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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
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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
# intermediate values (scopes) around as first-class objects is convenient.
def self . included ( base )
base . class_eval do
extend ClassMethods
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>.
#
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# All scopes are available as class methods on the ActiveRecord::Base descendent upon which the scopes were defined. But they are also available to
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# <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 )
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name = name . to_sym
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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
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[ ] . methods . each do | m |
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unless m =~ / (^__|^nil \ ?|^send|^object_id$|class|extend|^find$|count|sum|average|maximum|minimum|paginate|first|last|empty \ ?|respond_to \ ?) /
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delegate m , :to = > :proxy_found
end
end
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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
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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 empty?
@found ? @found . empty? : count . zero?
end
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def respond_to? ( method , include_private = false )
super || @proxy_scope . respond_to? ( method , include_private )
end
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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
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end