系列文章汇总《Ruby on Rails 2.1新特性》

Nick Kallen的广受欢迎的has_finder插件将会被加入到Rails 2.x版本中，以named_scope方式出现。

Ruby代码

class User < ActiveRecord::Base
  named_scope :active, :conditions => {:active => true}
  named_scope :inactive, :conditions => {:active => false}
  named_scope :recent, lambda { { :conditions => ['created_at > ?', 1.week.ago] } }
end

# Standard usage
User.active    # same as User.find(:all, :conditions => {:active => true})
User.inactive # same as User.find(:all, :conditions => {:active => false})
User.recent   # same as User.find(:all, :conditions => ['created_at > ?', 1.week.ago])

# They're nest-able too!
User.active.recent
  # same as:
  # User.with_scope(:conditions => {:active => true}) do
  #   User.find(:all, :conditions => ['created_at > ?', 1.week.ago])
  # end

你所喜欢的has_finder所有优点现在都被named_scope提供——还附带一些额外的优点。User.all成了User.find(:all)的另一种写法。


高级特性：

那些对discriminating有更多需求的，别忘了还有has_finder里的一些技巧。

传递参数

在运行时，将参数传递给named scope中的特定条件。


Ruby代码

class User < ActiveRecord::Base
  named_scope :registered, lambda { |time_ago| { :conditions => ['created_at > ?', time_ago] }
end

User.registered 7.days.ago # same as User.find(:all, :conditions => ['created_at > ?', 7.days.ago])

扩展Named Scope

扩展named scipes(一种类似集合扩展的风格)

Ruby代码

class User < ActiveRecord::Base
  named_scope :inactive, :conditions => {:active => false} do
    def activate
      each { |i| i.update_attribute(:active, true) }
    end
  end
end

# Re-activate all inactive users
User.inactive.activate

匿名Scopes

你可以在第一个类使用scoped方法来传递scopes

Ruby代码

1. # Store named scopes   
2. active = User.scoped(:conditions => {:active => true})   
3. recent = User.scoped(:conditions => ['created_at > ?', 7.days.ago)   
4.   
5. # Which can be combined   
6. recent_active = recent.active   
7.   
8. # And operated upon   
9. recent_active.each { |u| ... }  

# Store named scopes
active = User.scoped(:conditions => {:active => true})
recent = User.scoped(:conditions => ['created_at > ?', 7.days.ago)

# Which can be combined
recent_active = recent.active

# And operated upon
recent_active.each { |u| ... }

name_scope是一个非常不错的功能，如果你还没开始使用它，请试着尝试下，你会发现再也离不开它了。万分感谢Nick

原文：ryandaigle.com
来自：http://www.javaeye.com/news/2377

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