21 Ruby on Rails Interview Questions and Answers for 2024

Carefully analyze your job requirements first

You need to create a job post effectively, therefore, focus on the following:

Company descriptions

Introduce your company in a factual yet exciting manner. Explain the growth opportunities, organizational culture, and work environment. Talk about career development opportunities. Finally, explain your compensation and benefits policies.

Job descriptions for Ruby on Rails developers

Explain your job requirements. Mention whether you need them for development projects, maintenance projects, or both. Describe how these projects will help you to meet your organizational objectives. Finally, explain the importance of the contribution of the programmer you are hiring.

Roles and responsibilities of a Ruby on Rails developer

You need an RoR programmer to fulfill the following responsibilities:

• Understand the functional and non-functional requirements;
• Study the technical solutions;
• Create specifications for Ruby on Rails applications;
• Code and unit test new RoR applications;
• Collaborate with the testing and DevOps teams for testing and deployment of new web applications;
• Maintain existing Rails applications;
• Communicate effectively with the relevant stakeholders;
• Participate in continuous improvement projects.

Skills and competencies that you need in an RoR developer

Look for a bachelor’s degree in computer science or related fields when hiring a Ruby on Rails programmer. You should look for the following skills:

• Web development experience with Ruby on Rails;
• Knowledge of Ruby and its syntax;
• Ruby programming language;
• Object-oriented programming skills;
• In-depth understanding of backend development;
• Conceptual understanding of server-side templating languages;
• Knowledge of server-side CSS preprocessors;
• Familiarity with JavaScript, HTML5, CSS3 for front-end development;
• Knowledge of concepts like the Object Relationship Model, “Model View Controller” (MVC), and RESTful APIs;
• Experience with SQL databases and NoSQL databases;
• Knowledge of integrating multiple data sources into apps;
• Understanding of software architecture, testing concepts, and “Continuous Integration” (CI)/”Continuous Delivery” (CD);
• Familiarity with operating systems like Windows, Unix, Linux, etc.;
• Familiarity with cloud platforms;
• Knowledge of a version control system and tools like GitHub;
• Experience with popular test automation frameworks and DevOps tools.

Look for the following competencies:

• Communication skills;
• Problem-solving skills;
• Passion for excellence;
• Commitment to project goals;
• Collaboration skills.

Ruby on Rails interview questions for junior developers

You might need to hire a junior, mid-level, or senior developer. To help you, we have categorized the following Ruby on Rails interview questions accordingly. Skip to whichever type of developer questions you need.

Ask the following interview questions for hiring junior RoR programmers:

Question 1: How do “controllers”, “views”, “helpers”, and “models” vary in the case of Ruby?

Answer: The differences are as follows:

• “Controllers”: This subdirectory has the controller classes.
• “Views”: Views hold the important display templates that are needed to fill the data from the application.
• “Helpers”: Helper modules hold “helper classes”. “Helper classes” facilitate managing other classes.
• “Models”: These hold the classes for modeling the data stored in the database.

Question 2: What does an “Active Record” do in Ruby on Rails?

Answer: An “Active Record” in RoR plays the role of the “Model” (M) in the “Model View Controller” (MVC) in the case of Ruby on Rails. Programmers use this layer to represent the business logic and data.

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“Active Records” in Rails allow developers to create and use business logic-related objects. The data for these objects need persistent storage on a database. “Active Records” help to maintain the relation between an object and the database, furthermore, it helps to perform validations.

Ruby on Rails uses metaprogramming when dealing with “Active Records”. It identifies a column in a schema, and it automatically binds them to the relevant domain objects.

Question 3: How do “Lambdas” and “Procs” differ in Ruby on Rails?

Answer: “Lambdas” help developers define a block and its parameters. “Procs” do the same, however, they use arguments differently. A “Lambda” will check the number of arguments that a program passes to it. A “Proc” will ignore unexpected arguments, and it will assign a “nil” to any missing argument.

“Procs” and “Lambdas” respond differently to “Return” statements. A “Lambda” will pass the control to the calling method in the response to a “Return” statement. However, a “Proc” will return the control immediately. “Procs” don’t go back to the calling method.

Question 4: What does the “Action Controller” do in Ruby on Rails?

Answer: Ruby on Rails supports the MVC design pattern, and the “Action Controller” is the “Controller” (C) in the case of this framework. The router determines the controller it should use while serving a request. The “Action Controller” then understands the request.

It produces the desired output. To do this, the controller receives the request. The controller in Ruby on Rails handles the routing of external requests to internal actions. It then fetches or saves data from a model. The controller then uses a view to create the HTML output. “Action Controllers” act as intermediaries between models and views by making the model data available to Views.

Question 5: Name a few IDEs (Integrated Development Environments) to use with RoR.

Answer: Developers can use the following IDEs:

• Eclipse;
• IntelliJ IDEA;
• Netbeans;
• Komodo;
• Kuso IDE;
• Aptana Studio;
• TextMate;
• Ice Coder;
• RubyMine;
• Arcadia.

Question 6: Name a few methods to install Ruby on Rails.

Answer: Programmers can install the Rails framework using the following methods:

• By using “rbenv”, the popular command-line tool;
• With the help of RVM (Ruby Version Manager), another well-known command-line tool.

Installing RoR from the source is another option, however, installing RoR by using “rbenv” is the best alternative.

Question 7: Provide examples of some Ruby on Rails scripts.

Answer: Developers can use several useful tools to develop RoR apps. The Rails framework provides these tools as command-line scripts, and the following are a few examples:

• Rails Console;
• WEBrick Web Server;
• Generators;
• Rails Migration.

Question 8: Name two differences between Ruby on Rails and Java.

Answer: Ruby on Rails and Java have many differences, and the following are two examples:

• Java is a statically-typed language. On the other hand, Ruby on Rails is based on Ruby, a dynamically-typed language. The type of variable in Ruby is determined only at the runtime.
• Java allows simple inheritance. You can declare which interfaces a class in Java would implement. Ruby allows multiple inheritances though.

Question 9: What does Embedded Ruby (ERB) do?

Answer: Ruby developers might use templating languages, and ERB is a templating language. Programmers can add actual Ruby code to plain text documents using ERB, furthermore, they can put such pieces of code into HTML files.

They can then generate documents that provide information about the app, e.g., documents that describe the program flow. Developers find ERB easy to use. Furthermore, they can use ERB-related tutorials on the Ruby documentation website.

Question 10: Explain the naming conventions used in Ruby on Rails

Answer: Ruby on Rails developers use the following naming conventions:

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• Use lowercase letters for class variables, and separate the words with underscores.
• Start each word in classes and modules with an uppercase letter. Use mixed case letters, and don’t use underscores.
• Use lowercase letters and underscores between words while naming database tables, furthermore, utilize plural forms.
• Use unbroken mixed-case letters to name models, and have a singular form with the database table name.
• Use the plural form to name the Rails controller classes.

Question 11: Mention the syntax to define instance variable, a global variable, and a class variable in Ruby.

Answer: You should define them as follows:

• Start an instance variable with “@”.
• Start a class variable with “@@”.
• Begin a global variable with “$”.

Question 12: Mention the syntax to define a “controller” in Ruby on Rails.

Answer: You should define a “controller” in the following way:

class ClientsController < ApplicationController
 def new
 end
end

Question 13: When do we use self in Ruby?

Answer:  Self is used for defining and calling class methods. An instance calls a class method as self.class.method.

Question 14: What is the difference between dynamic and static scaffolding?

Answer: Dynamic Scaffolding automatically generates the entire content and user interface at runtime. Static Scaffolding requires the insertion of the command to generate the data with their fields.

Ruby on Rails interview questions and answers for mid-level developers

Use the following interview questions when hiring mid-level Ruby on Rails developers:

Question 15: What design patterns can you use with Ruby on Rails apart from MVC?

Answer: The Ruby on Rails framework supports the MVC (Model View Controller) design pattern, however, developers might need more sometimes. They might need additional design patterns due to the following reasons:

• Views should present information. However, they sometimes become very large due to business logic.
• Controllers should only hold information that’s required to do their work. However, they often hold a lot more information.

Ruby on Rails experts created two design patterns to address these. These are as follows:

• The presenter pattern;
• The service object pattern.

Implement the presenter pattern by doing the following:

• Keep HTML, CSS, and ERB (Embedded Ruby) in Views. Avoid keeping “Active Record” queries in views.
• Avoid including business logic in views. Use “Helpers” to handle business logic-related code instead.
• Use arguments to pass input to “Helper” methods instead of instance variables of a Ruby class.

Implement the service object pattern by doing the following:

• Avoid overcrowding the controllers. Keep only the information that instructs other elements. Delegate all other instructions to service objects.
• Save service objects under the “app/services” folders. The “autoloading” feature of Ruby on Rails will load everything from the “app/” folders. Therefore, the code in the service objects will be available to controllers.

Question 14: Explain how to secure your Ruby on Rails app from CSRF (Cross-Site Request Forgery) attacks.

Answer: Among various forms of cyber-attacks, CSRF attacks can often compromise web apps. A hacker submits a page request on behalf of a user of your web app to a different website. These attacks can expose the sensitive data on your web app to cyber criminals.

Ruby on Rails allows you to add the “protect_from_forgery” value to the “ApplicationController” of your app, which prompts RoR to require a CSRF token. Every form that the Rails framework creates will have this token as a hidden field. This prevents CSRF attacks.

Question 15: How do “Observers” in Ruby on Rails differ from “Callbacks”?

Answer: “Callbacks” in Ruby on Rails are methods. The program can call these methods at specific moments of the lifecycle of an object. E.g., a program might call these methods when validating an object. It might call them at the time of creating, updating or deleting an object.

“Observers” in Ruby on Rails have many similarities with “callbacks”. These are methods too. However, the Rails framework uses them when the method isn’t associated directly with the lifecycle of an object.

A program might call an “observer” when it displays values from a model in the UI. It can call an “observer” when updating a model from the user input. “Observers” live longer than “callbacks”.

Question 16: Provide a few examples of using a “subdirectory” in Ruby on Rails.

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Answer: The following are a few examples:

• The “App” directory: It loads with all subdirectories that are required for your Ruby on Rails application.
• “App”/”controllers”: When a user makes a web request, the “controller” handles it. The Rails framework looks for the “controller” classes in the “controller subdirectory”.
• “App”/”Helpers”: The Ruby on Rails framework uses a “helpers subdirectory”, which holds the helper classes. These classes help the view, model, and controller classes to function.

Question 17: What is a “Rake” in Ruby on Rails?

Answer: Ruby on Rails uses “Rake”, a Ruby utility. Its function is the same as the Unix utility “Make”. The “Rake” utility in Ruby uses a “Rakefile” and “.rake files” to create a list of tasks.

The Rails framework utilizes the “Rake” utility for various administrative tasks, e.g., migrating a database by using a script. Another example where it uses a “Rake” is to load a schema into a database.

Senior Ruby on Rails developer interview questions

Check out the following questions when interviewing senior Ruby on Rails developers:

Question 18: Provide one example where garbage collection issues might cause security issues in a Ruby on Rails app.

Answer: Garbage collection in an RoR app ensures the removal of pointer values after the execution of a program. It removes objects that are not used from the memory.

However, Ruby has two types of symbols. They are as follows:

• Immortal symbols: Ruby creates them when the code is dynamically modified. The garbage collection process of Ruby doesn’t work on them.
• Mortal symbols: These are symbols created in all other cases, and the garbage collection process covers them.

If a program created immortal symbols from user inputs, then it’s risky. Garbage collection will not work. A large number of immortal symbols will be created. Hackers can launch a DoS (Denial of Service) attack by flooding the web-client app with unique string keys.

Question 19: What do “mixins” do in Ruby?

Answer: Ruby offers a feature called “mixins”. Some programming languages allow a Ruby class to inherit features from multiple parent classes. Ruby doesn’t allow it, however, it allows “mixins” instead of that. “Mixins” are pieces of code included within a module.

“Mixins” in Ruby enable modules to access instance methods of other modules. They do that by using the “include” method, which provides a controlled way to add functionalities to classes. A class can include a “mixin”. It can extend it too, and a class might contain multiple “mixins”.

Question 20: State where Ruby on Rails might not be the best choice of the development framework.

Answer: Do you plan to create a web application with CRUD (Create-Read-Update-Delete) operations on a database, and do you intend to use the MVC pattern? Ruby on Rails works very well. However, it won’t work well in the following instances:

• You need foreign keys in databases.
• The application needs to link with many databases simultaneously.
• You need to use SOAP web services.
• The application needs to establish connections with multiple database servers simultaneously.

Question 21: Can a Ruby on Rails application run without creating a database?

Answer: A developer can do this by uncommenting the following lines in “environment.rb”.

Path=> rootpath conf/environment.rb
config.frameworks = [ action_web_service, :action_mailer, :active_record]

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