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module ActiveRecord
module Associations
# Association proxies in Active Record are middlemen between the object that
# holds the association, known as the <tt>@owner</tt>, and the actual associated
# object, known as the <tt>@target</tt>. The kind of association any proxy is
# about is available in <tt>@reflection</tt>. That's an instance of the class
# ActiveRecord::Reflection::AssociationReflection.
#
# For example, given
#
# class Blog < ActiveRecord::Base
# has_many :posts
# end
#
# blog = Blog.first
#
# the association proxy in <tt>blog.posts</tt> has the object in +blog+ as
# <tt>@owner</tt>, the collection of its posts as <tt>@target</tt>, and
# the <tt>@reflection</tt> object represents a <tt>:has_many</tt> macro.
#
# This class has most of the basic instance methods removed, and delegates
# unknown methods to <tt>@target</tt> via <tt>method_missing</tt>. As a
# corner case, it even removes the +class+ method and that's why you get
#
# blog.posts.class # => Array
#
# though the object behind <tt>blog.posts</tt> is not an Array, but an
# ActiveRecord::Associations::HasManyAssociation.
#
# The <tt>@target</tt> object is not \loaded until needed. For example,
#
# blog.posts.count
#
# is computed directly through SQL and does not trigger by itself the
# instantiation of the actual post records.
class CollectionProxy < Relation # :nodoc:
delegate :target, :load_target, :loaded?, :to => :@association
delegate :select, :find, :first, :last,
:build, :create, :create!,
:concat, :replace, :delete_all, :destroy_all, :delete, :destroy, :uniq,
:sum, :count, :size, :length, :empty?,
:any?, :many?, :include?,
:to => :@association
def initialize(association)
@association = association
super association.klass, association.klass.arel_table
merge! association.scoped
end
alias_method :new, :build
def proxy_association
@association
end
# We don't want this object to be put on the scoping stack, because
# that could create an infinite loop where we call an @association
# method, which gets the current scope, which is this object, which
# delegates to @association, and so on.
def scoping
@association.scoped.scoping { yield }
end
def spawn
scoped
end
def scoped(options = nil)
association = @association
super.extending! do
define_method(:proxy_association) { association }
end
end
def respond_to?(name, include_private = false)
super ||
(load_target && target.respond_to?(name, include_private)) ||
proxy_association.klass.respond_to?(name, include_private)
end
def method_missing(method, *args, &block)
if target.respond_to?(method) || (!proxy_association.klass.respond_to?(method) && Class.respond_to?(method))
if load_target
if target.respond_to?(method)
target.send(method, *args, &block)
else
begin
super
rescue NoMethodError => e
raise e, e.message.sub(/ for #<.*$/, " via proxy for #{target}")
end
end
end
else
super
end
end
def ==(other)
load_target == other
end
# Forwards <tt>===</tt> explicitly to the \target because the instance method
# removal above doesn't catch it. Loads the \target if needed.
def ===(other)
other === load_target
end
def to_ary
load_target.dup
end
alias_method :to_a, :to_ary
def <<(*records)
proxy_association.concat(records) && self
end
alias_method :push, :<<
def clear
delete_all
self
end
def reload
proxy_association.reload
self
end
# Define array public methods because we know it should be invoked over
# the target, so we can have a performance improvement using those methods
# in association collections
Array.public_instance_methods.each do |m|
unless method_defined?(m)
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{m}(*args, &block)
target.public_send(:#{m}, *args, &block) if load_target
end
RUBY
end
end
end
end
end
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