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 expire_fragment(:controller =>
"topics", :action => "list")
.
This default behavior is of limited use if you need to cache multiple
fragments per action or if the action itself is cached using
caches_action
, 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")
Removes fragments from the cache.
key
can take one of three forms:
String - This would normally take the form of a path, like
"pages/45/notes"
.
Hash - Treated as an implicit call to url_for
, like
{:controller => "pages", :action =>
"notes", :id => 45}
Regexp - Will remove any fragment that matches, so
%r{pages/\d*/notes}
might remove all notes. Make sure you
don't use anchors in the regex (^
or $
) because
the actual filename matched looks like
./cache/filename/path.cache
. 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
delete
method (or delete_matched
, for Regexp
keys.)
# File lib/action_controller/caching/fragments.rb, line 87 def expire_fragment(key, options = nil) return unless cache_configured? key = fragment_cache_key(key) unless key.is_a?(Regexp) message = nil instrument_fragment_cache :expire_fragment, key do if key.is_a?(Regexp) cache_store.delete_matched(key, options) else cache_store.delete(key, options) end end end
Given a key (as described in expire_fragment
), 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.
# File lib/action_controller/caching/fragments.rb, line 33 def fragment_cache_key(key) ActiveSupport::Cache.expand_cache_key(key.is_a?(Hash) ? url_for(key).split("://").last : key, :views) end
Check if a cached fragment from the location signified by key
exists (see expire_fragment
for acceptable formats)
# File lib/action_controller/caching/fragments.rb, line 61 def fragment_exist?(key, options = nil) return unless cache_configured? key = fragment_cache_key(key) instrument_fragment_cache :exist_fragment?, key do cache_store.exist?(key, options) end end
# File lib/action_controller/caching/fragments.rb, line 101 def instrument_fragment_cache(name, key) ActiveSupport::Notifications.instrument("#{name}.action_controller", :key => key){ yield } end
Reads a cached fragment from the location signified by key
(see expire_fragment
for acceptable formats)
# File lib/action_controller/caching/fragments.rb, line 50 def read_fragment(key, options = nil) return unless cache_configured? key = fragment_cache_key(key) instrument_fragment_cache :read_fragment, key do result = cache_store.read(key, options) result.respond_to?(:html_safe) ? result.html_safe : result end end
Writes content
to the location signified by key
(see expire_fragment
for acceptable formats)
# File lib/action_controller/caching/fragments.rb, line 38 def write_fragment(key, content, options = nil) return content unless cache_configured? key = fragment_cache_key(key) instrument_fragment_cache :write_fragment, key do content = content.html_safe.to_str if content.respond_to?(:html_safe) cache_store.write(key, content, options) end content end