Difference b/w Rails 2 and Rails 3

Now a days Rails 3.2 version is going on. I am going to write some difference between in Rails 2.x and 3.x.

1. Some command line syntax has been changed in Rails 3.x like as

•  rails generate instead of rails script/generate
•  rails server instead of ruby server

 2. Introduction of bundler (New way to manage your gem dependencies)

       - Rails 3.x has bundle concept (Gem File) while Rails 2.x does not have

3. Gemfile and Gemfile.lock (Where all your gem dependencies lies, instead of environment.rb)

4. A new .rb file in config/ folder, named as application.rb (Which has everything that previously environment.rb had)

5. Change in SQL Structure: Model.where(:activated => true)

6. All the mailer script will now be in app/mailers folder, earlier we kept inside app/models.

7. Rails3-UJS support. for links and forms to work as AJAX, instead of writing complex lines of code, we write
:remote => true

8. HTML 5 support.

9. Changes in the model based validation syntax:
    validates :name, :presence => true

10. Ability to install windows/ruby/jruby/development/production specific gems to Gemfile.
     

    group :production do
      gem 'will_paginate'
    end 

11. Rails 3.x has changed routing syntax eg :

• Rails 2.x : map.connect ‘hello_word’, :controller=> ‘posts’, :action => ‘index’
  Rails 3.x : match “hello_world” => ‘post#index’

• Rails 2.x: map.resources  :users
  Rails 3.x:            resources  :users

• Rails 2.x : map.root   :controller => ‘posts’, :action => ‘index’
  Rails3.x:   root :to => ‘post#index’