Rails caching strategies for performance

# Fetch or compute pattern
def expensive_computation(user_id)
  Rails.cache.fetch("user/#{user_id}/stats", expires_in: 1.hour) do
    # This block only runs on cache miss
    calculate_user_statistics(user_id)
  end
end

# Write to cache
Rails.cache.write('user/123/profile', user.profile, expires_in: 30.minutes)

# Read from cache
profile = Rails.cache.read('user/123/profile')

# Delete from cache
Rails.cache.delete('user/123/profile')

# Multi-key operations
Rails.cache.read_multi('user/1', 'user/2', 'user/3')
Rails.cache.write_multi({ 'user/1' => data1, 'user/2' => data2 })

# Increment/Decrement (for counters)
Rails.cache.increment('page_views')
Rails.cache.decrement('items_in_stock')

# Conditional write
Rails.cache.fetch('key', race_condition_ttl: 5.seconds) do
  # Prevents cache stampede
  expensive_operation
end

# Cache exists check
if Rails.cache.exist?('key')
  Rails.cache.read('key')
else
  # Cache miss logic
end

class Post < ApplicationRecord
  belongs_to :user, touch: true  # Updates post's updated_at when user changes
  has_many :comments, dependent: :destroy

  # Counter cache
  has_many :comments, dependent: :destroy
  belongs_to :user, counter_cache: true  # Adds posts_count to users table

  # Cached method
  def expensive_calculation
    Rails.cache.fetch([cache_key, __method__]) do
      # Complex calculation here
      sleep(2)
      'result'
    end
  end

  # Cache key with version
  def cache_key_with_version
    "posts/#{id}-#{updated_at.to_i}/v2"
  end

  # Clear cache on update
  after_commit :clear_cache

  private

  def clear_cache
    Rails.cache.delete([cache_key, 'expensive_calculation'])
  end
end

# Query caching (automatic in Rails for same query in request)
Post.where(published: true).load  # Hits database
Post.where(published: true).load  # Returns cached result

# Disable query cache
Post.uncached do
  Post.where(published: true).load  # Always hits database
end

# Cache across requests with scopes
class Product < ApplicationRecord
  def self.featured
    Rails.cache.fetch('products/featured', expires_in: 1.hour) do
      where(featured: true).includes(:images).to_a
    end
  end
end

# ETags for HTTP caching (in controller)
class ProductsController < ApplicationController
  def show
    @product = Product.find(params[:id])

    fresh_when(@product)  # Sets ETag and Last-Modified
    # or
    if stale?(@product)
      respond_to do |format|
        format.html
        format.json { render json: @product }
      end
    end
  end
end

# config/environments/production.rb
config.cache_store = :redis_cache_store, {
  url: ENV['REDIS_URL'],
  connect_timeout: 30,
  read_timeout: 0.2,
  write_timeout: 0.2,
  reconnect_attempts: 1,
  error_handler: -> (method:, returning:, exception:) {
    Rails.logger.error("Redis cache error: #{exception.message}")
  },
  namespace: 'myapp',
  expires_in: 1.hour
}

# Use different cache stores
config.cache_store = :memory_store, { size: 64.megabytes }
config.cache_store = :file_store, Rails.root.join('tmp/cache')
config.cache_store = :mem_cache_store, 'localhost:11211'
config.cache_store = :null_store  # Disable caching

# Multiple cache stores
config.cache_store = :multi_store, :memory_store, :redis_cache_store