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')
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).
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 124 def expire_fragment(key, options = nil) return unless cache_configured? key = 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
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.
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 64 def 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 ActiveSupport::Cache.expand_cache_key([*head, *tail], :views) end
Check if a cached fragment from the location signified by key
exists (see expire_fragment
for acceptable formats).
Reads a cached fragment from the location signified by key
(see expire_fragment
for acceptable formats).
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 85 def read_fragment(key, options = nil) return unless cache_configured? key = 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
Writes content
to the location signified by key
(see expire_fragment
for acceptable formats).
# File actionpack/lib/abstract_controller/caching/fragments.rb, line 72 def write_fragment(key, content, options = nil) return content unless cache_configured? key = fragment_cache_key(key) instrument_fragment_cache :write_fragment, key do content = content.to_str cache_store.write(key, content, options) end content end