rails-caching

name	rails-caching
description	Rails caching strategies including fragment caching, low-level caching with Rails.cache, cache keys, and conditional GET. Use when the user asks about caching performance or invalidation in Rails.
version	1.0.0

Rails Caching

Use Rails caching to reduce response time and database load while keeping content fresh. This skill focuses on fragment caching, low-level caching, cache keys, and conditional GETs.

Fragment caching

Wrap view fragments that can be reused:

<% @products.each do |product| %>
  <% cache product do %>
    <%= render product %>
  <% end %>
<% end %>

Notes:

• Cache keys include a template digest; edits to the fragment invalidate it.
• Model versions (cache_key_with_version) help expire cached content when records change.

Low-level caching with Rails.cache

Use Rails.cache.fetch for expensive computations:

class Product < ApplicationRecord
  def competing_price
    Rails.cache.fetch("#{cache_key_with_version}/competing_price", expires_in: 12.hours) do
      Competitor::API.find_price(id)
    end
  end
end

Guidance:

• Prefer fetch to avoid separate read/write logic.
• Choose stable keys; use arrays/hashes when appropriate.
• Set expires_in for data that should age out.

Cache keys

Objects should implement cache_key (Active Record provides it). Keys can be arrays or hashes:

Rails.cache.read(site: "mysite", owners: [owner_1, owner_2])

Notes:

• Storage backends may modify keys; don’t depend on backend-specific formats.

Conditional GETs

Leverage ETags and Last-Modified to return 304 Not Modified:

class ProductsController < ApplicationController
  def show
    @product = Product.find(params[:id])
    if stale?(last_modified: @product.updated_at.utc, etag: @product.cache_key_with_version)
      # normal response rendering
    end
  end
end

When to use this skill

• Cache expensive views or queries
• Decide between fragment and low-level caching
• Configure cache stores as needed
• Implement cache keys and conditional GETs