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_collection_of_partials "topic", 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 = ActionController::Caching::Fragments::MemoryStore.new ActionController::Base.fragment_cache_store = ActionController::Caching::Fragments::FileStore.new("/path/to/cache/directory") ActionController::Base.fragment_cache_store = ActionController::Caching::Fragments::DRbStore.new("druby://localhost:9192") ActionController::Base.fragment_cache_store = ActionController::Caching::Fragments::FileStore.new("localhost")
Called by CacheHelper#cache
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 264 264: def cache_erb_fragment(block, name = {}, options = {}) 265: unless perform_caching then block.call; return end 266: 267: buffer = eval("_erbout", block.binding) 268: 269: if cache = read_fragment(name, options) 270: buffer.concat(cache) 271: else 272: pos = buffer.length 273: block.call 274: write_fragment(name, buffer[pos..-1], options) 275: end 276: end
Name can take one of three forms:
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 303 303: def expire_fragment(name, options = {}) 304: return unless perform_caching 305: 306: key = fragment_cache_key(name) 307: 308: if key.is_a?(Regexp) 309: fragment_cache_store.delete_matched(key, options) 310: logger.info "Expired fragments matching: #{key.source}" unless logger.nil? 311: else 312: fragment_cache_store.delete(key, options) 313: logger.info "Expired fragment: #{key}" unless logger.nil? 314: end 315: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 259 259: def fragment_cache_key(name) 260: name.is_a?(Hash) ? url_for(name).split("://").last : name 261: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 287 287: def read_fragment(name, options = {}) 288: return unless perform_caching 289: 290: key = fragment_cache_key(name) 291: if cache = fragment_cache_store.read(key, options) 292: logger.info "Fragment hit: #{key}" unless logger.nil? 293: cache 294: else 295: false 296: end 297: end
# File vendor/rails/actionpack/lib/action_controller/caching.rb, line 278 278: def write_fragment(name, content, options = {}) 279: return unless perform_caching 280: 281: key = fragment_cache_key(name) 282: fragment_cache_store.write(key, content, options) 283: logger.info "Cached fragment: #{key}" unless logger.nil? 284: content 285: end