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{% highlight ruby %} def rebuild_site(relative) puts ">>> Change Detected to: #{relative} <<<" IO.popen('rake generate') do |io| print(io.readpartial(512)) until io.eof? end puts '>>> Update Complete <<<' end {% endhighlight %}

So that's a small example. What about a big one?

{% highlight ruby %} require 'active_support/core_ext/array' require 'active_support/core_ext/hash/except' require 'active_support/core_ext/object/metaclass'

module ActiveRecord module NamedScope extend ActiveSupport::Concern

# All subclasses of ActiveRecord::Base have one named scope:
# * <tt>scoped</tt> - which allows for the creation of anonymous \scopes, on the fly: <tt>Shirt.scoped(:conditions => {:color => 'red'}).scoped(:include => :washing_instructions)</tt>
#
# These anonymous \scopes tend to be useful when procedurally generating complex queries, where passing
# intermediate values (scopes) around as first-class objects is convenient.
#
# You can define a scope that applies to all finders using ActiveRecord::Base.default_scope.
included do
  named_scope :scoped, lambda { |scope| scope }
end

module ClassMethods
  def scopes
    read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {})
  end

  # Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query,
  # such as <tt>:conditions => {:color => :red}, :select => 'shirts.*', :include => :washing_instructions</tt>.
  #
  #   class Shirt < ActiveRecord::Base
  #     named_scope :red, :conditions => {:color => 'red'}
  #     named_scope :dry_clean_only, :joins => :washing_instructions, :conditions => ['washing_instructions.dry_clean_only = ?', true]
  #   end
  # 
  # The above calls to <tt>named_scope</tt> define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red, 
  # in effect, represents the query <tt>Shirt.find(:all, :conditions => {:color => 'red'})</tt>.
  #
  # Unlike <tt>Shirt.find(...)</tt>, however, the object returned by Shirt.red is not an Array; it resembles the association object
  # constructed by a <tt>has_many</tt> declaration. For instance, you can invoke <tt>Shirt.red.find(:first)</tt>, <tt>Shirt.red.count</tt>,
  # <tt>Shirt.red.find(:all, :conditions => {:size => 'small'})</tt>. Also, just
  # as with the association objects, named \scopes act like an Array, implementing Enumerable; <tt>Shirt.red.each(&block)</tt>,
  # <tt>Shirt.red.first</tt>, and <tt>Shirt.red.inject(memo, &block)</tt> all behave as if Shirt.red really was an Array.
  #
  # These named \scopes are composable. For instance, <tt>Shirt.red.dry_clean_only</tt> will produce all shirts that are both red and dry clean only.
  # Nested finds and calculations also work with these compositions: <tt>Shirt.red.dry_clean_only.count</tt> returns the number of garments
  # for which these criteria obtain. Similarly with <tt>Shirt.red.dry_clean_only.average(:thread_count)</tt>.
  #
  # All \scopes are available as class methods on the ActiveRecord::Base descendant upon which the \scopes were defined. But they are also available to
  # <tt>has_many</tt> associations. If,
  #
  #   class Person < ActiveRecord::Base
  #     has_many :shirts
  #   end
  #
  # then <tt>elton.shirts.red.dry_clean_only</tt> will return all of Elton's red, dry clean
  # only shirts.
  #
  # Named \scopes can also be procedural:
  #
  #   class Shirt < ActiveRecord::Base
  #     named_scope :colored, lambda { |color|
  #       { :conditions => { :color => color } }
  #     }
  #   end
  #
  # In this example, <tt>Shirt.colored('puce')</tt> finds all puce shirts.
  #
  # Named \scopes can also have extensions, just as with <tt>has_many</tt> declarations:
  #
  #   class Shirt < ActiveRecord::Base
  #     named_scope :red, :conditions => {:color => 'red'} do
  #       def dom_id
  #         'red_shirts'
  #       end
  #     end
  #   end
  #
  #
  # For testing complex named \scopes, you can examine the scoping options using the
  # <tt>proxy_options</tt> method on the proxy itself.
  #
  #   class Shirt < ActiveRecord::Base
  #     named_scope :colored, lambda { |color|
  #       { :conditions => { :color => color } }
  #     }
  #   end
  #
  #   expected_options = { :conditions => { :colored => 'red' } }
  #   assert_equal expected_options, Shirt.colored('red').proxy_options
  def named_scope(name, options = {}, &block)
    name = name.to_sym
    scopes[name] = lambda do |parent_scope, *args|
      Scope.new(parent_scope, case options
        when Hash
          options
        when Proc
          options.call(*args)
      end, &block)
    end
    metaclass.instance_eval do
      define_method name do |*args|
        scopes[name].call(self, *args)
      end
    end
  end
end

class Scope
  attr_reader :proxy_scope, :proxy_options, :current_scoped_methods_when_defined
  NON_DELEGATE_METHODS = %w(nil? send object_id class extend find size count sum average maximum minimum paginate first last empty? any? many? respond_to?).to_set
  [].methods.each do |m|
    unless m =~ /^__/ || NON_DELEGATE_METHODS.include?(m.to_s)
      delegate m, :to => :proxy_found
    end
  end

  delegate :scopes, :with_scope, :scoped_methods, :to => :proxy_scope

  def initialize(proxy_scope, options, &block)
    options ||= {}
    [options[:extend]].flatten.each { |extension| extend extension } if options[:extend]
    extend Module.new(&block) if block_given?
    unless Scope === proxy_scope
      @current_scoped_methods_when_defined = proxy_scope.send(:current_scoped_methods)
    end
    @proxy_scope, @proxy_options = proxy_scope, options.except(:extend)
  end

  def reload
    load_found; self
  end

  def first(*args)
    if args.first.kind_of?(Integer) || (@found && !args.first.kind_of?(Hash))
      proxy_found.first(*args)
    else
      find(:first, *args)
    end
  end

  def last(*args)
    if args.first.kind_of?(Integer) || (@found && !args.first.kind_of?(Hash))
      proxy_found.last(*args)
    else
      find(:last, *args)
    end
  end

  def size
    @found ? @found.length : count
  end

  def empty?
    @found ? @found.empty? : count.zero?
  end

  def respond_to?(method, include_private = false)
    super || @proxy_scope.respond_to?(method, include_private)
  end

  def any?
    if block_given?
      proxy_found.any? { |*block_args| yield(*block_args) }
    else
      !empty?
    end
  end

  # Returns true if the named scope has more than 1 matching record.
  def many?
    if block_given?
      proxy_found.many? { |*block_args| yield(*block_args) }
    else
      size > 1
    end
  end

  protected
  def proxy_found
    @found || load_found
  end

  private
  def method_missing(method, *args, &block)
    if scopes.include?(method)
      scopes[method].call(self, *args)
    else
      with_scope({:find => proxy_options, :create => proxy_options[:conditions].is_a?(Hash) ?  proxy_options[:conditions] : {}}, :reverse_merge) do
        method = :new if method == :build
        if current_scoped_methods_when_defined && !scoped_methods.include?(current_scoped_methods_when_defined)
          with_scope current_scoped_methods_when_defined do
            proxy_scope.send(method, *args, &block)
          end
        else
          proxy_scope.send(method, *args, &block)
        end
      end
    end
  end

  def load_found
    @found = find(:all)
  end
end

end end {% endhighlight %}

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