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# All subclasses of ActiveRecord::Base have one named scope:
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# * <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>
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# These anonymous \scopes tend to be useful when procedurally generating complex queries, where passing
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# intermediate values (scopes) around as first-class objects is convenient.
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# You can define a scope that applies to all finders using ActiveRecord::Base.default_scope.
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def self.included(base)
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named_scope :scoped, lambda { |scope| scope }
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read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {})
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# Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query,
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# such as <tt>:conditions => {:color => :red}, :select => 'shirts.*', :include => :washing_instructions</tt>.
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# class Shirt < ActiveRecord::Base
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# named_scope :red, :conditions => {:color => 'red'}
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# named_scope :dry_clean_only, :joins => :washing_instructions, :conditions => ['washing_instructions.dry_clean_only = ?', true]
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# The above calls to <tt>named_scope</tt> define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red,
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# in effect, represents the query <tt>Shirt.find(:all, :conditions => {:color => 'red'})</tt>.
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# Unlike <tt>Shirt.find(...)</tt>, however, the object returned by Shirt.red is not an Array; it resembles the association object
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# constructed by a <tt>has_many</tt> declaration. For instance, you can invoke <tt>Shirt.red.find(:first)</tt>, <tt>Shirt.red.count</tt>,
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# <tt>Shirt.red.find(:all, :conditions => {:size => 'small'})</tt>. Also, just
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# as with the association objects, named \scopes act like an Array, implementing Enumerable; <tt>Shirt.red.each(&block)</tt>,
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# <tt>Shirt.red.first</tt>, and <tt>Shirt.red.inject(memo, &block)</tt> all behave as if Shirt.red really was an Array.
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# 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.
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# Nested finds and calculations also work with these compositions: <tt>Shirt.red.dry_clean_only.count</tt> returns the number of garments
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# for which these criteria obtain. Similarly with <tt>Shirt.red.dry_clean_only.average(:thread_count)</tt>.
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# All \scopes are available as class methods on the ActiveRecord::Base descendant upon which the \scopes were defined. But they are also available to
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# <tt>has_many</tt> associations. If,
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# class Person < ActiveRecord::Base
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# then <tt>elton.shirts.red.dry_clean_only</tt> will return all of Elton's red, dry clean
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# Named \scopes can also be procedural:
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# class Shirt < ActiveRecord::Base
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# named_scope :colored, lambda { |color|
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# { :conditions => { :color => color } }
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# In this example, <tt>Shirt.colored('puce')</tt> finds all puce shirts.
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# Named \scopes can also have extensions, just as with <tt>has_many</tt> declarations:
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# class Shirt < ActiveRecord::Base
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# named_scope :red, :conditions => {:color => 'red'} do
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# For testing complex named \scopes, you can examine the scoping options using the
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# <tt>proxy_options</tt> method on the proxy itself.
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# class Shirt < ActiveRecord::Base
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# named_scope :colored, lambda { |color|
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# { :conditions => { :color => color } }
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# expected_options = { :conditions => { :colored => 'red' } }
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# assert_equal expected_options, Shirt.colored('red').proxy_options
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def named_scope(name, options = {}, &block)
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scopes[name] = lambda do |parent_scope, *args|
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Scope.new(parent_scope, case options
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(class << self; self end).instance_eval do
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define_method name do |*args|
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scopes[name].call(self, *args)
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attr_reader :proxy_scope, :proxy_options, :current_scoped_methods_when_defined
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NON_DELEGATE_METHODS = %w(nil? send object_id class extend find size count sum average maximum minimum paginate first last empty? any? respond_to?).to_set
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[].methods.each do |m|
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unless m =~ /^__/ || NON_DELEGATE_METHODS.include?(m.to_s)
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delegate m, :to => :proxy_found
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delegate :scopes, :with_scope, :scoped_methods, :to => :proxy_scope
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def initialize(proxy_scope, options, &block)
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[options[:extend]].flatten.each { |extension| extend extension } if options[:extend]
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extend Module.new(&block) if block_given?
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unless Scope === proxy_scope
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@current_scoped_methods_when_defined = proxy_scope.send(:current_scoped_methods)
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@proxy_scope, @proxy_options = proxy_scope, options.except(:extend)
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if args.first.kind_of?(Integer) || (@found && !args.first.kind_of?(Hash))
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proxy_found.first(*args)
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if args.first.kind_of?(Integer) || (@found && !args.first.kind_of?(Hash))
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proxy_found.last(*args)
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@found ? @found.length : count
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@found ? @found.empty? : count.zero?
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def respond_to?(method, include_private = false)
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super || @proxy_scope.respond_to?(method, include_private)
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proxy_found.any? { |*block_args| yield(*block_args) }
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def method_missing(method, *args, &block)
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if scopes.include?(method)
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scopes[method].call(self, *args)
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with_scope({:find => proxy_options, :create => proxy_options[:conditions].is_a?(Hash) ? proxy_options[:conditions] : {}}, :reverse_merge) do
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method = :new if method == :build
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if current_scoped_methods_when_defined && !scoped_methods.include?(current_scoped_methods_when_defined)
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with_scope current_scoped_methods_when_defined do
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proxy_scope.send(method, *args, &block)
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proxy_scope.send(method, *args, &block)