40+ Frequently Asked Ruby on Rails Interview Questions and Answers [2023]

Ruby on Rails is probably the most famous Ruby framework. Its simplicity of use, MVC architecture, community, and scalability are the reasons for its popularity.

Some of the big names that use Ruby on Rails are GitHub, Dribble, Shopify, Airbnb, Etsy, Kickstarter, Twitch, and Zendesk, to mention a few. 

If you are an intermediate or skilled Ruby on Rails engineer, understanding the nature of questions you are likely to find in your next interview is a smart move. 

Interviews can be scary if you are unprepared. However, if you are well prepared, your confidence will shoot up, and you might be lucky to land a new role in your dream company. 

These are some common Ruby on Rails interview questions and their answers. 

What is Ruby on Rails?

Ruby is an object-oriented programming language with a simple syntax.

Ruby on Rails is a Ruby framework that developers use to create web applications. 

Discuss the advantages of Ruby on Rails

• Less code than other languages: You can achieve a lot with just a few lines of code with Rails.
• Extensive library and gems: There exist tons of libraries and gems to improve the functionality of a Ruby on Rails app. 
• Easy to learn: Ruby on Rails’ code looks like plain English.
• A big community.

Discuss the limits of Ruby on Rails

• When compared with Django and Node.js, Rails’ runtime speed and performance are low. 
• Limited documentation for some of its gems. 
• Ruby on Rails is opinionated, which limits a developer’s flexibility. 

What is a Rails controller?

It is the logical center of a Ruby on Rails application. Rails controller manages, coordinates, and monitors all the interactions between users, models, and views. 

What is Rails’ Active Record?

Active Record is an object relation mapping (ORM) technique. This layer of Ruby code runs between the code logic and your database. After you write Ruby code, you run ‘migrations’ to make changes to your database. 

What is MVC, and how does it work?

The model-view-controller (MVC) architectural pattern separates the business logic from the input and presentation logic. 

• Model: handles all the data logic in a Rails app.
• View: this is part of the application that users view.
• Controller: is like a bridge or broker that allows the model and view to communicate. 

What is an action controller in Ruby on Rails?

The Action Controller is the C in the MVC pattern. The Action Controller receives incoming requests, makes sense of the request, and produces the appropriate output. 

What is rake in Rails?

Rake is a task runner for Ruby on Rails and Ruby applications. Rails have predefined Rake tasks for performing tests, running migrations, and creating databases. 

What is yield in Ruby on Rails?

Yield is a keyword used inside methods to call a block. There is no limitation to the number of arguments Yield can pass to the block. Blocks, in this case, are methods without names that are passable as extra arguments to other methods. 

What is Garbage Collection Ruby on Rails?

Garbage Collection is the process of controlling memory used by computer programs. Ruby on Rails keeps track of what objects are being used by the program rather than the programmer. The developers can thus focus on logic and convention instead of worrying about memory allocation. 

What is the role of Garbage Collection in the Rails app?

It frees up memory on your machine for other processes to execute. Garbage collection achieves this by removing inaccessible objects that a program leaves after execution. 

What is an asset pipeline?

An Asset Pipeline in Ruby on Rails provides a framework that minifies and concatenates CSS and JavaScript assets. This framework allows all the assets in your Rails app to be automatically combined with assets from other gems. 

Differentiate between dynamic and static scaffolding

Scaffolding is the process of generating major parts of Rails application. 

Static scaffolding explicitly enters a command that produces the required data in respective fields. To complete static scaffolding, you must run migrations.

Dynamic scaffolding generates contents and user interfaces during runtime. This process can be used to create, modify and delete actions in a Rails app. 

What is a class library?

A class library comprises domains in Ruby on Rails, and thread programming and data types are examples of such domains. A class library allows a developer to create code abstraction and thus use the same logic within different elements in an app. 

Describe Polymorphic Association in Rails

Polymorphic Association is a type of Active Record Association. Polymorphism means that an object can have many forms. In the Rails context, Polymorphic Association allows you to define a single model that can be associated with or belong to other models without writing a repeat code. 

What is String Interpolation in Ruby?

String Interpolation is adding placeholders referencing other values in a string object. The use of the addition operator is the simplest way to interpolate values.  

Consider this example:

name = "Titus"

puts "Hello "   name

The output will be;

Hello Titus

What is Object Relationship Model (ORM)?

An ORM is a bridge between databases and object-oriented programs. An object relationship, in Rails, indicates when classes are being mapped to a table within your database. 

Explain Rails migration

Migrations help developers to make changes to a database schema conveniently. Developers can thus manage rollout and rollback in the database schema in a controlled environment. This approach prevents you from managing individual SQL scripts to define your changes. 

Explain the naming convention in Rails

• Class and module: use MixedCase but don’t have an underscore. Names in classes and modules start with an uppercase letter.
• Database table: name of a database table should be in plural and snake-case. 
• Variables: letters declaring variables should be in lowercase and snake_case with an underscore separating them. 
• Model:  use MixedCase to specify a model and ensure the name is in the singular form. 
• Controllers: controller names are pluralized. 

What is the difference between string and text in Rails?

:string is suitable when you want to store short text with up to 255 characters. You can use it with names, usernames, emails, passwords, and titles. 

:text fits long descriptions. Perfect examples of comments on a blog post or a store description. 

class CreatePosts < ActiveRecord::Migration

   def self.up

      create_table:posts do |t|

         t.string:description

         t.text :content 

      end

   end

Explain Cross-Site Request Forgery (CSRF)

Cross-Site Request Forgery (CSRF) is an online attack where attacker traps authenticated users to perform certain actions on their behalf. 

Rails require developers to add “protect_from_forgery” to the ApplicationController to avoid CSRF attacks. The app will always require a CSRF token to authenticate a user. 

Explain what mixin is in Rails

A mixin offers a controlled way of adding functionalities to a class. Many different mixins make up a class. Mixins eradicate the need to have multiple inheritances. 

What is the use of load and require in Ruby?

require( ) is used to import libraries/gems

load() is used to execute a block of code

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

Rails observers are used when a method is not directly related to the lifecycle of an object. Their lifecycles are big, and they can be attached or detached at any time.

Callbacks can only be called at specific instances in the lifecycle of an object. Examples of such instances are updates, creation, and validation. Callbacks are only active for short periods. 

What are Harnesses and Fixtures in Ruby?

Fixtures refer to a way of organizing data that you want to test. They can be created in files that end with a .yml extension. 

Harnesses is the environment or test runner for running Rails tests. Fixtures are set up in Harnesses. 

What is the difference between extend and include?

“Include” adds an instance method to a class. The code will thus be accessible via class methods.

“Extend” adds instance methods defined in the module to the extended class. 

Are gems and plugins the same in Ruby?

Gems are packaged Ruby applications that need to be installed. They are general-purpose and don’t depend on Rails for functionality. 

Plugins in Ruby on Rails are deployed together with your Rails application. They modify or add to the core functionality of Rails. 

What are rail observers?

Rails observer offers a mechanism where one object informs the others when its state changes. It is applicable in a one-to-many relationship such that when one object changes, all the dependent objects are informed and changed automatically. 

What command is used to create a migration?

bin/rails db:migrate

Show how to define class, Instance, and global variables in Ruby

• Class variables: Can be used anywhere within their class. The class descendants can also access them. They start with @@. 
• Instance variables: Used in the local scope that is specific to the created object’s instances. They may vary from one object to another. They start with @. 
• Global Variables: Accessible anywhere within the program. Starts with $. 

Which role does rakefile available in the demo directory in Ruby play?

Rakefile helps with the testing and packaging of Rails code. The file defines the tasks that perform tests or demonstrate the application’s features. 

What is a sweeper in Rails?

Sweepers act as terminators in caching. They act as half-filters and half-observers and implement callbacks for the two roles. The ‘expire_cache’ finds all the cache fragments that need to be expired and clears them, 

What are filters?

These are methods “before”, or “after” a controller’s action is executed. Such methods are inherited and will run with every request your app receives as long you have set them in the ApplicationController. 

Differentiate between redirect and render in Rails

Render: used to render a template and then send it to the client in response to the request. This template then generates the page that the browser will display. 

Redirect: sends a new HTTP request to a different URL. This action redirects the client to a different controller or action. This method comes in handy when you want to change the URL clients see on the browser. 

Differentiate between calling super() and super call

• Super: sends a message to the current object’s parent to invoke all arguments of the invoked method. 
• super():  does not send any arguments to the parent. 

What is the difference between Procs and Blocks?

• Blocks: A piece of code surrounded by do/end statements or curly braces. They are created and executed each time the method is called. 
• Procs: Blocks of code bound together to a set of local variables. This code can be called in different contexts and still accesses the variables. 

What is the difference between puts and print statements?

We use puts when we want to print something on the screen. For example, 

puts “Hello World!!!”

Prints Hello World!!! on the screen

We use print when we don’t want to add a new line on the console. 

print “Hello World!!!” 

Outputs Hello World!!!, but a new line will not be added to the console. 

What are dynamic finders?

Dynamic finders allow developers to search for records in their database without using raw SQL queries. They use the find_by_ keyword, which is then followed attribute to be searched. 

Explain how Rail implements ajax

• A trigger, such as submitting a form or clicking a button, is initiated.
• JavaScript method sends the trigger data to a handler in the server.
• The handler on the server-side works on the data and sends HTML to the web client.
• JavaScript handler on the client side receives HTML content and updates the current page. 

Explain Dig, Float, and Max

• With the Dig method, you can extract values from nested hashes or arrays. 
• Float is a Ruby data type representing real numbers with floating-point precision.
• Max is a method that can be used with arrays and hashes. It returns the maximum value in a collection of items/values. 

array = [2, 9, 4, 7, 3]

maximum = array.max

The console will output 9 as it is the biggest number. 

Conclusion

Above are some questions you will likely find in your next Ruby on Rails. If you are an all-rounded software engineer, check these Node.js interview questions. Ensure that you understand the job description of a Rails engineer before you attend your next interview.