AssociatedNamedScope
====================

Allows (re)using named scopes on child associations to define named scopes in the parent classes.

Specifically:

If you want to find all posts published in the month of November, you write a named scope published_in_month on Post.
If you want to find all users who have posts in the month of November, use AssociatedNamedScope to
write a named scope on User called has_posts_for_month that uses Post.published_in_month.

This plugin adds a new option :association to named_scope, which expects two suboptions:

:source -- the source association for the child named scope. You can specify nested associations using standard hash syntax (e.g., {:user=>:addresses} for the addresses of the user of the current model).
:scope -- the named scope itself. You can specify arguments to the scope by using an array [:scope_name, arg1, ...]

These scopes chain and in every way behave just like normal named_scopes. 

Examples
========

A simple example to find all users who have posts published in a given month:

class Post < ActiveRecord::Base
  belongs_to :user
  named_scope :published_in_month, lambda{|month| {:conditions=>["month(posts.publication_date)=?", month]}}
end

class User < ActiveRecord::Base
  has_many :posts
  named_scope :has_posts_for_month, lambda{|month|
    {:association=>{:source=>:posts, :scope=>[:published_in_month, month]}}
  }
end


A more complex example, using a nested association, to find all posts written by users within range of a particular address:

class Address < ActiveRecord::Base
  belongs_to :addressable, :polymorphic => true
  
  named_scope :in_range, lambda {|lat, lng, zip_code| 
    {:conditions => 
    "(
      (POW(addresses.radius,2) >= 
        (POW(69.1*(#{lat}-addresses.lat),2) + 
          POW(69.1*(#{lng}-addresses.lng) * cos(#{lat} / 57.3), 2)
        )
      )
      OR (addresses.zip = '#{zip_code}')
     )"
  }}
end

class User < ActiveRecord::Base
  has_many :posts
  has_many :addresses, :as => :addressable
end

class Post < ActiveRecord::Base
  belongs_to :user
  named_scope :within_range, lambda{|address|
    {:association=>{:source=>{:user=>:addresses}, :scope=>[:in_range, address.lat, address.lng, address.zip]}}
  }
end


Copyright (c) 2009 Monica McArthur (mechaferret@gmail.com), released under the MIT license