Public and assets folders in Ruby on Rails

Introduction

The public and assets folders help organize files that your Rails app sends directly to the browser, like images, styles, and scripts.

You want to add a logo image that everyone visiting your site can see.

You need to include custom CSS or JavaScript files for styling or interactivity.

You want to serve static files like robots.txt or favicon.ico.

You want to organize files that don't change often and don't need server processing.

You want to improve page load speed by serving precompiled assets.

Syntax

Ruby on Rails

app/assets/
  stylesheets/
  javascripts/
  images/
public/
  favicon.ico
  robots.txt
  other static files

The app/assets folder holds files processed by Rails before sending to the browser.

The public folder holds static files served as-is without processing.

Examples

Place CSS, JS, and images here to be compiled and served by Rails.

Ruby on Rails

app/assets/stylesheets/application.css
app/assets/javascripts/application.js
app/assets/images/logo.png

Place static files here that Rails serves directly without changes.

Ruby on Rails

public/robots.txt
public/favicon.ico
public/404.html

Sample Program

This example shows how CSS in app/assets is linked in views and how static files in public are served directly.

Ruby on Rails

# Folder structure example
# app/assets/stylesheets/custom.css
body {
  background-color: #f0f0f0;
}

# public/robots.txt
User-agent: *
Disallow:

# In a Rails view (app/views/layouts/application.html.erb):
# <%= stylesheet_link_tag 'custom', media: 'all' %>

# When you start the Rails server and visit the site:
# - The custom.css styles apply to the page.
# - The robots.txt file is accessible at /robots.txt

Important Notes

Files in app/assets are processed by Rails (like minifying CSS/JS).

Files in public are served exactly as they are, no processing.

Use app/assets for files that change often or need preprocessing.

Summary

The public folder holds static files served directly.

The assets folder holds files Rails processes before sending.

Use these folders to organize images, styles, scripts, and static files for your app.

Practice

1. What is the main purpose of the public folder in a Rails application?

easy

A. To store static files served directly without processing

B. To hold Ruby code files for controllers and models

C. To keep database migration files

D. To store files that Rails compiles before sending

Solution

1. Step 1: Understand the role of the public folder

   The public folder contains files like images, HTML, or JavaScript that Rails serves directly to the browser without any processing.

2. Step 2: Compare with other folders

   The assets folder is for files Rails processes (like compiling CSS or JavaScript), so it is not the public folder's role.

3. Final Answer:

   To store static files served directly without processing -> Option A

4. Quick Check:

   Public folder = static files served directly [OK]

Hint: Public folder serves files as-is, no processing needed [OK]

Common Mistakes:

• Confusing public with assets folder
• Thinking public holds Ruby code
• Assuming public processes files before serving

2. Which of the following is the correct path to place a CSS file that Rails will precompile and serve?

easy

A. app/public/stylesheets/style.css

B. public/assets/stylesheets/style.css

C. app/assets/stylesheets/style.css

D. config/assets/stylesheets/style.css

Solution

1. Step 1: Identify the standard assets folder for stylesheets

   Rails expects CSS files to be inside app/assets/stylesheets for precompilation and processing.

2. Step 2: Eliminate incorrect paths

   The public folder is for static files, not processed assets. The config folder does not hold assets.

3. Final Answer:

   app/assets/stylesheets/style.css -> Option C

4. Quick Check:

   CSS in assets/stylesheets = app/assets/stylesheets/style.css [OK]

Hint: Assets folder is inside app/, not public or config [OK]

Common Mistakes:

• Placing CSS directly in public folder
• Using wrong folder like config/assets
• Confusing assets with public folder paths

3. Given a file logo.png placed inside public/images, what URL path will serve this image in a Rails app?

medium

A. /assets/images/logo.png

B. /public/images/logo.png

C. /app/assets/images/logo.png

D. /images/logo.png

Solution

1. Step 1: Understand how public folder maps to URL

   Files inside public are served from the root URL path. So public/images/logo.png is accessible at /images/logo.png.

2. Step 2: Eliminate other options

   /assets/images/logo.png is for assets pipeline files, not public. /public/images/logo.png and /app/assets/images/logo.png are not valid URL paths.

3. Final Answer:

   /images/logo.png -> Option D

4. Quick Check:

   Public folder maps directly to root URL [OK]

Hint: Public folder files appear at root URL path [OK]

Common Mistakes:

• Using /assets prefix for public files
• Including 'public' in URL path
• Confusing assets and public URL paths

4. You placed a JavaScript file in app/assets/javascripts but it is not loading in your Rails app. What is a likely cause?

medium

A. You forgot to include the JavaScript pack or manifest in your layout

B. The file is missing from the public folder

C. JavaScript files must be placed in public/javascripts

D. Rails does not support JavaScript in assets folder

Solution

1. Step 1: Check how assets are loaded in Rails

   Files in app/assets/javascripts need to be referenced in your layout via a manifest or pack tag to load properly.

2. Step 2: Eliminate incorrect causes

   JavaScript files do not belong in public for processing. Rails fully supports JavaScript in assets folder.

3. Final Answer:

   You forgot to include the JavaScript pack or manifest in your layout -> Option A

4. Quick Check:

   Assets must be linked in layout to load [OK]

Hint: Always include asset manifests or packs in your layout [OK]

Common Mistakes:

• Expecting assets to load without linking in layout
• Placing JS files in wrong folders
• Thinking public folder is for processed assets

5. You want to add a favicon to your Rails app that loads instantly without asset pipeline processing. Where should you place the favicon file and how should you reference it in your HTML?

hard

A. Place in app/assets/images and use <%= favicon_link_tag 'favicon.ico' %>

B. Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'>

C. Place in app/assets/images and use <link rel='icon' href='/assets/favicon.ico'>

D. Place in public/images and use <%= image_tag 'favicon.ico' %>

Solution

1. Step 1: Choose folder for instant loading without processing

   Files in public are served directly, so placing favicon.ico in public root ensures instant loading.

2. Step 2: Reference favicon correctly in HTML

   Use a standard HTML <link> tag with href pointing to /favicon.ico for browsers to find it.

3. Final Answer:

   Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'> -> Option B

4. Quick Check:

   Favicon in public root + direct link = Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'> [OK]

Hint: Put favicon in public root and link with standard HTML tag [OK]

Common Mistakes:

• Placing favicon in assets and expecting instant load
• Using image_tag instead of link tag for favicon
• Referencing wrong URL path for favicon