The controller is the engine of the MVC architecture, in that a controller will separate logic into separate files.

38. What is the purpose of the application.rb file?

The config/application.rb file contains the basic configuration for a Rails application, including the definition of the Rails framework, middleware application to be run for all environments (development, test, production), global application configuration, and more.

Key roles:

• Load the Rails framework and all gems
• Configure default application settings including (for example) time zone, i18n, and generators
• Serve as the starting point for application configuration for environment-based files.

It is essentially the backbone of the Rails application configuration.

39. What is the difference between link_to and button_to in Rails?

Both link_to and button_to generate clickable elements, but they are used differently:

<%= link_to 'Show', article_path(@article) %><%= button_to 'Delete', article_path(@article), method: :delete %>

button_to is preferred for actions that change data, while link_to is ideal for navigation.

Intermediate Ruby on Rails Interview Questions

The intermediate interview questions shift to practical and framework-related topics like callbacks, filters, helpers, associations, authentication, and processing using background jobs. These questions assess a developer’s ability surrounding Rails concepts in applications while writing maintainable code.

40. How do you start a Rails server?

To start a Rails server, you can use either the rails server or rails s command. By default, it uses Puma as the server and listens on http://localhost:3000 .

Command:

rails server
# or
rails s

Optional parameters:

• -p 4000 → run on port 4000
• -e production → run in production environment

Since the server has been started, the Developer can test the application locally, verify routes, and debug features, if any, in a browser.

41. What are strong parameters? Explain in brief.

Strong parameters are a security feature of Rails. They prevent mass assignment vulnerabilities. They ensure only “permitted” attributes coming from forms are allowed to be passed to the model and protect sensitive fields against unintended updates.

Example:

class UsersController < ApplicationController
  def user_params
    params.require(:user).permit(:name, :email)
  end
end

In the above example, only the name and email are permitted. All other fields, if submitted, will be ignored, enhancing the security of the application.

42. Does Ruby support Single Inheritance/Multiple Inheritance or Both?

Ruby has single inheritance. A class can inherit from only one parent class. Ruby, however, achieves multiple inheritance behaviors through mixins (Modules). Modules can be mixed into multiple classes.

Example:

class Vehicle; end
class Car < Vehicle; end  # Single inheritance
module Electric; end
class Tesla < Car
  include Electric       # Mixin for multiple inheritance behavior
end

This allows code to be reused without having true multiple inheritance.

43. What are the limits of Ruby on Rails?

Rails is powerful and has limitations:

• Performance: Not as fast for CPU-heavy applications as with lower-level frameworks.
• Scalability: Larger applications that require scalability may need special design considerations.
• Flexibility: Conventions may prevent customization in some areas.
• Runtime errors: Dynamic typing may hide issues until runtime
• Memory usage: Rails apps can consume significant memory

Despite these, Rails excels in rapid development and developer productivity.

44. What is the difference between observers and callbacks in Ruby on Rails?

Observers and callbacks both respond to model events, but they differ in scope and usage:

Callbacks are inline and tightly coupled, whereas observers are decoupled and better for maintainability.

45. Explain the difference between ActiveSupport’s “HashWithIndifferentAccess” and Ruby’s “Hash”.

Ruby’s standard Hash recognizes two types of keys: symbols and strings. For instance, hash[:key] and hash[“key”] are two separate keys. HashWithIndifferentAccess allows you to use either to access its values, which is very helpful for Rails developers when working with parameters.

Example:

# Standard Hash
hash = { "name" => "Ayaan" }
hash[:name]      # => nil
hash["name"]     # => "Ayaan"
# HashWithIndifferentAccess
hash = ActiveSupport::HashWithIndifferentAccess.new(name: "Ayaan")

hash[:name]      # => "Ayaan"
hash["name"]     # => "Ayaan"

Use Case: Less code when handling params in controllers, reducing the chances of bugs related to key types.

46. What is the difference between string and text in Rails?

In Rails ActiveRecord, both string and text are used for storing textual data, but they differ in length and database handling:

Tip: Use string for indexed columns and text for long, unindexed content.

47. Explain the difference between dynamic and static scaffolding.

Scaffolding in Rails automates CRUD functionality. There are two types:

Tip: Dynamic scaffolding is mostly for learning and prototyping, while static scaffolding is used in real applications.

48. What are Filters?

Filters in Rails are methods that run before, after, or around controller actions. They are mainly used for authentication, authorization, logging, or modifying parameters.

Types of Filters:

• before_action – runs before an action
• after_action – runs after an action
• around_action – runs both before and after an action

Example:

class PostsController < ApplicationControlle
  before_action :authenticate_user!
  after_action :log_action
  def index
    @posts = Post.all
  end
  private
  def log_action
    Rails.logger.info "Action executed"
  end
end

Use Case: Filters improve code reusability and keep controllers clean and DRY.

49. What are Helpers and, how do you use Helpers in Ruby on Rails?

Helpers in Rails are modules that store methods for use in views, making view templates cleaner and more maintainable. Instead of repeating logic in multiple views, you place reusable methods in a helper module.

Example:

# app/helpers/application_helper.rb
module ApplicationHelper
  def formatted_date(date)
    date.strftime("%B %d, %Y")
  end
end

# In a view
<%= formatted_date(@post.created_at) %>

Use Case: Helpers are commonly used for:

• Formatting dates, numbers, or strings
• Generating HTML tags
• Complex display logic that shouldn’t reside in views

50. What do you mean by Render and Redirect_to?

render and redirect_to are used in controllers to control the response:

Example:

def creat
 @post = Post.new(post_params)
  if @post.save
    redirect_to @post, notice: "Post created successfully"
  else
    render :new
  end
end

Tip: Use render for showing views with existing data and redirect_to after actions that change state.

51. What is Active Job?

Active Job is a framework in Rails for declaring background jobs that can run asynchronously. It provides a standard interface and supports multiple backends like Sidekiq, Resque, Delayed Job.

Example:

# app/jobs/welcome_email_job.rb
class WelcomeEmailJob < ApplicationJob
  queue_as :default
  def perform(user)
    UserMailer.welcome_email(user).deliver_now
  end
end
# To enqueue
WelcomeEmailJob.perform_later(@user)

Use Case:

• Sending emails asynchronously
• Processing long-running tasks like CSV imports
• Scheduled tasks (with queuing backends)

Tip: Active Job decouples your code from specific queuing systems, making your app more flexible and maintainable.

52. What is the difference between After_save and After_commit?

Both after_save and after_commit are ActiveRecord callbacks, but they run at different stages of the lifecycle.

Example:

class Post < ApplicationRecord
  after_save :update_cache
  after_commit :notify_followers
  private
  def update_cache
    Rails.cache.write("post_#{id}", self)
  end
  def notify_followers
    FollowersNotifierJob.perform_later(self.id)
  end
end

Tip: Use after_commit when the operation should only occur if the database changes are successfully persisted, preventing issues from failed transactions.

53. What is an Asset Pipeline in Rails?

The Asset Pipeline in Rails is a framework that manages and serves static assets like JavaScript, CSS, and images. It preprocesses, compresses, and fingerprints assets for faster loading and easier maintenance.

Key Features:

• Concatenation: Combines multiple files into one to reduce HTTP requests
• Minification: Removes unnecessary whitespace and comments
• Fingerprints: Adds unique hashes to filenames for cache busting

Example:

# app/assets/javascripts/application.js
//= require jquery
//= require rails-ujs
//= require_tree 

Use Case:

• Reduces page load time
• Simplifies asset organization
• Supports preprocessing (e.g., SCSS, CoffeeScript)

54. What is a Callback in Ruby on Rails?

Callbacks are methods triggered at specific points in an ActiveRecord object’s lifecycle, such as creating, updating, or destroying a record. They allow you to inject logic before or after database operations.

Types of Callbacks:

• Before callbacks: before_validation, before_save
• After callbacks: after_save, after_create
• Around callbacks: Wrap actions (around_save)

Example:

class User < ApplicationRecord
  before_save :normalize_nam
  private
  def normalize_name

    self.name = name.downcase.titleize

  end

end

Use Case:

• Ensuring data consistency
• Triggering notifications or background jobs
• Automatically updating related records

55. Explain the types of Callbacks in Ruby on Rails.

Rails provides several callback types, each executed at specific stages of an object’s lifecycle:

Tip: Use callbacks judiciously. Overusing them can make debugging difficult, so keep business logic in service objects when needed.

56. What do you mean by Polymorphic Association in Rails?

Polymorphic associations allow a model to belong to more than one other model on a single association. This is useful when multiple models share the same relationship type.

Example:

# Comment can belong to Post or Photo

class Comment < ApplicationRecord

  belongs_to :commentable, polymorphic: true

end

class Post < ApplicationRecord

  has_many :comments, as: :commentable

end

class Photo < ApplicationRecord

  has_many :comments, as: :commentable

end

# Usage

post = Post.create(title: "Rails Polymorphism")

photo = Photo.create(title: "Vacation Photo")

post.comments.create(content: "Great post!")

photo.comments.create(content: "Nice picture!")

Use Case:

• Comments, tags, or likes on multiple models
• Reduces duplication by reusing the same association

Tip: Always include a type column (commentable_type) and id column (commentable_id) in the polymorphic table.

57. What is the difference between has_many :through and has_and_belongs_to_many and which one is better?

Both are used to model many-to-many relationships, but they differ in flexibility:

Best Practice:

• Use has_many :through if you need extra attributes or callbacks on the join table.
• HABTM is suitable for simple join tables without additional logic.

58. Do you know about ActiveStorage in Ruby on Rails and how can you use this?

ActiveStorage is Rails’ built-in file attachment framework for managing uploads like images, videos, and documents. It supports cloud storage services (Amazon S3, Google Cloud, Azure) as well as local storage.

Basic Usage:

class User < ApplicationRecord

  has_one_attached :avatar

end

# Attach a file

user.avatar.attach(io: File.open('/path/to/avatar.jpg'), filename: 'avatar.jpg')

# Access the file

user.avatar.url

Use Cases:

• Profile pictures, document uploads, and media attachments
• Integrates with ActiveJob for background processing
• Handles variants (resizing images) easily

Tip: ActiveStorage replaces older gems like Paperclip for simpler file management.

59. What are Accessor Methods in Ruby?

Accessor methods are getters and setters that allow controlled access to an object’s instance variables. Ruby provides three built-in macros for creating them:

Example:

class User

  attr_accessor :name

end

user = User.new

user.name = "Ayaan"   # setter

puts user.name        # getter

Use Case:

• Provides encapsulation
• Avoids manually writing getter and setter methods

60. What is the difference between super and super() call?

Both super and super() are used to call the parent class method, but they differ in argument passing:

Example:

class Parent

  def greet(name)

    puts "Hello, #{name}"

  end

end

class Child < Parent

  def greet(name)

    super      # passes `name` automatically

    puts "Welcome!"

  end

end

Child.new.greet("Ayaan")

Tip: Use super() when you don’t want to pass arguments, ensuring more explicit control over method behavior.

61. What are the different types of Association in Rails?

Rails provides several association types to define relationships between models:

Use Case:

• Proper association helps in query optimization, nested forms, and ActiveRecord methods like includes and joins.

62. Explain with the help of an example Skip Callback in Rails.

Callbacks run before/after certain actions in Rails models. Sometimes, you may skip a callback for specific cases.

Example:

class User < ApplicationRecord

  before_save :normalize_name

  def normalize_name

    self.name = name.downcase

  end

end

# Skip callback

user = User.new(name: "Ayaan")

user.save!(validate: false) # Skips callbacks using save!(validate: false)

Use Case:

• Useful when importing bulk data, performing manual updates, or bypassing expensive operations.

63. What do you mean by Concerns in Rails?

Concerns are modules used to share reusable code across models or controllers. They follow DRY principles and help organize logic efficiently.

Example:

# app/models/concerns/auditable.rb

module Auditable

  extend ActiveSupport::Concern

  included do

    before_save :track_changes

  end

  def track_changes

    puts "Changes tracked!"

  end

end

class User < ApplicationRecord

  include Auditable

end

Use Case:

• Extract common logic like auditing, notifications, or authentication
• Keeps models/controllers clean and maintainable

64. Explain what Destroy does in Ruby on Rails.

destroy is used to delete a record from the database along with any associated dependent objects if specified.

Example:

class User < ApplicationRecord

  has_many :posts, dependent: :destroy

end

user = User.find(1)

user.destroy  # deletes user and all associated posts

Difference from delete:

65. How do you define associations between models in Rails (e.g., has_many, belongs_to)?

Associations define how models are related. Rails provides macros like has_many, belongs_to, has_one, and has_many :through to set up these relationships.

Example:

class Author < ApplicationRecord

  has_many :books

end

class Book < ApplicationRecord

  belongs_to :author

end

Use Case:

• Enables ActiveRecord methods like author.books
• Helps join queries, nested forms, and data integrity

66. What is the purpose of the before_action callback in Rails?

before_action runs specified methods before controller actions. It is commonly used for authentication, authorization, or setting variables.

Example:

class ArticlesController < ApplicationController

  before_action :find_article, only: [:show, :edit, :update, :destroy]

  def show

  end

  private

  def find_article

    @article = Article.find(params[:id])

  end

end

Use Case:

• Avoids repeating code in multiple actions
• Ensures security and consistency across controller actions

67. How do you implement user authentication using Devise in Rails?

Devise is a popular authentication gem that provides ready-to-use modules like registration, login, password recovery, and more.

Steps:

1. Add to Gemfile:
   gem ‘devise’
   
2. Install Devise:
   rails generate devise:install
3. Generate User model:
   rails generate devise User
   rails db:migrate
4. Use Devise helpers in controllers/views:
   before_action :authenticate_user!

Use Case:

• Quick and secure user authentication
• Handles sessions, password encryption, and email confirmations

68. How can you implement role-based authorization in Rails?

Role-based authorization controls what users can access based on their roles (admin, editor, user).

Example using Pundit gem:

1. Add to Gemfile:
   gem ‘pundit’
2. Generate policy:
   rails generate pundit:install
   rails generate pundit:policy Article
3. Define permissions:
   class ArticlePolicy < ApplicationPolicy
   def update?
   user.admin? || record.user_id == user.id
   end
   end
4. Apply in controller:
   def update
   @article = Article.find(params[:id])
   authorize @article
   end

Use Case:

• Secures sensitive actions
• Implements fine-grained access control

69. What is a scope in Rails, and how do you define it?

Scopes allow you to encapsulate commonly-used queries in a model for cleaner, reusable code. They help keep controllers slim and improve readability.

Example:

class Article < ApplicationRecord
  scope :published, -> { where(published: true) }
  scope :recent, -> { order(created_at: :desc) }
end

Usage:

Article.published.recent

Use Case:

• Reusable query logic
• Can chain multiple scopes together for complex queries

70. How do you handle background jobs in Rails (e.g., using Sidekiq or ActiveJob)?

Background jobs allow long-running tasks to run asynchronously, freeing up web requests to respond faster. Rails provides ActiveJob, which works with adapters like Sidekiq, Resque, or Delayed Job.

Example using Sidekiq with ActiveJob:

class SendEmailJob < ApplicationJob

  queue_as :default

  def perform(user)

    UserMailer.welcome_email(user).deliver_now

  end

end

Triggering the job:

SendEmailJob.perform_later(@user)

Use Case:

• Sending emails, generating reports, image processing
• Improves performance and scalability

71. What is caching in Rails, and how do you implement it?

Caching stores frequently accessed data to reduce database queries and improve performance. Rails supports multiple types: fragment, page, action, and low-level caching.

Example (Fragment Caching):

<% cache @article do %>

  <%= render @article %>

<% end %>

Use Case:

• Speeds up response time for high-traffic pages
• Reduces load on the database
• Can be implemented with Redis or Memcached

72. How do you handle file uploads in Rails (e.g., using ActiveStorage or CarrierWave)?

Rails provides ActiveStorage to attach files to models. CarrierWave is an alternative gem for advanced customization.

Example using ActiveStorage:

class User < ApplicationRecord

  has_one_attached :avatar

end

Uploading via form:

<%= form.file_field :avatar %>

Use Case:

• Handles images, PDFs, videos
• Supports cloud storage (AWS S3, Google Cloud)
• Automatically manages file attachment, validation, and retrieval

73. Explain the use of respond_to in controllers.

The respond_to method in Rails controllers allows a single action to respond to different formats such as HTML, JSON, XML, or JS. It is essential for building API-friendly applications and providing format-specific responses.

Example:

def show

  @article = Article.find(params[:id])

  respond_to do |format|

    format.html

    format.json { render json: @article }

  end

end

Use Case:

• Responding with HTML for web users
• Responding with JSON for API clients
• Ensures controllers are flexible and reusable

74. How do you handle form submissions with nested attributes in Rails?

Nested attributes allow you to save attributes on associated models through the parent model. This is particularly useful for forms that manage multiple models at once.

Example:

class Project < ApplicationRecord

  has_many :tasks

  accepts_nested_attributes_for :tasks

end

Form Example:

<%= form_with(model: @project) do |f| %>

  <%= f.text_field :name %>

  <%= f.fields_for :tasks do |t| %>

    <%= t.text_field :title %>

  <% end %>

<% end %>

Use Case:

• Creating a project along with multiple tasks in one form submission
• Simplifies handling complex associations

75. How do you implement API versioning in a Rails application?

API versioning allows you to maintain multiple API versions without breaking existing clients. Rails supports versioning via namespaced routes or headers.

Example (Namespace Versioning):

namespace :api do

  namespace :v1 do

    resources :articles

  end

  namespace :v2 do

    resources :articles

  end

end

Use Case:

• Supports backward compatibility
• Allows iterative improvements of APIs
• Critical for public APIs consumed by multiple clients

76. What is the purpose of before_action callback in Rails?

before_action is a Rails controller callback that runs specified methods before an action executes. It is commonly used for authentication, authorization, or setting up variables.

Example:

class ArticlesController < ApplicationController

  before_action :set_article, only: [:show, :edit, :update, :destroy]

  private

  def set_article

    @article = Article.find(params[:id])

  end

end

Use Case:

• Reduces code repetition
• Ensures actions are executed in a controlled and predictable manner
• Improves maintainability and readability

77. How do you implement user authentication using Devise in Rails?

Devise is a popular gem for authentication in Rails. It provides ready-made modules for handling sign-up, login, password recovery, and more. To implement:

1. Add Devise to Gemfile:
   gem ‘devise’
2. Run:
   bundle install
   rails generate devise:install
   rails generate devise User
   rails db:migrate
3. Add authentication filters in controllers:
   before_action :authenticate_user!

Devise simplifies secure authentication, handling hashing, sessions, and validations.

78. How can you implement role-based authorization in Rails?

Role-based authorization restricts access to actions based on user roles. Commonly implemented using gems like Pundit or CanCanCan, or manually with conditional logic in controllers.

Example (Simple Manual Check):

def admin_only

  redirect_to root_path unless current_user.admin?

end

before_action :admin_only, only: [:destroy]

This ensures secure control over sensitive actions in an application.

79. What is a scope in Rails, and how do you define it?

A scope is a custom query method defined in a model for reuse and readability. It simplifies querying and keeps code DRY.

Example:

class Article < ApplicationRecord

  scope :published, -> { where(published: true) }

end

You can call it like:

Article.published

Scopes make complex queries concise and chainable.

Advanced Ruby on Rails Interview Questions

Advanced interview questions focus on performance, scaling, and architecture principles in Rails applications. These questions are intended to test a developer’s expertise that relates to building and maintaining a complex Rails application, fit for production use.

80. How do you handle background jobs in Rails (e.g., using Sidekiq or ActiveJob)?

Background jobs allow long-running tasks to run asynchronously, keeping requests fast. Rails provides ActiveJob as a wrapper for adapters like Sidekiq, Resque, or DelayedJob.

Example (ActiveJob with Sidekiq):

class EmailJob < ApplicationJob

  queue_as :default

  def perform(user_id)

    UserMailer.welcome_email(User.find(user_id)).deliver_now

  end

end

Trigger the job:
EmailJob.perform_later(current_user.id)

This approach decouples heavy tasks from user requests, improving performance.

81. How do you optimize the performance of a Ruby on Rails application?

Performance optimization in Rails involves multiple layers:

• Database optimization: Use indexes, avoid N+1 queries, and optimize ActiveRecord queries.
• Caching: Implement fragment, page, or low-level caching to reduce redundant computations.
• Asset optimization: Compress CSS/JS and use the asset pipeline effectively.
• Background processing: Offload heavy tasks to background jobs using Sidekiq or ActiveJob.
• Query batching: Use includes, joins, or pluck to fetch only necessary data.
• Server and environment tuning: Use multithreaded servers like Puma, optimize memory usage, and precompile assets.
  A combination of database, code, and infrastructure improvements ensures scalable performance.

82. Can you discuss your experience with Rails API mode for building APIs?

Rails API mode allows building lightweight, backend-only applications without views and frontend assets, ideal for JSON APIs.

• Use rails new myapp –api to generate an API-only app.
• Middleware is minimized for faster response times.
• Combine with ActiveModelSerializers or Fast JSON API for structured JSON output.
• Easily integrates with authentication tools like JWT or Devise Token Auth.
• Supports versioning and namespaced controllers for maintaining multiple API versions.

Rails API mode is efficient, scalable, and suitable for mobile apps or single-page applications.

83. How do you implement background processing in a Rails application?

Background processing lets Rails offload long-running tasks like sending emails, processing files, or generating reports.

• Rails provides ActiveJob, a framework to wrap background jobs.
• Sidekiq is a popular adapter, using Redis to manage job queues.
• Jobs are enqueued asynchronously:

class ReportJob < ApplicationJob

  queue_as :default

  def perform(report_id)

    Report.generate(report_id)

  end

end

ReportJob.perform_later(@report.id)

• Benefits: Improves response time, reduces user wait, and scales tasks efficiently.

Proper monitoring of queues ensures job reliability and performance.

84. What strategies do you use for database scaling and optimization in Rails?

Scaling Rails databases involves horizontal and vertical strategies:

• Indexing: Speed up queries on frequently accessed columns.
• Query optimization: Avoid N+1 queries with includes or joins.
• Database sharding: Split large datasets across multiple databases.
• Read replicas: Use replicas for read-heavy operations, separating writes from reads.
• Connection pooling: Optimize ActiveRecord database connections for high concurrency.
• Partitioning: Divide tables into partitions for large datasets.
• Caching queries: Use Redis or Memcached to cache frequent query results.

Combining query optimization, caching, and scaling infrastructure helps Rails apps handle high traffic efficiently.

85. Can you explain how to use WebSockets in Rails?

WebSockets allow real-time, bidirectional communication between client and server. Rails supports this via Action Cable:

• Integrates seamlessly with Rails applications.
• Uses channels to broadcast messages to subscribed clients.
• Example setup:

# app/channels/chat_channel.rb

class ChatChannel < ApplicationCable::Channel

  def subscribed

    stream_from "chat_#{params[:room]}"

  end

  def speak(data)

    ActionCable.server.broadcast("chat_#{params[:room]}", message: data['message'])

  end

end

• On the frontend, clients can subscribe to channels using JavaScript.
• Common use cases: live notifications, chat applications, and dashboards.

Rails handles connections, subscriptions, and broadcasting, making real-time features easier to implement.

86. How have you integrated microservices with a Rails application?

Integrating microservices involves breaking a monolithic Rails app into smaller services:

• Each service handles a specific domain and communicates via HTTP/REST, GraphQL, or message queues.
• Rails apps can expose APIs using Rails API mode or consume other services using HTTP clients like Faraday or HTTParty.
• Services may share Redis, Kafka, or RabbitMQ for asynchronous messaging.
• Benefits: scalability, independent deployments, and fault isolation.

A proper service boundary definition ensures each microservice remains loosely coupled and maintainable.

87. What are the best practices for securing a Ruby on Rails application?

Security in Rails is crucial to protect user data and application integrity:

• Authentication & Authorization: Use Devise, Pundit, or CanCanCan.
• CSRF protection: Rails has built-in mechanisms to prevent Cross-Site Request Forgery.
• Input validation & sanitization: Prevent SQL injection and XSS attacks.
• Secure headers: Implement Content Security Policy (CSP) and HTTP-only cookies.
• Encrypt sensitive data: Use Rails’ ActiveSupport::MessageEncryptor or database encryption.
• Regular updates: Keep Rails and gems up-to-date to patch vulnerabilities.

Combining Rails defaults with additional security layers ensures a robust, secure application.

88. Can you describe your approach to Test-Driven Development (TDD) in Rails?

TDD ensures high-quality, maintainable Rails applications:

• Write a failing test first using RSpec or Minitest.
• Implement just enough code to pass the test.
• Refactor the code for readability and performance.
• Types of tests:

• Unit tests: Test individual models or methods.
• Integration tests: Test interactions between multiple components.
• System tests: End-to-end testing of user flows.

• Example with RSpec:

RSpec.describe User, type: :model do

  it "is valid with valid attributes" do

    user = User.new(name: "Ayaan", email: "[email protected]")

    expect(user).to be_valid

  end

end

TDD ensures early bug detection, better design, and confidence in changes.

89. How do you manage and optimize ActiveRecord queries for large datasets?

Managing large datasets efficiently is critical for performance:

• Use select to fetch only the required columns.
• Employ includes eager_load, or preload to avoid N+1 queries.
• Use find_each or find_in_batches for processing large collections without loading everything into memory.
• Apply database-level optimizations like indexes and query caching.
• Example:

# Using find_each for a large dataset

User.find_each(batch_size: 1000) do |user|

  process(user)

end

Optimizing queries reduces memory consumption and response time significantly.

90. What techniques do you use for memory management in a Rails application?

Memory management ensures Rails applications remain responsive under load:

• Avoid loading unnecessary objects; prefer pluck over map when retrieving only specific fields.
• Use find_each for batch processing.
• Monitor memory usage with tools like New Relic, Skylight, or Bullet.
• Properly close file handles, DB connections, and cache objects.
• Consider garbage collection tuning for large applications.
• Optimize ActiveRecord objects to prevent memory leaks.

Effective memory management leads to faster performance and reduced server crashes.

91. How do you implement single sign-on (SSO) in a Ruby on Rails application?

Single Sign-On allows users to authenticate once and access multiple systems:

• Use OmniAuth or Devise with OmniAuth for integrating third-party identity providers.
• Common SSO providers: OAuth2, SAML, OpenID Connect.
• Steps:

1. Configure OmniAuth with provider credentials.
2. Redirect users to the provider for authentication.
3. Receive and validate the callback with user info.
4. Create or update user in Rails database.

• Example (Devise + OmniAuth):

# config/initializers/devise.rb

config.omniauth :google_oauth2, “GOOGLE_CLIENT_ID”, “GOOGLE_CLIENT_SECRET”

SSO simplifies user experience and centralizes authentication.

92. Can you discuss your experience with deploying Rails applications using Docker?

Docker simplifies consistent deployment and environment management:

• Create a Dockerfile with Ruby, dependencies, and Rails app setup.
• Use docker-compose for multi-service applications (e.g., Rails + PostgreSQL + Redis).
• Benefits:
  • Consistent environments across development, staging, and production.
  • Easy scaling and integration with CI/CD pipelines.
  • Example Dockerfile snippet:

FROM ruby:3.2

WORKDIR /app

COPY Gemfile* ./

RUN bundle install

COPY . .

CMD ["rails", "server", "-b", "0.0.0.0"]

Docker ensures portability, reproducibility, and simplified infrastructure management.

93. What is your approach to versioning a Rails API?

Versioning ensures that changes in an API do not break existing clients:

• Common approaches:
  • URL versioning: /api/v1/users
  • Header versioning: Using Accept headers like application/vnd.myapp.v1+json
  • Namespace controllers: Place versioned controllers in folders, e.g., app/controllers/api/v1/users_controller.rb
• Benefits:
  • Allows incremental improvements without affecting existing users.
  • Simplifies backward compatibility management.

• Example:

# config/routes.rb

namespace :api do

  namespace :v1 do

    resources :users

  end

end

94. How do you handle multi-tenancy in a Rails application?

Multi-tenancy allows a single application to serve multiple independent clients:

• Approaches:
  • Separate databases per tenant – isolates data fully.
  • Shared database with schema per tenant – maintains separate tables or schemas.
  • Shared database, shared schema – use a tenant_id column for scoping.
  • Gems like Apartment help manage multi-tenancy.
• Benefits:
  • Efficient use of resources.
  • Data isolation and security.
• Example:

# Using Apartment gem

Apartment::Tenant.switch!("tenant_name") do

  User.create(name: "Tenant User")

end

95. Can you explain the process of upgrading a Rails application to a newer version?

Upgrading Rails requires careful planning:

1. Review changelogs for breaking changes and deprecations.
2. Update Ruby version if required.
3. Upgrade gems incrementally.
4. Run test suite to detect issues.
5. Address deprecated methods and syntax.
6. Deploy in staging before production.

• Example: Rails 6 → Rails 7 upgrade may involve updating Webpacker to jsbundling-rails.
• Key point: Always backup the database and code before upgrading.

96. What are the challenges you have faced in Rails application scaling, and how did you overcome them?

Scaling a Rails app involves both performance and infrastructure challenges:

• Challenges:

• • Slow database queries: solved with indexes, query optimization, caching.
  • High memory usage: optimized with batch processing, GC tuning, background jobs.
  • Increased traffic: handled using load balancers and horizontal scaling.
  • Asset management: implemented CDN and asset precompilation.
• Strategies:
  • Caching layers: page, fragment, and query caching.
  • Background processing: Sidekiq or ActiveJob.
  • Horizontal scaling: multiple app servers behind a load balancer.
  • Scaling requires monitoring, profiling, and continuous optimization.

97. How do you monitor and ensure the health of a Rails application in production?

Monitoring is crucial to maintain uptime and performance:

• Use application performance monitoring (APM) tools like New Relic, Datadog, or Scout to track response times and errors.
• Implement logging with tools like Lograge and centralized log management via ELK Stack or Papertrail.
• Set up health checks and alerts for key endpoints or background jobs.
• Monitor database metrics such as slow queries, connection pool usage, and cache hit rates.
• Benefits: Early detection of performance bottlenecks, proactive issue resolution, and improved reliability.

98. Can you discuss the implementation of custom authentication systems in Rails?

While Devise is widely used, custom authentication provides full control:

• Steps:

1. 1. Create a User model with email and encrypted_password.
   2. Use bcrypt gem for password hashing.
   3. Implement sessions controller for login/logout.
   4. Add before_action filters to protect sensitive routes.

• Example:

# app/models/user.rb

has_secure_password

# app/controllers/sessions_controller.rb

def create

  user = User.find_by(email: params[:email])

  if user&.authenticate(params[:password])

    session[:user_id] = user.id

    redirect_to dashboard_path

  else

    render :new, alert: "Invalid credentials"

  end

end

• Benefits: Tailored to application needs, integrates with role-based access, and supports custom security policies.

99. How do you manage and optimize ActiveRecord queries for large datasets?

Optimizing ActiveRecord is key for performance with big data:

• Use select to fetch only necessary columns.
• Avoid N+1 queries using includes, eager_load, or preload.
• Use find_each for batch processing instead of all.
• Index frequently queried columns.
• Example:

# Avoid N+1

posts = Post.includes(:comments).where(published: true)

posts.each do |post|

  puts post.comments.count

end

• Benefits: Reduces database load, improves response times, and scales efficiently.

100. What techniques do you use for memory management in a Rails application?

Memory management prevents bloating and crashes:

• Identify memory leaks using ObjectSpace and memory_profiler.
• Avoid loading large datasets in memory; use find_each or pagination.
• Use memoization carefully; ensure caches don’t grow unbounded.
• Monitor GC (Garbage Collection) stats to tune Ruby runtime parameters.
• Benefits: Improved application stability, reduced server cost, and smoother user experience.

101. How do you implement single sign-on (SSO) in a Ruby on Rails application?

SSO allows users to log in once and access multiple applications:

• Use protocols like OAuth2, SAML, or OpenID Connect.
• Gems such as omniauth provide integration with providers like Google, Facebook, or corporate IdPs.
• Implementation:

1. Configure omniauth strategy for your provider.
2. Handle callback routes in a controller.
3. Create or find a user based on provider UID.

# Example: Omniauth callback

def google_oauth2

  user = User.from_omniauth(request.env['omniauth.auth'])

  session[:user_id] = user.id

  redirect_to dashboard_path

end

• Benefits: Seamless user experience, reduced password fatigue, and centralized authentication.

102. Can you discuss your experience with deploying Rails applications using Docker?

Docker simplifies deployment and environment consistency:

• Create a Dockerfile specifying Ruby, Node, and other dependencies.
• Use docker-compose to manage database and other services.
• Example:

FROM ruby:3.2

WORKDIR /app

COPY Gemfile* ./

RUN bundle install

COPY . .

CMD ["rails", "server", "-b", "0.0.0.0"]

• Benefits:

• • Isolated, reproducible environment.
  • Simplifies CI/CD pipelines.
  • Easier scaling across multiple servers or containers.

103. What is your approach to versioning a Rails API?

Versioning ensures backward compatibility for API consumers:

• Common approaches:

• • URL versioning: /api/v1/users
  • Header versioning: Accept: application/vnd.app.v1+json
• Implementation:
  • Create namespaced controllers for each version:

# config/routes.rb

namespace :api do

  namespace :v1 do

    resources :users

  end

end

• Benefits: Allows safe evolution of the API without breaking existing clients.

104. How do you handle multi-tenancy in a Rails application?

Multi-tenancy allows a single application to serve multiple clients with isolated data:

• Approaches:

1. Schema-based: Separate database schema per tenant.
2. Row-based: Single database, rows tagged by tenant_id.

• Gems like Apartment simplify schema-based multi-tenancy.
• Consider scoping queries and isolating user sessions per tenant.

105. Can you explain the process of upgrading a Rails application to a newer version?

Upgrading Rails requires careful planning to avoid breaking changes:

• Steps:

1. Check gem compatibility: Ensure all gems support the new Rails version.
2. Update Rails version in Gemfile and run bundle update rails.
3. Review deprecations using rails app:update and logs.
4. Run tests and fix failures.
5. Update configuration files as required.

• Benefits: Access to new features, security patches, and performance improvements.

106. What are the challenges you have faced in Rails application scaling and how did you overcome them?

Scaling a Rails app requires addressing both database and application performance:

• Common challenges:

• • Slow database queries → use indexing, caching, and query optimization.
  • High memory usage → implement background jobs, reduce N+1 queries.
  • Heavy traffic spikes → employ load balancers and horizontal scaling.
• Tools: Redis caching, Sidekiq for background jobs, and AWS/GCP scaling options.

107. How do you monitor and ensure the health of a Rails application in production?

Monitoring ensures availability and reliability:

• Use monitoring tools like NewRelic, Datadog, or Scout.
• Check performance metrics: response time, error rate, memory usage.
• Implement logging and exception tracking with tools like Sentry or Rollbar.
• Automate alerts for downtime or performance degradation.

108. Can you discuss the implementation of custom authentication systems in Rails?

Custom authentication allows full control over login logic:

• Steps:

1. Create User model with email and password_digest.
2. Use has_secure_password to handle password hashing.

# app/models/user.rb

class User < ApplicationRecord

  has_secure_password

end

1. Implement sessions controller to manage login/logout.
2. Use before_action filters to protect private routes.

• Benefits: Tailored authentication logic, flexible security policies, and integration with custom roles and permissions.

109. How do you manage and optimize Rails assets in a large-scale application?

Asset management is crucial for performance and maintainability:

• Use the Asset Pipeline to compress and bundle JS/CSS.
• Implement lazy loading and caching for images and assets.
• Consider Webpacker or importmaps for modern JS management.
• Use CDN to deliver assets globally and reduce server load.
• Benefits: Faster page load, reduced bandwidth usage, and improved UX.

110. What are your strategies for code refactoring in a mature Rails codebase?

Refactoring ensures maintainable and readable code:

• Identify code smells: long methods, repeated logic, or deeply nested conditionals.
• Break fat controllers/models into services, concerns, or decorators.
• Write or maintain automated tests to ensure safety.
• Use Rubocop and other linters for consistent style.
• Benefits: Easier onboarding, fewer bugs, and improved performance.

111. How do you ensure data integrity and consistency in Rails applications?

Data integrity is guaranteed at the database level as well as the application level:

• Use ActiveRecord validations that enforce rules (e.g., validates :email, presence: true). 
• Implement NOT NULL, UNIQUE and foreign key constraints at the database level. 
• Use transactions to ensure either all operations succeed or have no effect (e.g. if one operation fails).

ActiveRecord::Base.transaction do

  order.save!

  inventory.update!(stock: inventory.stock - 1)

end

Benefits: Prevents the storage of invalid or inconsistent data and supports reliable business logic.

112. Can you explain the use of service objects in Ruby on Rails?

Service objects encapsulate business logic outside of controllers/models:

• Purpose:To eliminate fat models/controllers where complex operations occur.
• Implementation:

# app/services/order_processor.rb

class OrderProcessor

  def initialize(order)

    @order = order

  end

  def call

    validate_order

    charge_payment

    update_inventory

  end

  private

  def validate_order; end

  def charge_payment; end

  def update_inventory; end

end

Conclusion

Ruby on Rails is still one of the most developer-friendly frameworks for building scalable, maintainable, high-performance web applications. It’s important to have an understanding of Rails core concepts, MVC architecture, Active Record associations, and performance optimization techniques for interviews, whether they are beginner, intermediate, or expert level.

These Ruby on Rails interview questions and answers cover everything from basic syntax and conventions to advanced topics such as caching, background jobs, and API versioning, giving you both conceptual and applied understanding.

To set yourself apart in an interview, focus on writing clean, modular code, show your knowledge of Rails best practices, and explain challenges you have solved in the real world using Rails. These concepts will prepare you for interviews and help you develop as a competent Rails developer for modern web application development.

Ruby on Rails Interview Questions – FAQs