Association Helper Methods with .fields for MongoMapper

gistfile1.rb

# Module to allow us to query listings and get back a Plucky object so we can
# continue to form the query before firing it off to mongo. Include this in
# any model that has many :listings. This is to get around MongoMapper 
# not allowing us to use methods on the association helper methods it adds to 
# the classes. Billy Kimble 2011-05-01

module ListingsFinder
  FIELDSETS = {
    'homepage' => ["id","title","description"]
  }
  
  def listings_finder(fieldset=nil)
    # what is our ID array? Assume the assocation is always :listings
    key = self.class.associations[:listings].options[:in]
    query = Listing.where(:_id => self.send(key))
    if fieldset && set = FIELDSETS[fieldset]
      query.fields(set)
    else
      query
    end

  end
end

class Store
	include MongoMapper::Document
	key :listing_ids, Array
	many :listings, :in => :listing_ids
	include ListingsFinder
end


@listings = Store.first.listings_finder('homepage').limit(4).all