Advanced Rails - Building Industrial-Strength Web Apps in Record Time

178 | Chapter 6: Performance

Action caching is triggered by thecaches_actionmethod. Here’s an example that
only allows a page to be viewed on Tuesdays:

class UserController < ApplicationController

before_filter :tuesday?, :only => :happy_tuesday

caches_action :happy_tuesday

def happy_tuesday

render :text => "Happy Tuesday!"

end

protected

def tuesday?

Time.now.wday == 2

end

end

Action-cached pages are expired with theexpire_actionmethod, which is again best
called from a cache sweeper. Alternatively, since action caching is implemented on
top of fragment caching, you can use theexpire_fragmentmethod to expire one or
many actions at once. You can even use a regular expression to expire all cached
instances of one action (or all actions if you like).

Fragment caching

When the preceding options fail, fragment caching can help. Fragment caching is
the most flexible, but least helpful, option. It is designed to store small fragments of
the page, but it makes no assumptions about your data. You can store HTML frag-
ments, XML, JSON, or even images in the fragment cache.

Manual access to the fragment cache uses theread_fragment,write_fragment, and
expire_fragmentmethods. This example caches barcode images as they are gener-
ated, to avoid generating them every time they are needed:

# /barcode/generate/12345

class BarcodeController < ApplicationController

def generate

text = params[:id]

# Retrieve barcode from fragment cache or generate it ourselves

bc = read_fragment("barcode/generate/#{text}") ||

write_fragment("barcode/generate/#{text}", Code39.to_jpeg(text))

# Write the response to the client

send_data bc, :type => 'image/jpeg', :disposition => 'inline'

end

end