Rails 2.1 new features

http://www.javaeye.com/news/2320
has_one :through
class Magazine <>
  has_many :subscriptions  
end  
  
class Subscription <>
  belongs_to :magazine  
  belongs_to :user  
end  
  
class User <>
  has_many :subscriptions  
  has_one :magazine, :through => : subscriptions, :conditions => ['subscriptions.active = ?', true]  
end 



http://www.javaeye.com/news/2334
Gem: Dependencies
Rails::Initializer.run do |config|   
  
  # Require the latest version of haml  
  config.gem "haml"  
  
  # Require a specific version of chronic  
  config.gem "chronic", :version => '0.2.3'  
  
  # Require a gem from a non-standard repo  
  config.gem "hpricot", :source => "http://code.whytheluckystiff.net"  
  
  # Require a gem that needs to require a file different than the gem's name  
  # I.e. if you normally load the gem with require 'aws/s3' instead of  
  # require 'aws-s3' then you would need to specify the :lib option  
  config.gem "aws-s3", :lib => "aws/s3"   
end  


http://www.javaeye.com/news/2349
Dirty Objects
article = Article.find(:first)  
article.changed?  #=> false  
  
# Track changes to individual attributes with  
# attr_name_changed? accessor  
article.title  #=> "Title"  
article.title = "New Title"  
article.title_changed? #=> true  
  
# Access previous value with attr_name_was accessor  
article.title_was  #=> "Title"  
  
# See both previous and current value with attr_name_change accessor  
article.title_change  #=> ["Title", "New Title"] 
# Get a list of changed attributes  
article.changed  #=> ['title']  
  
# Get the hash of changed attributes and their previous and current values  
article.changes  #=> { 'title' => ["Title", "New Title"] } 
http://www.javaeye.com/news/2367
Partial updates
article = Article.find(:first)  
article.title  #=> "Title"  
article.subject  #=> "Edge Rails"  
  
# Update one of the attributes  
article.title = "New Title"  
  
# And only that updated attribute is persisted to the db  
article.save  
#=>  "UPDATE articles SET title = 'New Title' WHERE id = 1"
ActiveRecord::Base.partial_updates = true

http://www.javaeye.com/news/2377
named_scope

http://www.javaeye.com/news/2392
UTC-based Migration

http://www.javaeye.com/news/2417
http://mad.ly/2008/04/09/rails-21-time-zone-support-an-overview/
http://wiki.rubyonrails.org/rails/pages/HowtoSetDefaultTimeZone
http://blog.labratz.net/articles/2007/4/11/rails-time-zone-guide-for-beginners