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 312 312: def self.fragment_cache_store=(store_option) 313: store, *parameters = *([ store_option ].flatten) 314: @@fragment_cache_store = if store.is_a?(Symbol) 315: store_class_name = (store == :drb_store ? "DRbStore" : store.to_s.camelize) 316: store_class = ActionController::Caching::Fragments.const_get(store_class_name) 317: store_class.new(*parameters) 318: else 319: store 320: end 321: end
Called by CacheHelper#cache
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 330 330: def cache_erb_fragment(block, name = {}, options = nil) 331: unless perform_caching then block.call; return end 332: 333: buffer = eval("_erbout", block.binding) 334: 335: if cache = read_fragment(name, options) 336: buffer.concat(cache) 337: else 338: pos = buffer.length 339: block.call 340: write_fragment(name, buffer[pos..-1], options) 341: end 342: end
Name can take one of three forms:
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 367 367: def expire_fragment(name, options = nil) 368: return unless perform_caching 369: 370: key = fragment_cache_key(name) 371: 372: if key.is_a?(Regexp) 373: self.class.benchmark "Expired fragments matching: #{key.source}" do 374: fragment_cache_store.delete_matched(key, options) 375: end 376: else 377: self.class.benchmark "Expired fragment: #{key}" do 378: fragment_cache_store.delete(key, options) 379: end 380: end 381: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 325 325: def fragment_cache_key(name) 326: name.is_a?(Hash) ? url_for(name).split("://").last : name 327: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 354 354: def read_fragment(name, options = nil) 355: return unless perform_caching 356: 357: key = fragment_cache_key(name) 358: self.class.benchmark "Fragment read: #{key}" do 359: fragment_cache_store.read(key, options) 360: end 361: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 344 344: def write_fragment(name, content, options = nil) 345: return unless perform_caching 346: 347: key = fragment_cache_key(name) 348: self.class.benchmark "Cached fragment: #{key}" do 349: fragment_cache_store.write(key, content, options) 350: end 351: content 352: end