Rails 3 Sweepers

Rails 3 sweepers are same as observers but there are small changes for configuration

Create sweeper Directory

Create separate directory name ‘sweepers’ for your application in app directory

Configuration

Add your all sweepers to autooload in config/application.rb

config.autoload_paths += %W(#{config.root}/app/sweepers)

RSpec test case for sweeper

Write test cases for your sweepers

let(:photo) { FactoryGirl.create(:photo) }
    let(:sweeper) { CommentSweeper.instance}

    context "#after save" do
        it "should be called" do
            sweeper.should_receive(:after_save)
            ActiveRecord::Observer.with_observers(:comment_sweeper) do          
                photo.comments.create(:comment =>  "test")
            end         
        end     
    end

Write test case for caching

    context "#after save cache" do
        before do
            Rails.cache.clear
            ActionController::Base.perform_caching = true
            Rails.cache.write("views/photo-#{photo.id}-comments","photo comments content")
        end
        after do
            ActionController::Base.perform_caching = false
        end

        it "should be clear cached content " do         
            ActiveRecord::Observer.with_observers(:comment_sweeper) do          
                photo.comments.create(:comment =>  "update photo comments content")
            end
            Rails.cache.read("views/photo-#{photo.id}-comments").should be_nil
        end     
    end

https://github.com/patmaddox/no-peeping-toms gem required to pass this testcase

Create new sweepers and bind the model to listen

    class CommentSweeper < ActionController::Caching::Sweeper
        observe Comment # Bind to Comment model

        def after_save(comment)
            expire_cache_for(comment)
        end

        def after_destroy(comment)
            expire_cache_for(comment)
        end

        private         
            def expire_cache_for(comment)
                expire_fragment("comment-#{comment.id}")
                Rails.cache.delete("views/photo-#{comment.photo.id}-comments")                  
            end
    end

Add it to controller

class CommentsController < ApplicationController
    cache_sweeper :comment_sweeper, :only => :create

    def create
        ....
    end
end

Once comment#create executed your sweeper expires the fragment cache.

Execute your sweeper test case, it will execute without any error.