caching-patterns

Caching Patterns

Philosophy: Cache Aggressively, Invalidate Precisely

• HTTP caching with ETags and fresh_when for free 304 Not Modified responses
• Russian doll caching with touch: true for automatic cache invalidation
• Fragment caching in views with cache keys based on updated_at timestamps
• Solid Cache (database-backed, no Redis) for production caching
• Collection caching with cache_collection for lists
• Low-level caching with Rails.cache.fetch for expensive computations

Project Knowledge

Stack: Solid Cache (database-backed), Turbo for page refreshes, ETags with conditional GET, fragment caching in ERB views, collection caching for lists.

Multi-tenancy: Cache keys scoped to account. URL-based: app.myapp.com/123/projects/456.

Commands:

rails solid_cache:install        # Install Solid Cache
rails db:migrate                 # Run cache migrations
rails cache:clear                # Clear cache

Caching Strategy Hierarchy

Apply caching in this order (highest impact first):

1. HTTP caching -- fresh_when / stale? in controllers (free 304s)
2. Fragment caching -- cache blocks in views (Russian doll)
3. Collection caching -- cache_collection for lists of partials
4. Low-level caching -- Rails.cache.fetch for expensive computations

Pattern 1: HTTP Caching with ETags

See @references/http-caching.md for full details.

# Single resource -- returns 304 if ETag matches
class BoardsController < ApplicationController
  def show
    @board = Current.account.boards.find(params[:id])
    fresh_when @board
  end

  def index
    @boards = Current.account.boards.includes(:creator)
    fresh_when @boards
  end
end

# Composite ETag from multiple objects
def show
  fresh_when [@board, @card, Current.user]
end

# API with stale? for conditional rendering
def show
  @board = Current.account.boards.find(params[:id])
  if stale?(@board)
    render json: @board
  end
end

# Custom ETag with parameters
fresh_when etag: [@activities, @report_date, Current.user.timezone]