Ruby on Rails Interview Questions and Answers — Controller — Part 1

9 min readOct 15, 2023


  • What is the role of a controller in a Ruby on Rails application?
  • How does routing work in Rails, and how are URLs mapped to controller actions?
  • Explain the concept of RESTful routing and its benefits in Rails controllers.
  • What are strong parameters in Rails controllers, and why are they necessary?
  • How do you define custom controller actions in Rails, and when would you use them?

1. What is the role of a controller in a Ruby on Rails application?

The controller is one of the fundamental components that play a crucial role in the Model-View-Controller (MVC) architectural pattern. Its primary role is to handle incoming HTTP requests from clients (usually web browsers or API consumers), process those requests, interact with the model (database), and return an appropriate response to the client.


The controller is responsible for routing incoming HTTP requests to the appropriate action method within the controller based on the URL and HTTP verb (GET, POST, PUT, DELETE, etc.). This is typically defined in the application’s route configuration.

Request Handling

When a request is routed to a controller, the controller’s action method is responsible for processing the request. It can access parameters sent with the request (e.g., form data, query parameters, or route parameters) and use them to determine what needs to be done.

Business Logic

Controllers often contain the application’s business logic, determining how to handle the request. This can involve querying the database through the model, performing calculations, or invoking other services.

Interaction with Models

Controllers communicate with the model layer to perform CRUD (Create, Read, Update, Delete) operations on the database. They use model classes to create, read, update, or delete records in the database.

Rendering Views

After processing a request and interacting with the model as needed, the controller is responsible for rendering the appropriate view. Views are templates written in HTML with embedded Ruby code (ERB) that can display data to the user.

Handling Responses

Controllers are responsible for constructing HTTP responses to send to the client. This includes setting HTTP status codes, headers, and sending the rendered view or JSON data, depending on the nature of the request.

Handling Redirects

Controllers can also issue redirects when necessary, such as after a successful form submission or when authentication is required.

Here’s a simplified example of a Rails controller action:

class UsersController < ApplicationController
def show
@user = User.find(params[:id]) # Retrieve a user from the database

def create
@user = # Create a new user object
redirect_to @user # Redirect to the user's profile page on success
render 'new' # Render the 'new' view on failure

In this example, the UsersController handles actions related to user profiles and user creation, including retrieving user data from the model, creating new user records, and rendering views or redirecting as needed.

2. How does routing work in Rails, and how are URLs mapped to controller actions?

Routing in Ruby on Rails is the process of mapping incoming HTTP requests (URLs) to controller actions. It determines which controller and action should handle a particular request based on the URL’s path and HTTP method. Rails provides a robust routing system that is defined in the config/routes.rb file of your application.

Routes Configuration

In the config/routes.rb file, you define the routes for your application using a domain-specific language provided by Rails. You can specify routes using the get, post, put, patch, delete, or resources methods, among others.

# Example routes.rb
Rails.application.routes.draw do
get 'articles' => 'articles#index'
get 'articles/:id' => 'articles#show'
post 'articles' => 'articles#create'

Mapping URLs to Controller Actions

Each route definition specifies a URL pattern and maps it to a controller and an action. For example, in the code above:

  • GET /articles would be handled by the index action of the ArticlesController.
  • GET /articles/:id (where :id is a dynamic parameter) would be handled by the show action of the ArticlesController.
  • POST /articles would be handled by the create action of the ArticlesController.

Dynamic Parameters

You can define dynamic segments in routes by using :param_name, which allows you to capture values from the URL and pass them as parameters to controller actions. For example, in the route get 'articles/:id' => 'articles#show', :id is a dynamic parameter that gets passed to the show action as a parameter.

Named Routes

You can also give routes names to make it easier to generate URLs within your application. For example:

Rails.application.routes.draw do
get 'articles' => 'articles#index', as: 'articles_list'

Now, you can use articles_list_path or articles_list_url in your application to generate URLs for the articles#index action.

Resourceful Routing

Rails provides a convenient way to define RESTful routes using the resources method. It automatically generates a set of routes for CRUD operations on a resource, including index, show, new, create, edit, update, and destroy actions.

resources :articles

This single line of code generates all the routes needed for a typical resource, mapping URLs like /articles and /articles/1 to their respective controller actions.

Route Helpers

Rails generates helper methods for each defined route, making it easy to generate URLs within your application. For example, if you have get 'articles' => 'articles#index', Rails will create a helper method called articles_path or articles_url.

3. Explain the concept of RESTful routing and its benefits in Rails controllers

RESTful routing is an architectural style for designing networked applications, and it’s particularly well-suited to web applications. In Ruby on Rails, RESTful routing is a key concept that promotes the use of standardized URL patterns and HTTP methods to interact with resources. It encourages a clean and organized way to define routes and controller actions. Here’s an explanation of RESTful routing and its benefits in Rails controllers:

Resource-Oriented Approach

In RESTful routing, everything is treated as a resource. Resources are the central entities in your application, such as users, articles, or products. Each resource is associated with a set of standard CRUD (Create, Read, Update, Delete) actions.

Standard URL Patterns

RESTful routes adhere to standard URL patterns based on HTTP methods, making it easy to understand and predictable. The most common resource-based routes include:

  • GET /resources for listing all resources.
  • GET /resources/:id for displaying a specific resource.
  • GET /resources/new for displaying a form to create a new resource.
  • POST /resources for creating a new resource.
  • GET /resources/:id/edit for displaying a form to edit an existing resource.
  • PUT/PATCH /resources/:id for updating an existing resource.
  • DELETE /resources/:id for deleting an existing resource.

Simplified Controller Actions

With RESTful routing, Rails controllers often follow a standard set of action names, such as index, show, new, create, edit, update, and destroy. This convention simplifies controller code and makes it more maintainable.

Route Helpers

RESTful routes generate route helpers, making it easy to generate URLs and links in your views and controllers. For example, if you have a resource called articles, Rails automatically generates helpers like articles_path and article_path.

Improved Readability

RESTful routes are highly readable and self-explanatory. When you see a URL like /articles/1/edit, you can immediately understand that it's for editing an article with the ID of 1.


RESTful routing encourages a consistent approach to handling resources throughout your application. This consistency can improve code maintainability and developer productivity.


RESTful routing scales well as your application grows. It provides a structured way to manage complex interactions with resources.

Built-in HTTP Semantics

By aligning with HTTP methods (GET, POST, PUT, PATCH, DELETE), RESTful routing leverages the full capabilities of the HTTP protocol, improving the efficiency and performance of your application.

Here’s an example of how RESTful routing is defined in Rails:

# config/routes.rb
resources :articles

With this single line of code, you get all the standard routes for managing articles. You can then define corresponding controller actions (index, show, new, create, edit, update, destroy) in your ArticlesController.

4. What are strong parameters in Rails controllers, and why are they necessary?

Strong parameters in Ruby on Rails controllers are a security feature that helps protect your application from mass assignment vulnerabilities and ensures that only permitted parameters are accepted and processed when creating or updating records in the database. They are necessary to enhance the security and robustness of your Rails application.

Mass Assignment Vulnerabilities

In Rails, it’s common to use hashes or parameters from incoming requests to create or update records in the database. This process is known as mass assignment. Without proper protection, an attacker can potentially manipulate the request parameters to set attributes they shouldn’t have access to, such as administrative privileges or other sensitive data.

Parameter Whitelisting

Strong parameters provide a mechanism to whitelist the specific parameters that are allowed to be used for mass assignment. By explicitly stating which parameters are permitted, you prevent attackers from injecting unexpected or malicious data into your models.

Controller Layer

Strong parameters are typically defined within your controller actions. You specify which parameters are allowed for each action, usually within a private method called params.require and permit. For example:

def create
@article =
# ...


def article_params
params.require(:article).permit(:title, :content)

In this example, only the :title and :content parameters are permitted for mass assignment when creating a new Article record.

Improved Security

By explicitly whitelisting parameters, strong parameters protect against unauthorized attribute assignment, reducing the risk of security breaches and data corruption.

Readable and Maintainable Code

Strong parameters make your code more readable and maintainable. Developers can clearly see which attributes are accepted and controlled by each action, improving code documentation and teamwork.

Preventing Unintended Behavior

Without strong parameters, it’s easier to accidentally assign and update attributes that shouldn’t be exposed to the user or external input, leading to unintended behavior or security vulnerabilities.

Adherence to Best Practices

Using strong parameters is considered a best practice in Rails development for ensuring data integrity and security. Many Rails applications have sensitive data, and strong parameters help protect that data.

5. How do you define custom controller actions in Rails, and when would you use them?

In Ruby on Rails, you can define custom controller actions to handle specific HTTP requests and perform custom logic beyond the standard CRUD (Create, Read, Update, Delete) actions. Custom controller actions allow you to tailor your application’s behavior to unique requirements. Here’s how you define and use custom controller actions in Rails:

Define a Custom Action

To define a custom controller action, you need to add a new method in your controller class. This method will handle the custom logic associated with the action. Here’s an example of defining a custom action called search in an ArticlesController:

class ArticlesController < ApplicationController
# Other actions (e.g., index, show, create, update, destroy)

def search
# Custom logic for the search action

Set Up a Route

To access the custom action via a URL, you need to define a corresponding route in the config/routes.rb file. You can use the get, post, or other HTTP verb methods to map a URL to the custom action. For example:

# config/routes.rb
get 'articles/search', to: 'articles#search'

This maps a GET request to the URL /articles/search to the search action in the ArticlesController.

Implement Custom Logic

Inside the custom action method, you can implement the specific logic required for that action. This can include querying the database, performing calculations, rendering a different view, or responding with JSON data. Custom actions are versatile and can accommodate a wide range of application-specific functionality.

def search
@search_results = Article.where("title LIKE ?", "%#{params[:query]}%")
render 'search_results' # Render a custom view

Use the Action

Once you’ve defined the custom action and route, you can access it through the corresponding URL. In this example, you can access the search action by visiting /articles/search in your web browser.

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