Cache In Rails

Table of contents

Page Caching

Cache entire responses for endpoints with static content. It’s simple but powerful when the data doesn’t change often.

# config/environments/production.rb
config.action_controller.perform_caching = true
config.action_controller.page_cache_directory = "#{Rails.root.to_s}/public/deploy"

Action Caching

Cache responses while still running essential filters like authentication. This is great for authenticated APIs that return data frequently.

class ProductsController < ApplicationController
  before_action :authenticate_user!

  caches_action :index, cache_path: Proc.new { |c| c.params }

  def index
    @products = Product.all
    render json: @products
  end
end

Fragment Caching

Cache specific parts of the response, such as product details that don’t change often, while allowing other parts, like user data, to remain dynamic.

class ProductsController < ApplicationController
  def show
    @product = Product.find(params[:id])
    @user = current_user

    render json: {
      product: Rails.cache.fetch(
        "product/#{@product.id}"
      ) { @product.as_json },
      user: @user.as_json
    }
  end
end

Cache Expiration

Ensure your API serves fresh data by expiring caches when the underlying data changes. For example, invalidate the product cache when a product is updated.

class ProductsController < ApplicationController
  def update
    @product = Product.find(params[:id])
    if @product.update(product_params)
      Rails.cache.delete("product/#{@product.id}")
      render json: @product
    else
      render json: @product.errors, status: :unprocessable_entity
    end
  end
end

Redis Store

For more robust caching, especially in production environments, consider using Redis or Memcached.

# config/environments/production.rb
config.cache_store = :redis_cache_store, { url: ENV['REDIS_URL'] }

# Example usage in a controller
Rails.cache.fetch("product/#{product.id}", expires_in: 12.hours) do
  product.to_json
end

In-Memory Store

Location: The cache is stored in the server’s memory (RAM)

Use case: This is the default in development environments because it’s simple and fast but not persistent and will be cleared when the server restarts.

# config/environments/development.rb
config.cache_store = :memory_store

File Store

Location: The cache is stored as files on the disk, typically in your Rails application’s tmp/cache directory.

Use case: Useful for small-scale applications or for a simple, persistent caching mechanism.

# config/environments/development.rb
config.cache_store = :file_store, "#{Rails.root.to_s}/tmp/cache/"

Monitor & Debug

Keep an eye on cache hits and misses in your logs to fine-tune your strategy.

# config/environments/production.rb
config.log_tags = [:cache]