module ActiveRecord
module NamedScope
# All subclasses of ActiveRecord::Base have two named_scopes:
# * <tt>all</tt>, which is similar to a <tt>find(:all)</tt> query, and
# * <tt>scoped</tt>, which allows for the creation of anonymous scopes, on the fly:
#
# Shirt.scoped(:conditions => {:color => 'red'}).scoped(:include => :washing_instructions)
#
# These anonymous scopes tend to be useful when procedurally generating complex queries, where passing
# intermediate values (scopes) around as first-class objects is convenient.
def self.included(base)
base.class_eval do
extend ClassMethods
named_scope :all
named_scope :scoped, lambda { |scope| scope }
end
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 <tt>Shirt.red</tt> and <tt>Shirt.dry_clean_only</tt>. <tt>Shirt.red</tt>,
# in effect, represents the query <tt>Shirt.find(:all, :conditions => {:color => 'red'})</tt>.
#
# Unlike Shirt.find(...), however, the object returned by <tt>Shirt.red</tt> 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, name scopes acts 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 were 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 descendent 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
#
def named_scope(name, options = {}, &block)
scopes[name] = lambda do |parent_scope, *args|
Scope.new(parent_scope, case options
when Hash
options
when Proc
options.call(*args)
end, &block)
end
(class << self; self end).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
[].methods.each { |m| delegate m, :to => :proxy_found unless m =~ /(^__|^nil\?|^send|class|extend|find|count|sum|average|maximum|minimum|paginate)/ }
delegate :scopes, :with_scope, :to => :proxy_scope
def initialize(proxy_scope, options, &block)
[options[:extend]].flatten.each { |extension| extend extension } if options[:extend]
extend Module.new(&block) if block_given?
@proxy_scope, @proxy_options = proxy_scope, options.except(:extend)
end
def reload
load_found; self
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 do
proxy_scope.send(method, *args, &block)
end
end
end
def load_found
@found = find(:all)
end
end
end
end
