Russian doll caching in Ruby on Rails - Mini Project: Build & Apply

Russian Doll Caching in Rails

📖 Scenario: You are building a blog application where each Post has many Comments. To improve performance, you want to use Russian doll caching to cache posts and their comments efficiently.

🎯 Goal: Build a Rails view that uses Russian doll caching to cache each post and its comments. This will speed up page loading by reusing cached fragments when posts or comments have not changed.

📋 What You'll Learn

Create a list of posts with comments in the view

Add a cache key variable for posts

Use nested cache blocks for posts and their comments

Complete the view with proper cache blocks to enable Russian doll caching

💡 Why This Matters

🌍 Real World

Russian doll caching is used in real Rails apps to speed up page rendering by caching nested data efficiently, such as blog posts with comments or product listings with reviews.

💼 Career

Understanding Russian doll caching is important for Rails developers to optimize app performance and reduce server load in production environments.

1

Set up posts and comments data in the view

In the Rails view file, create a variable called posts that contains all posts with their associated comments loaded using Post.includes(:comments).

Ruby on Rails

# Your code here
posts = Post.includes(:comments)

Need a hint?

Use Post.includes(:comments) to load posts with comments efficiently.

2

Create a cache key variable for each post

Add a variable called post_cache_key inside the loop that iterates over posts. Set it to post.cache_key to use Rails cache versioning for posts.

Ruby on Rails

posts = Post.includes(:comments)

posts.each do |post|
  # Create post_cache_key variable here
  # Your code here
end

Need a hint?

Use post.cache_key to get a cache key that changes when the post updates.

3

Add nested cache blocks for posts and comments

Inside the posts.each do |post| ... end loop, add a cache block using cache(post_cache_key). Inside that block, add another cache block for each comment using cache(comment) while iterating over post.comments.

Ruby on Rails

posts = Post.includes(:comments)

posts.each do |post|
  post_cache_key = post.cache_key
  # Add cache blocks for post and comments here
  # Your code here
end

Need a hint?

Use nested cache blocks: one for the post and one inside for each comment.

4

Complete the view with proper cache blocks

Wrap the entire posts list in a content_tag :div, id: 'posts' block. Ensure the nested cache blocks are inside this container to complete the Russian doll caching structure.

Ruby on Rails

# Wrap posts list in a div with id 'posts'
# Your code here
posts = Post.includes(:comments)

posts.each do |post|
  post_cache_key = post.cache_key
  cache(post_cache_key) do
    concat content_tag(:h2, post.title)
    post.comments.each do |comment|
      cache(comment) do
        concat content_tag(:p, comment.body)
      end
    end
  end
end

Need a hint?

Use content_tag :div, id: 'posts' do to wrap the posts list and include all cache blocks inside.