Ruby/Rails Interview Questions

A collection of interview questions about Ruby/Rails.

There is a reason why there are no answers here — you as an interviewee should do your own research about things you don't know or fully understand. Self-study is the best way to learn but it doesn't mean you're on your own, feel free to drop by #ruby or #rubyonrails on Freenode and ask questions.

Ruby

• Compare Symbol and String, why use one vs the other?
• Describe multiple ways to define an instance method in Ruby; now do the similar for class methods
• Which is generally the better option (not only for Ruby): a recursive function or an iterative one?
• What are #method_missing and #send? Why are they useful?
• What are the various Ruby runtimes, and how are they different?
• What does self mean when used in a class?
• What does it mean that "everything in Ruby is an object"?
• What is a Hash? How efficient is reading/writing/iterating over one?
• What is a block? Write a method that takes a block as an argument
• What is the difference between a lambda, a block and a proc?
• What about closures in Ruby? What are they?
• Explain what a ||= b means
• What is memoization? Why and when would you use it?
• Have you heard the term PORO? Do you know what it is?
• Is it bad to rescue Exception? Why?
• What's the difference between the & and && operators?
• What's the difference between the and and && operators? Why use one over the other?
• What is meta-programming, what methods of meta-programming does Ruby support, and when/why would you use it in a project?
• What does the lazy method do to enumerators and why is that useful?
• Why do some methods end with a bang ! and others with question marks ?, what are they called and what do they do?
• Go through Basic OOP primitives like encapsulation, abstraction, polymorphism and inheritance
• Talk about SOLID principle
• What's the difference between extend, prepend, and include?
• Describe access modifiers and how they are used within the ruby language (private, public, protected)
• How would you declare and use a constructor in Ruby?
• How would you create getter and setter methods in Ruby?
• What is a Class, what is an Object and why we need Module?
• Does Ruby support multiple inheritance?
• What are mixins, how do they work, and how would you use them? What are some advantages of using them and what are some potential problems? Give examples to support your answers
• Explain what singleton methods are, what is Eigenclass in Ruby?
• Describe Ruby method lookup path
• Describe available Ruby callbacks and how can we use them in practice?
• Why Enumerable is so useful? Elaborate on methods like .each, .map, .inject, .reject, et cetera (also shortcut notation e.g. .reduce(:+))
• Why would you use BigDecimal over float?
• When do you prefer to use fetch over [] on Hash (and other way around) and why?
• What's the difference between local, @instance, @@class, and $global variables? Why and where would you use specific type?
• How can you implement method overloading?
• How can you call the base class method from inside of its overriden method?

Rails

• Explain the different pieces of Rails
• Explain the processing flow of a Rails request
• Explain MVC in terms of Rails
• What is REST?
• Describe the Rails Asset Pipeline and how it handles assets (such as JavaScript and CSS files); bonus points for explaining what was the big change in Rails 5.1
• What is an ORM?
• What is ActiveRecord and what is Arel? Describe the capabilities of each
• What is the Convention over Configuration pattern? Provide examples of how it is applied in Rails
• What is the fat model, skinny controller approach? Discuss some of its advantages and pitfalls, as well as some alternatives
• Describe the Rails testing philosophy
• What is the purpose of layouts?
• Explain the use of yield and content_for in layouts and provide examples
• What are N+1 queries and how can you avoid them? How would you find/debug N+1 queries?
• What are filters/actions in Rails? Describe the three types of filters, including how and why each might be used, and the order in which they are executed
• What is Rack middleware? How does it compare to controller filters/actions?
• Explain what Rails' mass-assignment vulnerability is and Rails' method to control field access
• How do you sort an Array of objects by a particular attribute? What is a better way to do sorting with ActiveRecord?
• What are the different server options for running a Rails/Rack app?
• Explain CSRF and how Rails combats it
• Explain various forms of caching available in Rails
• How is something like 30.seconds.ago implemented?
• What is Rails concern?
• What is functionality of helpers?
• Which Rails server are you using?
• Which HTML template engine does Rails support?
• What are some ActiveRecords callbacks which you are familiar with?
• Does ActiveRecord have after_delete callback?
• What are the benefits of using active records as opposed to native SQL queries. On which occasion should you be choosing one over the other?
• Explain rails db:migrate and the benefits that comes along with that?
• Explain how Rails' scaffolding works and why you would want to use them
• What is database transactions and how it is represented in Rails?
• Explain ActiveRecord's associations (all of them)
• What are scopes in ActiveRecord? How should you use them?
• Where would you use #pluck and why exactly is it useful?
• Explain eager loading
• How can you eager load associated objects?
• What is difference between render and redirect?
• What is difference between save! and save? (Elaborate on general difference between AR methods with and without a bang !)
• What is difference between form_for and form_tag?
• What is the purpose of environment.rb and application.rb files?
• What is request.xhr?
• How can you list all routes for a Rails application?
• Give an example of nested routes usage
• What is observer in Rails?
• What deployment tools do you use?
• Why do some people say "Rails can't scale"?
• When is Rails a good choice for a project?
• What are some of the drawbacks of Rails?

Meta

Topics below require general Computer Science knowledge that is not tightly coupled with any specific technology stack hence the more you know the better you'll be.

• Algorithms and Data Structures
• Database Design, SQL queries, NoSQL databases
• Testing (TDD/BDD)
• System Design
• DevOps
• Unix knowledge
• Networking
• Application Security

Cracking the Coding Interview is a good resource for high level overview.

References

• https://www.toptal.com/ruby-on-rails#hiring-guide
• https://www.toptal.com/ruby/interview-questions
• https://www.quora.com/How-do-I-prepare-for-an-entry-level-Ruby-on-Rails-developer-interview-What-questions-should-I-expect
• https://github.com/afeld/rails_interview_questions
• https://github.com/rishiip/ruby-on-rails-interview-questions
• https://gist.github.com/ryansobol/5252653
• http://www.rubyinside.com/tips-hiring-ruby-web-developers-4757.HTML
• https://rubygarage.org/blog/how-to-interview-your-ruby-on-rails-developer
• http://anilpunjabi.tumblr.com/post/25948339235/ruby-and-rails-interview-questions-and-answers
• http://career.guru99.com/top-34-ruby-on-rail-interview-questions/
• http://blog.mypath.io/ruby-on-rails-interview-questions-that-will-land-you-the-job/
• https://srikantmahapatra.wordpress.com/2013/11/07/ruby-on-rails-interview-questions-and-answers/
• https://www.codementor.io/ruby-on-rails/tutorial/ruby-on-rails-interview-questions
• http://www.careerride.com/ruby-on-rails-interview-questions.aspx

Contributing

Contributions are welcome. If you would like to correct an error or add new items to the checklist, feel free to create an issue and/or a PR. If you are interested in contributing regularly, drop me a line at the above e-mail to become a collaborator.