Ruby on Rails Interview Questions and Answers — View — Part 2

9 min readNov 19, 2023


Ruby on Rails Interview Questions and Answers — View — Part 2
  • What are partials in Rails views, and why would you use them?
  • How do you handle forms and user input in Rails view?
  • What is the purpose of form helpers like form_for and form_tag in Rails view?
  • How can you include JavaScript or CSS files in a Rails view?
  • What is the asset pipeline in Ruby on Rails, and why is it important?

6. What are partials in Rails views, and why would you use them?

The partials are a way to break up a view into smaller, reusable components. They are essentially snippets of code that can be included in other views. Partials are especially useful when you have repetitive elements in your views or when you want to modularize your code for better maintainability and readability.

Creating Partials

Partials are typically named with a leading underscore (e.g., _partial_name.html.erb).You can create partials for specific elements, such as a form, a list, or any other piece of HTML.

Rendering Partials

To render a partial within a view, you can use the render method with the :partial option.

<%= render partial: 'shared/header' %>

Local Variables

You can pass local variables to partials, allowing them to customize their behavior based on the context in which they are rendered.

<%= render partial: 'shared/header', locals: { title: 'Page Title' } %>


Partials can also be used to render collections of objects.

<%= render partial: 'products/product', collection: @products %>

This would render the _product.html.erb partial for each item in the @products collection.

Code Reusability

Partials promote code reusability by allowing you to define common components in one place and reuse them across multiple views. This helps in maintaining a DRY (Don’t Repeat Yourself) codebase.


Partials encapsulate logic related to a specific component, making it easier to understand and maintain.

Here’s an example to illustrate the use of partials. Suppose you have a blog application with comments, and you want to display comments on both the blog post page and the user profile page. Instead of duplicating the code for rendering comments in both views, you can create a _comment.html.erb partial and render it in both places, reducing redundancy and improving maintainability.

# app/views/posts/show.html.erb
<%= render partial: 'comments/comment', collection: @post.comments %>

# app/views/users/show.html.erb
<%= render partial: 'comments/comment', collection: @user.comments %>

7. How do you handle forms and user input in Rails view?

Handling forms and user input in Rails views involves creating HTML forms, incorporating Rails form helpers, and processing the submitted data in the corresponding controller.

Create a Form in the View

a. Using form_for Helper

Rails provides a powerful form_for helper that simplifies form creation.

# app/views/posts/new.html.erb

<%= form_for @post do |f| %>
<!-- Form Fields -->
<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :content %>
<%= f.text_area :content %>

<!-- Submit Button -->
<%= f.submit "Create Post" %>
<% end %>

@post is an instance variable assigned in the controller, representing the post you want to create.

b. Using form_tag for Non-Model Forms:

If your form is not tied to a model, you can use form_tag instead.

# app/views/pages/contact.html.erb

<%= form_tag('/contact') do %>
<!-- Form Fields -->
<%= label_tag :email, 'Email:' %>
<%= text_field_tag :email %>

<%= label_tag :message, 'Message:' %>
<%= text_area_tag :message %>

<!-- Submit Button -->
<%= submit_tag "Send Message" %>
<% end %>

Handle Form Submission in the Controller

a. Create Action
Define the corresponding action in the controller to handle the form submission.

# app/controllers/posts_controller.rb

class PostsController < ApplicationController
# ...

def create
@post =

redirect_to @post, notice: 'Post was successfully created.'
render :new


def post_params
params.require(:post).permit(:title, :content)

Ensure that you have the necessary strong parameters defined to permit the required attributes.

b. Non-Model Action

For non-model forms, you can access the form data using params directly.

# app/controllers/pages_controller.rb

class PagesController < ApplicationController
# ...

def contact
email = params[:email]
message = params[:message]

# Process the data as needed

redirect_to root_path, notice: 'Message sent successfully.'


a. Model Validation

If you’re working with a model-backed form (e.g., form_for @post), leverage model validations for data integrity.

# app/models/post.rb

class Post < ApplicationRecord
validates :title, presence: true
validates :content, presence: true

b. Displaying Validation Errors

To display validation errors in the view, you can use @model.errors within the form.

<% if @post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>

<% @post.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
<% end %>

Flash Messages

Consider using flash messages to provide feedback to the user after form submission.

# app/controllers/posts_controller.rb

class PostsController < ApplicationController
# ...

def create
@post =

redirect_to @post, notice: 'Post was successfully created.'
render :new

# ...
# app/views/layouts/application.html.erb

<% flash.each do |key, value| %>
<div class="flash-<%= key %>">
<%= value %>
<% end %>

CSRF Protection

Rails provides Cross-Site Request Forgery (CSRF) protection by default. Ensure that your form includes the CSRF token.

<%= csrf_meta_tags %>

8. What is the purpose of form helpers like form_for and form_tag in Rails view?

In Ruby on Rails, form helpers like form_for and form_tag are provided to simplify the process of creating HTML forms in views. These helpers generate HTML form elements and handle various aspects of form submission, making it easier for developers to work with forms and interact with the underlying models or controllers.

form_for Helper

Model-Backed Forms: form_for is primarily used for creating forms that are associated with a specific model. It establishes a connection between the form and the model, simplifying the process of creating, updating, and deleting model records.

<%= form_for @post do |f| %>
<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :content %>
<%= f.text_area :content %>

<%= f.submit %>
<% end %>

Automatic URL Generation: It automatically generates the correct URL for form submission based on the model instance (@post in this case).

Automatic Hidden Field for CSRF Protection: It includes a hidden field with the CSRF token to protect against cross-site request forgery.

form_tag Helper

Non-Model Forms: form_tag is used when creating forms that are not directly tied to a model. This helper is more flexible and is suitable for situations where the form data doesn't correspond directly to a model instance.

<%= form_tag('/search', method: 'get') do %>
<%= text_field_tag :query %>
<%= submit_tag 'Search' %>
<% end %>

Manual URL Specification: You need to manually specify the URL for form submission.

No Automatic Model Binding: Unlike form_for, form_tag doesn't have an implicit connection to a model, so you handle the form data directly in the controller.

General Benefits of Form Helpers

Abstraction of HTML Details: Form helpers abstract away the low-level details of HTML form elements, making it easier for developers to focus on the application logic without having to write HTML code manually.

Consistent and DRY Code: Form helpers promote consistency and adhere to the DRY (Don’t Repeat Yourself) principle. They help avoid duplication of code and reduce the likelihood of errors.

Integration with Rails Features: Form helpers seamlessly integrate with other Rails features, such as model validations, CSRF protection, and routing. This integration simplifies common tasks associated with form handling.

Readability and Maintainability: The use of form helpers enhances code readability and maintainability. The code becomes more concise and expressive, making it easier for developers to understand and collaborate on the codebase.

Automatic Inclusion of Required Elements: Form helpers automatically include elements like CSRF tokens, making the generated forms more secure by default.

Form helpers in Rails, such as form_for and form_tag, provide a higher-level abstraction for working with forms, making it more convenient for developers to create and manage forms in a Rails application. These helpers encapsulate common patterns and best practices, reducing the amount of boilerplate code and ensuring a consistent approach to form creation.

9. How can you include JavaScript or CSS files in a Rails view?

In a Rails view, you can include JavaScript and CSS files using the javascript_include_tag and stylesheet_link_tag helper methods. These methods generate HTML tags that include the specified JavaScript or CSS files in your view.

Including JavaScript files

Inline JavaScript

To include inline JavaScript directly in your view, you can use the javascript_tag helper.

<%= javascript_tag do %>
alert('Hello, world!');
<% end %>

External JavaScript files

To include external JavaScript files, use the javascript_include_tag helper. Place this in the <head> section of your layout file (e.g., app/views/layouts/application.html.erb) to include the JavaScript file on every page.

<%= javascript_include_tag 'filename' %>

Replace 'filename' with the actual name of your JavaScript file without the extension (Rails assumes .js).

Including CSS files

Inline CSS

To include inline CSS directly in your view, you can use the stylesheet_tag helper.

<%= stylesheet_tag do %>
body { background-color: #eee; }
<% end %>

External CSS files

To include external CSS files, use the stylesheet_link_tag helper. Like with JavaScript, place this in the <head> section of your layout file to include the CSS file on every page.

<%= stylesheet_link_tag 'filename' %>

Replace 'filename' with the actual name of your CSS file without the extension (Rails assumes .css).

Combining multiple files

You can include multiple JavaScript or CSS files by providing an array of filenames to the respective helper methods. For example:

<%= javascript_include_tag 'file1', 'file2', 'file3' %>
<%= stylesheet_link_tag 'style1', 'style2', 'style3' %>

Make sure your JavaScript and CSS files are placed in the correct directories within the app/assets/javascripts and app/assets/stylesheets folders. Rails conventionally uses the asset pipeline to manage these files.

10. What is the asset pipeline in Ruby on Rails, and why is it important?

The asset pipeline is a feature in Ruby on Rails designed to manage and optimize the use of assets such as stylesheets, JavaScript files, and images in a web application. Its primary goals are to improve the efficiency of asset organization, reduce load times, and facilitate the development and deployment of web applications.

Concatenation and Minification: The asset pipeline combines multiple CSS and JavaScript files into single files, reducing the number of HTTP requests required to load a page. Additionally, it can minify these files by removing unnecessary whitespace and comments, further reducing file size and improving loading times.

Asset Compilation: The pipeline can compile higher-level languages like Sass or CoffeeScript into their respective CSS and JavaScript counterparts. This allows developers to write code in a more expressive and maintainable manner while still delivering optimized assets to the browser.

Fingerprinting: To facilitate cache control and versioning, the asset pipeline automatically appends a unique fingerprint to each asset file based on its content. This fingerprint changes when the content of the file changes, ensuring that browsers retrieve the latest version of the asset when it is updated.

Asset Organization: The conventional directory structure of the asset pipeline helps organize different types of assets. For example, stylesheets go in the app/assets/stylesheets directory, JavaScript files in app/assets/javascripts, and images in app/assets/images. This organization simplifies asset management and makes it easier for developers to locate and maintain files.

Asset Helpers: Rails provides helper methods like javascript_include_tag and stylesheet_link_tag to include assets in views. These helpers automatically generate the HTML tags needed to include the assets, considering their location and any configured pipeline transformations.

Precompilation: In production environments, Rails precompiles and compresses assets before deployment. This process prepares the application for faster delivery and minimizes the work that the server needs to do when serving assets.

Why the Asset Pipeline is Important

Performance Optimization: By reducing the number of HTTP requests, compressing files, and using fingerprinting for cache control, the asset pipeline significantly improves the performance of web applications. Faster loading times contribute to a better user experience.

Code Organization: The asset pipeline enforces a clear and organized structure for managing stylesheets, JavaScript, and images. This helps developers maintain a modular and scalable codebase.

Development Efficiency: Developers can work with higher-level languages like Sass and CoffeeScript while the asset pipeline takes care of compiling them into standard CSS and JavaScript. This allows for a more expressive and efficient development process.

Versioning and Cache Control: Fingerprinting ensures that browsers always fetch the latest version of an asset when it changes, reducing the risk of users seeing outdated or cached content.

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