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I have been trying to use the caching capabilities of rails, but I am unable to expire some cache fragment although they seem to expire. Using the 'Russian Doll Caching' as pointed out in the rails tutorial site, I am using this configuration
<% cache "all_available_releases" do %> <% @releases.each do |release| %> <% cache(release) do %> <html code with> <%ruby code @release.name blah blah blah%> <%end%> <%end%> <%end%> I expire the outer caching in the release_controller.rb controller, where I use expire_fragment("all_available_releases") to expire the fragment. I use it in every method of the controller that updates or deletes or adds an entry.
This is the log of WEBrick, where although the expire fragment gets registered, 5 lines later the expired fragment is read and used while it shouldn't. This example is after a destroy call.
Processing by ReleasesController#destroy as HTML Parameters: {"authenticity_token"=>"***/***/********************+********=", "id"=>"2"} Release Load (0.1ms) SELECT "releases".* FROM "releases" WHERE "releases"."id" = ? LIMIT 1 [["id", "2"]] (0.1ms) begin transaction SQL (2.0ms) DELETE FROM "releases" WHERE "releases"."id" = ? [["id", 2]] (148.0ms) commit transaction Expire fragment views/all_available_releases (0.1ms) Redirected to http://127.0.0.1:3000/releases Completed 302 Found in 180ms (ActiveRecord: 150.2ms) Started GET "/releases" for 127.0.0.1 at 2013-07-03 13:09:51 +0300 Processing by ReleasesController#index as HTML Read fragment views/all_available_releases/41cb0a928326986f35f41c52bb3d8352 (0.1ms) Rendered releases/index.html.erb within layouts/application (0.6ms) Completed 200 OK in 5ms (Views: 4.0ms | ActiveRecord: 0.0ms) I even tried using Rails.cache.delete("all_available_releases") and it didn't work either.
if I delete <%cache "all_available_releases"%> (and one <%end%>) from my html.erb the caching works fine and gets expired whenever it should.
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I believe the issue is that when you cache the fragment in your view, a cache digest is being added to the cache key (views/all_available_releases/41cb0a928326986f35f41c52bb3d8352), but expire_fragment is not using the digest (views/all_available_releases).
If you add skip_digest: true to the cache call in the view it should prevent the digest from being used.
<% cache "all_available_releases", skip_digest: true do %> <% @releases.each do |release| %> <% cache(release) do %> <html code with> <%ruby code @release.name blah blah blah%> <%end%> <%end%> <%end%> Cache digests are only intended to be used with automatic cache expiration. If you need to manually expire cache keys then you can't use cache digests.
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Jbuilder don't support the skip_digest. After way to many failed approaches, I decided to share my answers here as it's highly related although not with a rails view as is the issue above.
Here's a related Q/issue where DHH essentially tells the guy that he can't expire fragment_caches explicitly. https://github.com/rails/cache_digests/issues/35 Everything isn't square so here's a way around this:
class MenuController def index json = Rails.cache.fetch('clients') do @items = Menu.all render_to_string( template: 'menu/index', locals: {items: @items}) end render json: json end end then you can explictly expire this anywhere, like in an observer
class MenuCacheObserver < ActiveRecord::Observer observe :menu, :menuitem, :menusubnavigation def after_save obj Rails.cache.delete(:clients) end end In a few cases this may make sense. On a general note, in most cases you should be using the object in the cache input, like json.cache! @my_object do wrapping the jbuilder view. That way it would invalidate when updated_at on the object changes.
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