Question 1

What is the difference between a local variable and an instance variable in Ruby?

Accepted Answer

A local variable starts with a lowercase letter or underscore and is only accessible within its scope (method or block). An instance variable starts with @ and is accessible in all methods of the object, persisting throughout the instance's lifetime. This distinction is fundamental for state management in Ruby objects.

Question 2

How to define a class in Ruby?

Accepted Answer

In Ruby, a class is defined with the class keyword followed by the class name (CamelCase by convention) and ends with end. The initialize method serves as the constructor and is automatically called when creating a new instance with Class.new. Instance variables (prefixed with @) store the state of each object.

Question 3

What does the acronym MVC stand for in the context of Rails?

Accepted Answer

MVC stands for Model-View-Controller, an architectural pattern that separates the application into three interconnected components. The Model handles data and business logic, the View displays the user interface, and the Controller orchestrates interactions between the two. This separation facilitates code maintenance and testing.

Question 4

In a Rails application, where is the main route configuration file located?

Accepted Answer

The config/routes.rb file is the central point for defining all routes in a Rails application. This file maps incoming URLs to their corresponding controllers and actions. Rails reads this file at application startup to build the routing table that determines how each HTTP request will be handled.

Question 5

What is Devise in the Rails ecosystem?

Accepted Answer

Devise is a flexible and complete authentication gem for Rails, built on Warden. It provides pre-configured modules to handle registration, login, password recovery, email confirmation, account locking and more. Devise is the most popular authentication solution in the Rails ecosystem due to its ease of integration and modularity.

Question 6

What is the default asset management system in Rails 7+?

Accepted Answer

Importmap-rails is the default system in Rails 7+ for managing JavaScript files. It allows using native ES modules directly in the browser without a bundling step, by mapping package names to CDN URLs or local files. This significantly simplifies frontend configuration while eliminating the Node.js dependency.

Question 7

Which command creates a new Rails application in API-only mode?

Accepted Answer

The --api flag when creating a Rails application generates a lightweight application optimized for APIs. This configuration excludes view-related middlewares (cookies, sessions, flash), doesn't include Action View and Action Cable by default, and configures ApplicationController to inherit from ActionController::API rather than ActionController::Base. This reduces application size and improves performance for pure API use cases.

Question 8

What is a Rails Engine?

Accepted Answer

A Rails Engine is a miniature Rails application that can be mounted within a host application. It allows sharing code (models, controllers, views, routes) between multiple applications or creating isolated and reusable features. Gems like Devise, Sidekiq Web UI and ActiveAdmin are examples of popular engines used in the Rails ecosystem.

Question 9

What is the main purpose of adding an index on a database column?

Accepted Answer

An index speeds up search queries by creating an optimized data structure (usually a B-tree) that avoids scanning all rows in the table. Without an index, the database performs a sequential scan which can be very slow on large tables. Columns frequently used in WHERE clauses, ORDER BY or joins are ideal candidates for indexing.

Question 10

What is a Service Object in Rails?

Accepted Answer

A Service Object is a plain Ruby class (PORO) that encapsulates complex business logic, typically a single operation. It extracts logic from controllers and models to maintain the Single Responsibility Principle (SRP). Typically, a service object exposes a single public method like call or execute, making it easy to test and reuse.

คำถามสัมภาษณ์ Ruby on Rails

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สำรวจหัวข้อ Ruby on Rails ทั้งหมด

Ruby Basics

Ruby Object-Oriented Programming

Rails Fundamentals

Routing & Controllers

ActiveRecord Basics

Views & ERB Templates

ActiveRecord Associations

Advanced ActiveRecord Queries

Rails Forms

Authentication & Authorization

Modern Asset Pipeline & Frontend

Rails API Mode

Testing with RSpec

ActiveJob & Background Jobs

ActionCable & WebSockets

ActionMailer

ActiveStorage

Caching Strategies

Advanced Migrations

Rails Engines & Modular Apps

Performance Optimization

Rails Design Patterns

Ruby Metaprogramming

Rails Security

GraphQL with Rails

Deployment & Production

Monitoring & Logging

Rails Upgrade Strategies

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