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module ActionController #:nodoc:
module Caching
# Fragment caching is used for caching various blocks within templates without caching the entire action as a whole. This is useful when
# certain elements of an action change frequently or depend on complicated state while other parts rarely change or can be shared amongst multiple
# parties. The caching is done using the cache helper available in the Action View. A template with caching might look something like:
# <b>Hello <%= @name %></b>
# <% cache do %>
# All the topics in the system:
# <%= render :partial => "topic", :collection => Topic.find(:all) %>
# <% end %>
# This cache will bind to the name of the action that called it, so if this code was part of the view for the topics/list action, you would
# be able to invalidate it using <tt>expire_fragment(:controller => "topics", :action => "list")</tt>.
# This default behavior is of limited use if you need to cache multiple fragments per action or if the action itself is cached using
# <tt>caches_action</tt>, so we also have the option to qualify the name of the cached fragment with something like:
# <% cache(:action => "list", :action_suffix => "all_topics") do %>
# That would result in a name such as "/topics/list/all_topics", avoiding conflicts with the action cache and with any fragments that use a
# different suffix. Note that the URL doesn't have to really exist or be callable - the url_for system is just used to generate unique
# cache names that we can refer to when we need to expire the cache.
# The expiration call for this example is:
# expire_fragment(:controller => "topics", :action => "list", :action_suffix => "all_topics")
module Fragments
# Given a key (as described in <tt>expire_fragment</tt>), returns a key suitable for use in reading,
# writing, or expiring a cached fragment. If the key is a hash, the generated key is the return
# value of url_for on that hash (without the protocol). All keys are prefixed with "views/" and uses
# ActiveSupport::Cache.expand_cache_key for the expansion.
def fragment_cache_key(key)
ActiveSupport::Cache.expand_cache_key(key.is_a?(Hash) ? url_for(key).split("://").last : key, :views)
def fragment_for(buffer, name = {}, options = nil, &block) #:nodoc:
if perform_caching
if cache = read_fragment(name, options)
pos = buffer.length
write_fragment(name, buffer[pos..-1], options)
# Writes <tt>content</tt> to the location signified by <tt>key</tt> (see <tt>expire_fragment</tt> for acceptable formats)
def write_fragment(key, content, options = nil)
return content unless cache_configured?
self.class.benchmark "Cached fragment miss: #{key}" do
key = fragment_cache_key(key)
content = content.html_safe.to_str if content.respond_to?(:html_safe)
cache_store.write(key, content, options)
# Reads a cached fragment from the location signified by <tt>key</tt> (see <tt>expire_fragment</tt> for acceptable formats)
def read_fragment(key, options = nil)
return unless cache_configured?
key = fragment_cache_key(key)
self.class.benchmark "Cached fragment hit: #{key}" do
result =, options)
result.respond_to?(:html_safe) ? result.html_safe : result
# Check if a cached fragment from the location signified by <tt>key</tt> exists (see <tt>expire_fragment</tt> for acceptable formats)
def fragment_exist?(key, options = nil)
return unless cache_configured?
key = fragment_cache_key(key)
self.class.benchmark "Cached fragment exists?: #{key}" do
cache_store.exist?(key, options)
# Removes fragments from the cache.
# +key+ can take one of three forms:
# * String - This would normally take the form of a path, like
# <tt>"pages/45/notes"</tt>.
# * Hash - Treated as an implicit call to +url_for+, like
# <tt>{:controller => "pages", :action => "notes", :id => 45}</tt>
# * Regexp - Will remove any fragment that matches, so
# <tt>%r{pages/\d*/notes}</tt> might remove all notes. Make sure you
# don't use anchors in the regex (<tt>^</tt> or <tt>$</tt>) because
# the actual filename matched looks like
# <tt>./cache/filename/path.cache</tt>. Note: Regexp expiration is
# only supported on caches that can iterate over all keys (unlike
# memcached).
# +options+ is passed through to the cache store's <tt>delete</tt>
# method (or <tt>delete_matched</tt>, for Regexp keys.)
def expire_fragment(key, options = nil)
return unless cache_configured?
key = key.is_a?(Regexp) ? key : fragment_cache_key(key)
if key.is_a?(Regexp)
self.class.benchmark "Expired fragments matching: #{key.source}" do
cache_store.delete_matched(key, options)
self.class.benchmark "Expired fragment: #{key}" do
cache_store.delete(key, options)
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