Caching in Rails

application_helper.rb

module ApplicationHelper
  def cache_key_for(model)
    prefix         = model.to_s.downcase.pluralize
    count          = model.count
    max_updated_at = model.maximum(:updated_at).try(:utc).try(:to_s, :number)

    "#{prefix}/all-#{count}-#{max_updated_at}"
  end
end

cache_invalidator.rb

module CacheInvalidator
  extend ActiveSupport::Concern

  included do
    after_create :invalidate_cache
    after_update :invalidate_cache
    after_destroy :invalidate_cache

    def invalidate_cache
      Rails.cache.clear
    end
  end
end

index.html.erb

<% cache(cache_key_for(Item)) do %>
  <div class="container">
    <div class="row">
      <div class="col-sm-12">
        <h1><%= @items.count %> Items</h1>
      </div>
    </div>
    <div class="row"></div>>
    <% @items.each do |item| %>
      <div class="col-sm-3">
        <% cache(item) do %>
          <h5><%= item.name %></h5>
          <%= link_to(image_tag(item.image_url), item_path(item)) %>
          <p><%= item.description %></p>
        <% end %>
      </div>
    <% end %>
  </div>
<% end %>

item.rb

class Item < ActiveRecord::Base
  # include CacheInvalidator
  # include ManyToManyAssociationsUpdater

  has_many :order_items
  has_many :orders, through: :order_items

  after_create  :update_orders
  after_update  :update_orders
  after_destroy :update_orders

  def update_orders
    orders.each do |order|
      order.updated_at = Time.now
      order.save
    end
  end
end

many_to_many_associations_updater.rb

module ManyToManyAssociationsUpdater
  extend ActiveSupport::Concern

  included do
    after_create  :update_associations
    after_update  :update_associations
    after_destroy :update_associations

    def associations
      self.class.reflect_on_all_associations(:has_many).map(&:name)
    end
    
    def update_associations
      associations.each { |association| update_association(association) }
    end
    
    def update_association(association)
      send(association).each { |record| record.update_attributes(updated_at: Time.now) }
    end
  end
end