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200 lines
8 KiB
Ruby
200 lines
8 KiB
Ruby
module ActionView
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# = Action View Cache Helper
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module Helpers
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module CacheHelper
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# This helper exposes a method for caching fragments of a view
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# rather than an entire action or page. This technique is useful
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# caching pieces like menus, lists of new topics, static HTML
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# fragments, and so on. This method takes a block that contains
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# the content you wish to cache.
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#
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# The best way to use this is by doing key-based cache expiration
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# on top of a cache store like Memcached that'll automatically
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# kick out old entries. For more on key-based expiration, see:
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# http://37signals.com/svn/posts/3113-how-key-based-cache-expiration-works
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#
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# When using this method, you list the cache dependency as the name of the cache, like so:
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#
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# <% cache project do %>
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# <b>All the topics on this project</b>
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# <%= render project.topics %>
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# <% end %>
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#
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# This approach will assume that when a new topic is added, you'll touch
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# the project. The cache key generated from this call will be something like:
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#
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# views/projects/123-20120806214154/7a1156131a6928cb0026877f8b749ac9
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# ^class ^id ^updated_at ^template tree digest
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#
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# The cache is thus automatically bumped whenever the project updated_at is touched.
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#
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# If your template cache depends on multiple sources (try to avoid this to keep things simple),
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# you can name all these dependencies as part of an array:
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#
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# <% cache [ project, current_user ] do %>
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# <b>All the topics on this project</b>
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# <%= render project.topics %>
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# <% end %>
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#
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# This will include both records as part of the cache key and updating either of them will
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# expire the cache.
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#
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# ==== Template digest
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#
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# The template digest that's added to the cache key is computed by taking an md5 of the
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# contents of the entire template file. This ensures that your caches will automatically
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# expire when you change the template file.
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#
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# Note that the md5 is taken of the entire template file, not just what's within the
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# cache do/end call. So it's possible that changing something outside of that call will
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# still expire the cache.
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#
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# Additionally, the digestor will automatically look through your template file for
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# explicit and implicit dependencies, and include those as part of the digest.
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#
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# The digestor can be bypassed by passing skip_digest: true as an option to the cache call:
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#
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# <% cache project, skip_digest: true do %>
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# <b>All the topics on this project</b>
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# <%= render project.topics %>
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# <% end %>
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#
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# ==== Implicit dependencies
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#
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# Most template dependencies can be derived from calls to render in the template itself.
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# Here are some examples of render calls that Cache Digests knows how to decode:
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#
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# render partial: "comments/comment", collection: commentable.comments
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# render "comments/comments"
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# render 'comments/comments'
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# render('comments/comments')
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#
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# render "header" => render("comments/header")
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#
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# render(@topic) => render("topics/topic")
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# render(topics) => render("topics/topic")
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# render(message.topics) => render("topics/topic")
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#
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# It's not possible to derive all render calls like that, though. Here are a few examples of things that can't be derived:
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#
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# render group_of_attachments
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# render @project.documents.where(published: true).order('created_at')
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#
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# You will have to rewrite those to the explicit form:
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#
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# render partial: 'attachments/attachment', collection: group_of_attachments
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# render partial: 'documents/document', collection: @project.documents.where(published: true).order('created_at')
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#
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# === Explicit dependencies
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#
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# Some times you'll have template dependencies that can't be derived at all. This is typically
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# the case when you have template rendering that happens in helpers. Here's an example:
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#
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# <%= render_sortable_todolists @project.todolists %>
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#
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# You'll need to use a special comment format to call those out:
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#
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# <%# Template Dependency: todolists/todolist %>
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# <%= render_sortable_todolists @project.todolists %>
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#
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# The pattern used to match these is /# Template Dependency: ([^ ]+)/, so it's important that you type it out just so.
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# You can only declare one template dependency per line.
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#
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# === External dependencies
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#
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# If you use a helper method, for example, inside of a cached block and you then update that helper,
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# 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
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# must change. One recommendation is to simply be explicit in a comment, like:
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#
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# <%# Helper Dependency Updated: May 6, 2012 at 6pm %>
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# <%= some_helper_method(person) %>
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#
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# Now all you'll have to do is change that timestamp when the helper method changes.
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def cache(name = {}, options = nil, &block)
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if controller.perform_caching
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safe_concat(fragment_for(cache_fragment_name(name, options), options, &block))
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else
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yield
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end
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nil
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end
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# Cache fragments of a view if +condition+ is true
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#
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# <%= cache_if admin?, project do %>
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# <b>All the topics on this project</b>
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# <%= render project.topics %>
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# <% end %>
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def cache_if(condition, name = {}, options = nil, &block)
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if condition
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cache(name, options, &block)
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else
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yield
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end
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nil
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end
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# Cache fragments of a view unless +condition+ is true
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#
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# <%= cache_unless admin?, project do %>
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# <b>All the topics on this project</b>
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# <%= render project.topics %>
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# <% end %>
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def cache_unless(condition, name = {}, options = nil, &block)
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cache_if !condition, name, options, &block
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end
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# This helper returns the name of a cache key for a given fragment cache
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# call. By supplying skip_digest: true to cache, the digestion of cache
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# fragments can be manually bypassed. This is useful when cache fragments
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# cannot be manually expired unless you know the exact key which is the
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# case when using memcached.
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def cache_fragment_name(name = {}, options = nil)
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skip_digest = options && options[:skip_digest]
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if skip_digest
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name
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else
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fragment_name_with_digest(name)
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end
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end
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private
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def fragment_name_with_digest(name) #:nodoc:
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if @virtual_path
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[
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*Array(name.is_a?(Hash) ? controller.url_for(name).split("://").last : name),
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Digestor.digest(@virtual_path, formats.last.to_sym, lookup_context, dependencies: view_cache_dependencies)
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]
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else
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name
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end
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end
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# TODO: Create an object that has caching read/write on it
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def fragment_for(name = {}, options = nil, &block) #:nodoc:
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read_fragment_for(name, options) || write_fragment_for(name, options, &block)
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end
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def read_fragment_for(name, options) #:nodoc:
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controller.read_fragment(name, options)
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end
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def write_fragment_for(name, options) #:nodoc:
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# VIEW TODO: Make #capture usable outside of ERB
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# This dance is needed because Builder can't use capture
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pos = output_buffer.length
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yield
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output_safe = output_buffer.html_safe?
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fragment = output_buffer.slice!(pos..-1)
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if output_safe
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self.output_buffer = output_buffer.class.new(output_buffer)
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end
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controller.write_fragment(name, fragment, options)
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end
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end
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end
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end
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