Anonymous extension modules for all associations

has_one and belongs_to associations support the :extend option (although it isn't documented) but do not support anonymous modules as easily as has_many associations.

For the sake of completeness this patch allows anonymous modules for has_one, has_one :through and belongs_to associations, so you can do things like this:

belongs_to :author do
  def greeting
    "hello"
  end
end

has_one :last_comment, :class_name => 'Comment', :order => 'id desc' do
  def what_are_you
    "the last comment associated with a post..."
  end
end

It also adds the missing :extend option to the documentation.

Without the patch you are left to do something much uglier like this:

module MyBelongsToExtension
  def greeting
    "hello"
  end
end

class Post < ActiveRecord::Base
  belongs_to :author, :extend => MyBelongsToExtension
end

or this

class Post < ActiveRecord::Base
  belongs_to :author, :extend => ( Module.new do
    def greeting
      "hello"
    end
  end )
end

Neither of which are particularly nice :)

I should also give credit to Jonathan Viney for his original belongs_to patch from just over 2 years ago