Top 10 Ruby on Rails Developer Interview Questions & Answers in 2024

1. How does Rails implement and handle ActiveRecord callbacks, and what are some scenarios where using callbacks might be advantageous or problematic?

Rails uses ActiveRecord callbacks to execute certain code at specific points in the object's lifecycle, such as before or after saving to the database. Examples include before_save or after_commit. Advantages include maintaining data integrity and encapsulating business logic, but excessive or poorly managed callbacks can lead to performance issues and code complexity.

2. Explain the purpose and usage of ActiveRecord associations in Rails, and provide examples of when to use has_many, belongs_to, and has_and_belongs_to_many associations.

ActiveRecord associations define relationships between models in Rails. Use has_many for one-to-many relationships, belongs_to for the corresponding side of the relationship, and has_and_belongs_to_many for many-to-many relationships. For example:

class Author < ApplicationRecord
  has_many :books
end

class Book < ApplicationRecord
  belongs_to :author
end

3. Discuss the concept of Rails middleware, and provide examples of custom middleware that can be used to modify or intercept HTTP requests and responses.

Rails middleware are modules that intercept requests and responses at various points during the request lifecycle. Examples include Rack::Logger for logging, or custom middleware for handling authentication or modifying headers. Middleware can be inserted in the application stack using config.middleware.use in the application.rb file.

4. How does Rails handle CSRF protection, and what are the security considerations when implementing and customizing CSRF protection in a Rails application?

Rails implements CSRF (Cross-Site Request Forgery) protection through a unique authenticity token. The token is included in forms and verified on each non-GET request. Security considerations involve ensuring the token is present in forms, configuring the protect_from_forgery method appropriately, and using the form_with helper to generate forms with CSRF protection.

5. Explain the concept of Rails Action Cable, and provide examples of scenarios where real-time features, such as chat applications, can benefit from its usage.

Rails Action Cable enables real-time features through WebSockets. It allows bidirectional communication between the client and the server. Real-time chat applications benefit from Action Cable by providing instant message updates without the need for frequent polling, enhancing user experience and engagement.

6. Discuss the differences between a Rails engine and a Rails application, and when would you choose to build and use a Rails engine in your project?

A Rails engine is a smaller, mountable Rails application that can be embedded within another application. It encapsulates functionality and can be shared across projects. Engines are useful for modularizing and reusing code. Choose a Rails engine when you have standalone functionality that can be reused in multiple applications.

7. How can you optimize database queries in a Rails application, and what tools or techniques would you use for profiling and improving query performance?

Optimizing database queries involves strategies like using indexes, minimizing the use of N+1 queries, and leveraging eager loading with includes. Tools like Bullet or QueryTrace can identify and optimize inefficient queries. Active Record's explain method provides insights into query execution plans, helping to fine-tune performance.

8. Explain the purpose of Rails concerns, and provide examples of when and how concerns can be used to enhance code organization and maintainability.

Rails concerns are modules that encapsulate shared behavior and can be included in multiple classes. Use concerns to DRY up code, especially when dealing with cross-cutting concerns like authentication or authorization. For example, a Searchable concern can be used across multiple models to add search functionality.

9. How does Rails handle session management, and what are the security considerations when dealing with user sessions in a web application?

Rails manages sessions using cookies to store session data. The session method provides access to the session hash. Security considerations include using secure and HTTP-only cookies, encrypting sensitive data, and rotating session tokens to mitigate session fixation attacks. The config.session_store option in the config/application.rb file allows configuring session storage mechanisms.

10. Discuss the differences between the before_filter and before_action in Rails controllers, and when would you use one over the other in modern Rails applications?

Both before_filter and before_action are used to execute code before certain controller actions. before_action is the modern syntax, introduced in Rails 4, and is recommended for use. It offers the same functionality as before_filter but aligns with Rails conventions. Use before_action for clarity and consistency in modern Rails applications.