Recenty used Rails for $work, and came up this function to make it more convenient to retrieve remote records in a many-to-many relationship with a join-table used to saved the relationship and it'll takes a .map-conversion away to get the actual records.

Here's what we came up:

module AsynapseSupport
  def has_(prefix, item)
    prefix = prefix.to_s
    item = item.to_s

    sy = "#{prefix}_#{item}"
    mo = sy.camelcase.singularize

    self.class_eval <
    has_many :_#{sy}, :class_name => "#{mo}"
    def #{sy}
      _#{sy}.map { |f| f.#{item.singularize} }
    end
EOE
  end
end

If your mixin this module in your ActiveRecord::Base, then you can say this in your user.rb model class:

  has_ :favorite, :chatrooms

It'll make an favorite_chatrooms method to retrieve a list of "Chatroom" instead of retrieving a list of "FavoriteChatroom", which is the behaviour if you say:

  has_many :favorite_chatrooms

Our has_ method, although seems to be a controversial name, is pretty handy to deal with many-to-many relationship.

Project asynapse: http://code.google.com/p/asynapse/