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require 'active_support/core_ext/array'
require 'active_support/core_ext/hash/except'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/class/attribute'

module ActiveRecord
  # = Active Record Named \Scopes
  module NamedScope
    extend ActiveSupport::Concern

    module ClassMethods
      # Returns an anonymous \scope.
      #
      # posts = Post.scoped
      # posts.size # Fires "select count(*) from posts" and returns the count
      # posts.each {|p| puts p.name } # Fires "select * from posts" and loads post objects
      #
      # fruits = Fruit.scoped
      # fruits = fruits.where(:colour => 'red') if options[:red_only]
      # fruits = fruits.limit(10) if limited?
      #
      # 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.
      def scoped(options = nil)
        if options
          scoped.apply_finder_options(options)
        else
          if current_scope
            current_scope.clone
          else
            scope = relation.clone
            scope.default_scoped = true
            scope
          end
        end
      end

      ##
      # Collects attributes from scopes that should be applied when creating
      # an AR instance for the particular class this is called on.
      def scope_attributes # :nodoc:
        if current_scope
          current_scope.scope_for_create
        else
          scope = relation.clone
          scope.default_scoped = true
          scope.scope_for_create
        end
      end

      ##
      # Are there default attributes associated with this scope?
      def scope_attributes? # :nodoc:
        current_scope || default_scopes.any?
      end

      # Adds a class method for retrieving and querying objects. A \scope represents a narrowing of a database query,
      # such as <tt>where(:color => :red).select('shirts.*').includes(:washing_instructions)</tt>.
      #
      # class Shirt < ActiveRecord::Base
      # scope :red, where(:color => 'red')
      # scope :dry_clean_only, joins(:washing_instructions).where('washing_instructions.dry_clean_only = ?', true)
      # end
      #
      # The above calls to <tt>scope</tt> define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red,
      # in effect, represents the query <tt>Shirt.where(:color => 'red')</tt>.
      #
      # Note that this is simply 'syntactic sugar' for defining an actual class method:
      #
      # class Shirt < ActiveRecord::Base
      # def self.red
      # where(:color => 'red')
      # end
      # end
      #
      # 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.first</tt>, <tt>Shirt.red.count</tt>, <tt>Shirt.red.where(: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
      # scope :colored, lambda { |color| where(:color => color) }
      # end
      #
      # In this example, <tt>Shirt.colored('puce')</tt> finds all puce shirts.
      #
      # On Ruby 1.9 you can use the 'stabby lambda' syntax:
      #
      # scope :colored, ->(color) { where(:color => color) }
      #
      # Note that scopes defined with \scope will be evaluated when they are defined, rather than
      # when they are used. For example, the following would be incorrect:
      #
      # class Post < ActiveRecord::Base
      # scope :recent, where('published_at >= ?', Time.now - 1.week)
      # end
      #
      # The example above would be 'frozen' to the <tt>Time.now</tt> value when the <tt>Post</tt>
      # class was defined, and so the resultant SQL query would always be the same. The correct
      # way to do this would be via a lambda, which will re-evaluate the scope each time
      # it is called:
      #
      # class Post < ActiveRecord::Base
      # scope :recent, lambda { where('published_at >= ?', Time.now - 1.week) }
      # end
      #
      # Named \scopes can also have extensions, just as with <tt>has_many</tt> declarations:
      #
      # class Shirt < ActiveRecord::Base
      # scope :red, where(:color => 'red') do
      # def dom_id
      # 'red_shirts'
      # end
      # end
      # end
      #
      # Scopes can also be used while creating/building a record.
      #
      # class Article < ActiveRecord::Base
      # scope :published, where(:published => true)
      # end
      #
      # Article.published.new.published # => true
      # Article.published.create.published # => true
      #
      # Class methods on your model are automatically available
      # on scopes. Assuming the following setup:
      #
      # class Article < ActiveRecord::Base
      # scope :published, where(:published => true)
      # scope :featured, where(:featured => true)
      #
      # def self.latest_article
      # order('published_at desc').first
      # end
      #
      # def self.titles
      # map(&:title)
      # end
      #
      # end
      #
      # We are able to call the methods like this:
      #
      # Article.published.featured.latest_article
      # Article.featured.titles

      def scope(name, scope_options = {})
        name = name.to_sym
        valid_scope_name?(name)
        extension = Module.new(&Proc.new) if block_given?

        scope_proc = lambda do |*args|
          options = scope_options.respond_to?(:call) ? scope_options.call(*args) : scope_options
          options = scoped.apply_finder_options(options) if options.is_a?(Hash)

          relation = scoped.merge(options)

          extension ? relation.extending(extension) : relation
        end

        singleton_class.send(:redefine_method, name, &scope_proc)
      end

    protected

      def valid_scope_name?(name)
        if respond_to?(name, true)
          logger.warn "Creating scope :#{name}. " \
                      "Overwriting existing method #{self.name}.#{name}."
        end
      end
    end
  end
end
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