Module | ActionController::Caching::Fragments |
In: |
vendor/rails/actionpack/lib/action_controller/caching.rb
|
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 doing 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 action that called it. So you would be able to invalidate it using expire_fragment(:controller => "topics", :action => "list") — if that was the controller/action used. This is not too helpful if you need to cache multiple fragments per action or if the action itself is cached using caches_action. So instead we should qualify the name of the action used with something like:
<% cache(:action => "list", :action_suffix => "all_topics") do %>
That would result in a name such as "/topics/list/all_topics", which wouldn‘t conflict with any action cache and neither with another fragment using a different suffix. Note that the URL doesn‘t have to really exist or be callable. We‘re just using the url_for system to generate unique cache names that we can refer to later for expirations. The expiration call for this example would be expire_fragment(:controller => "topics", :action => "list", :action_suffix => "all_topics").
In order to use the fragment caching, you need to designate where the caches should be stored. This is done by assigning a fragment store of which there are four different kinds:
Configuration examples (MemoryStore is the default):
ActionController::Base.fragment_cache_store = :memory_store ActionController::Base.fragment_cache_store = :file_store, "/path/to/cache/directory" ActionController::Base.fragment_cache_store = :drb_store, "druby://localhost:9192" ActionController::Base.fragment_cache_store = :mem_cache_store, "localhost" ActionController::Base.fragment_cache_store = MyOwnStore.new("parameter")
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 313 313: def self.fragment_cache_store=(store_option) 314: store, *parameters = *([ store_option ].flatten) 315: @@fragment_cache_store = if store.is_a?(Symbol) 316: store_class_name = (store == :drb_store ? "DRbStore" : store.to_s.camelize) 317: store_class = ActionController::Caching::Fragments.const_get(store_class_name) 318: store_class.new(*parameters) 319: else 320: store 321: end 322: end
Called by CacheHelper#cache
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 331 331: def cache_erb_fragment(block, name = {}, options = nil) 332: unless perform_caching then block.call; return end 333: 334: buffer = eval("_erbout", block.binding) 335: 336: if cache = read_fragment(name, options) 337: buffer.concat(cache) 338: else 339: pos = buffer.length 340: block.call 341: write_fragment(name, buffer[pos..-1], options) 342: end 343: end
Name can take one of three forms:
%r{pages/\d*/notes}
Ensure you do not specify start and finish in the regex (^$) because the actual filename matched looks like ./cache/filename/path.cache Regexp expiration is not supported on caches which can‘t iterate over all keys, such as memcached.
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 373 373: def expire_fragment(name, options = nil) 374: return unless perform_caching 375: 376: key = fragment_cache_key(name) 377: 378: if key.is_a?(Regexp) 379: self.class.benchmark "Expired fragments matching: #{key.source}" do 380: fragment_cache_store.delete_matched(key, options) 381: end 382: else 383: self.class.benchmark "Expired fragment: #{key}" do 384: fragment_cache_store.delete(key, options) 385: end 386: end 387: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 326 326: def fragment_cache_key(name) 327: name.is_a?(Hash) ? url_for(name).split("://").last : name 328: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 355 355: def read_fragment(name, options = nil) 356: return unless perform_caching 357: 358: key = fragment_cache_key(name) 359: self.class.benchmark "Fragment read: #{key}" do 360: fragment_cache_store.read(key, options) 361: end 362: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 345 345: def write_fragment(name, content, options = nil) 346: return unless perform_caching 347: 348: key = fragment_cache_key(name) 349: self.class.benchmark "Cached fragment: #{key}" do 350: fragment_cache_store.write(key, content, options) 351: end 352: content 353: end