Fragment caching is used for caching various blocks within views 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 done using the cache helper available in the Action View. See ActionView::Helpers::CacheHelper for more information.

While it's strongly recommended that you use key-based cache expiration (see links in CacheHelper for more information), it is also possible to manually expire caches. For example:

expire_fragment('name_of_cache')

Namespace

Module

Methods

Instance Public methods

combined_fragment_cache_key(key)

Given a key (as described in expire_fragment), returns a key array suitable for use in reading, writing, or expiring a cached fragment. All keys begin with :views, followed by ENV or ENV if set, followed by any controller-wide key prefix values, ending with the specified key value.

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 88
      def combined_fragment_cache_key(key)
        head = self.class.fragment_cache_keys.map { |k| instance_exec(&k) }
        tail = key.is_a?(Hash) ? url_for(key).split("://").last : key
        [ :views, (ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]), *head, *tail ].compact
      end
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expire_fragment(key, options = nil)

Removes fragments from the cache.

key can take one of three forms:

  • String - This would normally take the form of a path, like pages/45/notes.

  • Hash - Treated as an implicit call to url_for, like { controller: 'pages', action: 'notes', id: 45}

  • Regexp - Will remove any fragment that matches, so %r{pages/\d*/notes} might remove all notes. Make sure you don't use anchors in the regex (^ or $) because the actual filename matched looks like ./cache/filename/path.cache. Note: Regexp expiration is only supported on caches that can iterate over all keys (unlike memcached).

options is passed through to the cache store's delete method (or delete_matched, for Regexp keys).

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 148
      def expire_fragment(key, options = nil)
        return unless cache_configured?
        key = combined_fragment_cache_key(key) unless key.is_a?(Regexp)

        instrument_fragment_cache :expire_fragment, key do
          if key.is_a?(Regexp)
            cache_store.delete_matched(key, options)
          else
            cache_store.delete(key, options)
          end
        end
      end
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fragment_cache_key(key)

Given a key (as described in expire_fragment), returns a key suitable for use in reading, writing, or expiring a cached fragment. All keys begin with views/, followed by any controller-wide key prefix values, ending with the specified key value. The key is expanded using ActiveSupport::Cache.expand_cache_key.

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 69
      def fragment_cache_key(key)
        ActiveSupport::Deprecation.warn(<<-MSG.squish)
          Calling fragment_cache_key directly is deprecated and will be removed in Rails 6.0.
          All fragment accessors now use the combined_fragment_cache_key method that retains the key as an array,
          such that the caching stores can interrogate the parts for cache versions used in
          recyclable cache keys.
        MSG

        head = self.class.fragment_cache_keys.map { |k| instance_exec(&k) }
        tail = key.is_a?(Hash) ? url_for(key).split("://").last : key
        ActiveSupport::Cache.expand_cache_key([*head, *tail], :views)
      end
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fragment_exist?(key, options = nil)

Check if a cached fragment from the location signified by key exists (see expire_fragment for acceptable formats).

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 121
      def fragment_exist?(key, options = nil)
        return unless cache_configured?
        key = combined_fragment_cache_key(key)

        instrument_fragment_cache :exist_fragment?, key do
          cache_store.exist?(key, options)
        end
      end
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read_fragment(key, options = nil)

Reads a cached fragment from the location signified by key (see expire_fragment for acceptable formats).

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 109
      def read_fragment(key, options = nil)
        return unless cache_configured?

        key = combined_fragment_cache_key(key)
        instrument_fragment_cache :read_fragment, key do
          result = cache_store.read(key, options)
          result.respond_to?(:html_safe) ? result.html_safe : result
        end
      end
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write_fragment(key, content, options = nil)

Writes content to the location signified by key (see expire_fragment for acceptable formats).

📝 Source code 
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 96
      def write_fragment(key, content, options = nil)
        return content unless cache_configured?

        key = combined_fragment_cache_key(key)
        instrument_fragment_cache :write_fragment, key do
          content = content.to_str
          cache_store.write(key, content, options)
        end
        content
      end
🔎 See on GitHub