Cache Digests

Notes

# cache digest talk

#
# There are 2 hard problems in computer science: caching, naming, and off-by-1 errors
#



# Gemfile
gem 'cache_digests'





#
# Models
#

class Winelist < ActiveRecord::Base
  belongs_to :seller
  has_many :product_listings, :dependent => :destroy
end

class ProductListing < ActiveRecord::Base
  belongs_to :winelist, :touch => true
end




#
# ERB
#

# <% cache([subdomain_cache_key, @winelist]) do %>
#   <% cache([subdomain_cache_key, @product_listing]) do %>
#   <% end %>
# <% end %>





#
# Conditional caching
#

def cache_if(condition, object, &block)
  if condition
    cache(object, &block)
  else
    yield
  end
end

# <%= simple_form_for(@winelist, :url => seller_winelist_url(@winelist)) do |form| %>
#   <% cache_if(@winelist.errors.blank?, [@winelist, 'edit']) do %>
#   <% end %>
# <% end %>





#
# Observers
#

# config/application
config.active_record.observers = :seller_observer, :winelist_observer

class SellerObserver < ActiveRecord::Observer
  def after_save(seller)
    if touch_winelists?(seller)
      seller.product_listings.each(&:touch)
    end
  end

private

  def touch_winelists?(seller)
    interesction = seller.changes.keys & [
      'minimum_bottles_per_order',
      'merchant_gateway',
      'winery_website_wine_page',
      'paypal_api_username',
      'paypal_api_password',
      'paypal_api_signature',
      'card_access_username',
      'card_access_password',
      'disabled',
      'show_cases_left'
    ]
    interesction.size > 0
  end
end





#
# pre-caching
#

class WinelistObserver < ActiveRecord::Observer
  def after_save(winelist)
    pre_cache_winelist(winelist)
  end

private

  def pre_cache_winelist(winelist)
    return if test_env? || development_env?

    command = curl_url(winelists(winelist))+ ' &'
    winelist.logger.info "\nsystem call #{command}\n\n"
    system command
  end

  def curl_url(url)
    "curl --insecure --head #{url} > /dev/null 2>&1"
  end

  def winelists(winelist)
    seller = winelist.seller
    options = { :host => DEFAULT_HOST, :protocol => 'https' }
    Rails.application.routes.url_helpers.winelists_url(seller.subdomain, winelist.anchor, options)
  end
end





#
# Problems
#

# 2 Winelists - 'Retail' and 'VIP'

# Currently assigned to Retail
  # [ X ] - Bob
  # [   ] - Don
  # [ X ] - Sally
  # [ reassign to VIP ]

class Winelist < ActiveRecord::Base
  has_many :memberships
end

class Membership < ActiveRecord::Base
  belongs_to :winelist, :touch => true
end



# try 1
def reassign
  winelist = Winelist.where(:name => params[:name]).first
  Membership.update_all({:winelist_id => winelist.id}, {:id => params[:membership_ids]})
end




# try 2
def reassign
  winelist = Winelist.where(:name => params[:name]).first
  Membership.where(:id => params[:membership_ids]).all.each { |m| m.update_attributes(:winelist_id => winelist.id) }
end




# try 3
def reassign
  winelists = Membership.where(:id => params[:membership_ids]).all.collect(&:winelist).uniq
  winelists.each(&:touch)

  winelist = Winelist.where(:name => params[:name]).first
  winelist.touch

  Membership.update_all({:winelist_id => winelist.id}, {:id => params[:membership_ids]})
  Membership.where(:id => params[:membership_ids]).all.each(&:touch)
end