module ActionView # = Action View Cache Helper module Helpers module CacheHelper # This helper exposes a method for caching fragments of a view # rather than an entire action or page. This technique is useful # caching pieces like menus, lists of new topics, static HTML # fragments, and so on. This method takes a block that contains # the content you wish to cache. # # The best way to use this is by doing key-based cache expiration # on top of a cache store like Memcached that'll automatically # kick out old entries. For more on key-based expiration, see: # http://signalvnoise.com/posts/3113-how-key-based-cache-expiration-works # # When using this method, you list the cache dependency as the name of the cache, like so: # # <% cache project do %> # All the topics on this project # <%= render project.topics %> # <% end %> # # This approach will assume that when a new topic is added, you'll touch # the project. The cache key generated from this call will be something like: # # views/projects/123-20120806214154/7a1156131a6928cb0026877f8b749ac9 # ^class ^id ^updated_at ^template tree digest # # The cache is thus automatically bumped whenever the project updated_at is touched. # # If your template cache depends on multiple sources (try to avoid this to keep things simple), # you can name all these dependencies as part of an array: # # <% cache [ project, current_user ] do %> # All the topics on this project # <%= render project.topics %> # <% end %> # # This will include both records as part of the cache key and updating either of them will # expire the cache. # # ==== Template digest # # The template digest that's added to the cache key is computed by taking an md5 of the # contents of the entire template file. This ensures that your caches will automatically # expire when you change the template file. # # Note that the md5 is taken of the entire template file, not just what's within the # cache do/end call. So it's possible that changing something outside of that call will # still expire the cache. # # Additionally, the digestor will automatically look through your template file for # explicit and implicit dependencies, and include those as part of the digest. # # The digestor can be bypassed by passing skip_digest: true as an option to the cache call: # # <% cache project, skip_digest: true do %> # All the topics on this project # <%= render project.topics %> # <% end %> # # ==== Implicit dependencies # # Most template dependencies can be derived from calls to render in the template itself. # Here are some examples of render calls that Cache Digests knows how to decode: # # render partial: "comments/comment", collection: commentable.comments # render "comments/comments" # render 'comments/comments' # render('comments/comments') # # render "header" => render("comments/header") # # render(@topic) => render("topics/topic") # render(topics) => render("topics/topic") # render(message.topics) => render("topics/topic") # # It's not possible to derive all render calls like that, though. # Here are a few examples of things that can't be derived: # # render group_of_attachments # render @project.documents.where(published: true).order('created_at') # # You will have to rewrite those to the explicit form: # # render partial: 'attachments/attachment', collection: group_of_attachments # render partial: 'documents/document', collection: @project.documents.where(published: true).order('created_at') # # === Explicit dependencies # # Some times you'll have template dependencies that can't be derived at all. This is typically # the case when you have template rendering that happens in helpers. Here's an example: # # <%= render_sortable_todolists @project.todolists %> # # You'll need to use a special comment format to call those out: # # <%# Template Dependency: todolists/todolist %> # <%= render_sortable_todolists @project.todolists %> # # The pattern used to match these is /# Template Dependency: ([^ ]+)/, # so it's important that you type it out just so. # You can only declare one template dependency per line. # # === External dependencies # # If you use a helper method, for example, inside a cached block and # you then update that helper, you'll have to bump the cache as well. # It doesn't really matter how you do it, but the md5 of the template file # must change. One recommendation is to simply be explicit in a comment, like: # # <%# Helper Dependency Updated: May 6, 2012 at 6pm %> # <%= some_helper_method(person) %> # # Now all you have to do is change that timestamp when the helper method changes. # # === Automatic Collection Caching # # When rendering collections such as: # # <%= render @notifications %> # <%= render partial: 'notifications/notification', collection: @notifications %> # # If the notifications/_notification partial starts with a cache call as: # # <% cache notification do %> # <%= notification.name %> # <% end %> # # The collection can then automatically use any cached renders for that # template by reading them at once instead of one by one. # # See ActionView::Template::Handlers::ERB.resource_cache_call_pattern for # more information on what cache calls make a template eligible for this # collection caching. # # The automatic cache multi read can be turned off like so: # # <%= render @notifications, cache: false %> def cache(name = {}, options = nil, &block) if controller.respond_to?(:perform_caching) && controller.perform_caching safe_concat(fragment_for(cache_fragment_name(name, options), options, &block)) else yield end nil end # Cache fragments of a view if +condition+ is true # # <% cache_if admin?, project do %> # All the topics on this project # <%= render project.topics %> # <% end %> def cache_if(condition, name = {}, options = nil, &block) if condition cache(name, options, &block) else yield end nil end # Cache fragments of a view unless +condition+ is true # # <% cache_unless admin?, project do %> # All the topics on this project # <%= render project.topics %> # <% end %> def cache_unless(condition, name = {}, options = nil, &block) cache_if !condition, name, options, &block end # This helper returns the name of a cache key for a given fragment cache # call. By supplying skip_digest: true to cache, the digestion of cache # fragments can be manually bypassed. This is useful when cache fragments # cannot be manually expired unless you know the exact key which is the # case when using memcached. def cache_fragment_name(name = {}, options = nil) skip_digest = options && options[:skip_digest] if skip_digest name else fragment_name_with_digest(name) end end # Given a key (as described in ActionController::Caching::Fragments.expire_fragment), # returns a key suitable for use in reading, writing, or expiring a # cached fragment. 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) end private def fragment_name_with_digest(name) #:nodoc: if @virtual_path names = Array(name.is_a?(Hash) ? controller.url_for(name).split("://").last : name) digest = Digestor.digest name: @virtual_path, finder: lookup_context, dependencies: view_cache_dependencies [ *names, digest ] else name end end # TODO: Create an object that has caching read/write on it def fragment_for(name = {}, options = nil, &block) #:nodoc: read_fragment_for(name, options) || write_fragment_for(name, options, &block) end def read_fragment_for(name, options) #:nodoc: controller.read_fragment(name, options) end def write_fragment_for(name, options) #:nodoc: # VIEW TODO: Make #capture usable outside of ERB # This dance is needed because Builder can't use capture pos = output_buffer.length yield output_safe = output_buffer.html_safe? fragment = output_buffer.slice!(pos..-1) if output_safe self.output_buffer = output_buffer.class.new(output_buffer) end controller.write_fragment(name, fragment, options) end end end end