actionpack-action_caching

Action caching for Action Pack (removed from core in Rails 4.0).

Installation

Add this line to your application's Gemfile:

gem 'actionpack-action_caching'

And then execute:

$ bundle

Or install it yourself as:

$ gem install actionpack-action_caching

Usage

Action caching is similar to page caching by the fact that the entire output of the response is cached, but unlike page caching, every request still goes through Action Pack. The key benefit of this is that filters run before the cache is served, which allows for authentication and other restrictions on whether someone is allowed to execute such action.

class ListsController < ApplicationController
  before_filter :authenticate, except: :public

  caches_page   :public
  caches_action :index, :show
end

In this example, the public action doesn't require authentication so it's possible to use the faster page caching. On the other hand index and show require authentication. They can still be cached, but we need action caching for them.

Action caching uses fragment caching internally and an around filter to do the job. The fragment cache is named according to the host and path of the request. A page that is accessed at http://david.example.com/lists/show/1 will result in a fragment named david.example.com/lists/show/1. This allows the cacher to differentiate between david.example.com/lists/ and jamis.example.com/lists/ -- which is a helpful way of assisting the subdomain-as-account-key pattern.

Different representations of the same resource, e.g. http://david.example.com/lists and http://david.example.com/lists.xml are treated like separate requests and so are cached separately. Keep in mind when expiring an action cache that action: 'lists' is not the same as action: 'list', format: :xml.

You can modify the default action cache path by passing a :cache_path option. This will be passed directly to ActionCachePath.new. This is handy for actions with multiple possible routes that should be cached differently. If a block is given, it is called with the current controller instance.

And you can also use :if (or :unless) to pass a proc that specifies when the action should be cached.

As of Rails 3.0, you can also pass :expires_in with a time interval (in seconds) to schedule expiration of the cached item.

You can use :on_hit, which accepts a Proc or Symbol/String to a controller method, to define a callback hook that is executed when a cache hit occurs, right before the body is rendered.

The following example depicts some of the points made above:

class ListsController < ApplicationController
  before_filter :authenticate, except: :public

  caches_page :public

  caches_action :index, if: Proc.new do
    !request.format.json?  # cache if is not a JSON request
  end

  caches_action :show, cache_path: { project: 1 },
    expires_in: 1.hour

  caches_action :feed, cache_path: Proc.new do
    if params[:user_id]
      user_list_url(params[:user_id], params[:id])
    else
      list_url(params[:id])
    end
  end

  caches_action :list, on_hit: Proc.new do
    fresh_when last_modified: params[:updated_at]
  end
end

If you pass layout: false, it will only cache your action content. That's useful when your layout has dynamic information.

Warning: If the format of the request is determined by the Accept HTTP header the Content-Type of the cached response could be wrong because no information about the MIME type is stored in the cache key. So, if you first ask for MIME type M in the Accept header, a cache entry is created, and then perform a second request to the same resource asking for a different MIME type, you'd get the content cached for M.

The :format parameter is taken into account though. The safest way to cache by MIME type is to pass the format in the route.

Contributing

1. Fork it.
2. Create your feature branch (git checkout -b my-new-feature).
3. Commit your changes (git commit -am 'Add some feature').
4. Push to the branch (git push origin my-new-feature).
5. Create a new Pull Request.

Code Status

• 
•