In a nutshell:

• Overview       
  
• Asset Pipeline       
  
• HTTP Streaming       
  
• Identity Maps       
  
• Reversible Migrations       
  
• Upgrading to 3.1
  

Overview:

• To install rails 3.1, create a gemset using rvm.   
• Then install rails 3.1 gem as below:
• rvm gemset create rails3.1 -> rvm gemset use rails3.1 --default -> gem install rails
• Rails 3.1 includes 'jquery' as it's default javascript library.
• It also auto runs the bundler while creating a new app.   
• So inorder to create a new app, use prototype as default library and to skip auto-bundle do:
• rails new test_app -j prototype --skip-bundle
• Now open the gemfile with a text editor where you see that certain gems are included by default.
• An important addition to the gem file is the assets group which includes CoffeeScript, SASS and uglifier by default.       
• CoffeeScript is a scripting language which complies into javascript.       
• SASS is an extension of CSS which offers features like nesting and variables in styling.       
• Uglifier is a javascript minifier.       
• And also under test group 'turn' gem which makes the test output look pretty.
• Apart from these new additions, we are going to include a gem 'therubyracer' which is a javascript runtime.
• Now run 'bundle install' and take a look the directory structure.       
• The major change we see here is that a new directory 'assets' has been added under 'app' directory.       
• And the resources as such images, javascripts and stylesheets from 'public' directory has been relocated to this new directory 'assets'.

Asset Pipeline:

• The asset pipeline is one of the biggest new features in Rails 3.1.   
• Take a look at the assets directory under which we have javascripts, stylesheets and images.   
• Both the javascripts and stylesheets directory have manifest file, 'application.js' and 'application.css' respectively.   
• Each of these manifest file will be compiled into including all the files listed here.
• These manifest files are managed by sprockets, which is a ruby library for compiling and serving web assets.   
• When a request comes in, sprockets, looks at manifest and compiles every file mentioned in here.   
• By default entire directory structure of assets is included, hence any javascript or css file is compiled.   
• These assets are automatically cached and served by the Rack Cache middleware so they’re pretty fast.
• If we want to have the webserver itself handle serving and hosting the assets instead we can precompile them by running, 'rake assets:precompile'
• These manifest files eliminates the need of including the javascripts and css files explicitly.  
•  In the layout file we just need to include the manifest files and the rest is pulled out from the manifest.

HTTP Streaming:

• The ordinary http requests happens in 3 steps, http request -> dynamic content generation -> http response.   
• But in http streaming the conent is generated as chunks and each chunch is sent over while the next chunk is being generated.   
• This significantly reduces the response time.   
• On local machine under development  environment  we can use unicorn server to demonstrate this, but any improvement is too small to notice as the response is fast.
• Where as on production, there will be significant improvement over http response.       
• Currently Phusion Passenger 2.2.5 on wards support http streaming.       
• In order to start streaming all we need to do is add a small piece of  code to the controller.

Identity Map:

• Indentity maps is one of the important addtions to rails 3.1.       
• It is by default disabled in config file application.rb       
• Inorder to enable it we add,
• config.active_record.identity_map = true  and ActiveRecord::IdentityMap.enabled = true
• Now that the identity map is enabled, whenever a object is created, it is loaded into memory.       
• And during the same instance if the same object is requested, it is loaded from the memory instead of database.       
• This reduces the load time.

Reversible Migrations:

• In rails 3.1 the 'up' and 'down' methods are eliminated and a single method 'change' is introduced which performs both the functions.
• Find more info on reversible migrations here.

Upgrading to 3.1:

• Upgrading to rails 3.0.X  to 3.1.X is pretty simple.       
• First we need to update the app to latest 3.0.X version, which at this time is 3.0.10       
• Just edit the gemfile, change the version of rails and run 'bundle update'.       
• Then again edit the gemfile and include the following gems and run 'bundle update'

• Now add the following code to config/application.rb

• Go to config/environment/development.rb and comment out "config.action_view.debug_rjs = true"   
• And include "config.assets.compress = false" and "config.assets.debug = true".   
• Now go to config/environment/production.rb and include 'config.serve_static_assets = true' and 'config.static_cache_control = "public, max-age=3600" '   .
• Then go to config/environment/test.rb and include "config.assets.compress = true",  "config.assets.compile = false" and "config.assets.digest = true"
•  Add .sass-cache to to git ignore.   
• Create a directory 'assets"under 'app' directory and move the javascripts, stylesheets and image directories to this directory.   
• Edit the manifest file 'application.js' and 'application.css' as

• Include the manifest files in the layout as,

• Fire up the rails server and check whether the app is running.

Conclusion:

• This post just gives you a brief idea of the new features available in rails 3.1.
• There are a lot of resources available on the net, if you want to get into depth of rails 3.1.
• You can find the Power Point Presentation of this post here.

Cheers

Shiv

Rails Detectives