MongoMapper to give EmbeddedDocument a "delete" method

embedded_document_delete.rb

# MongoMapper "embedded document delete" plugin
# By Peter Cooper
#
# Got embedded documents you want to delete? You can delete them as if the
# embedded document collection were an array, but then there's no way to get
# a callback (as far as I could tell). This plugin gives you a call back
# (if you want it) and gives a nicer syntax to deleting embedded docs.
#
# Example:
#
# Let's say we have an Item class that people can "favorite." Favorites are
# stored as embedded items inside User. A "favorited_count" is updated on
# favorite adding/removal.
#
# (I've seen more Mongo-specific techniques at http://www.mongodb.org/display/DOCS/MongoDB+Data+Modeling+and+Rails
# but I haven't tried and don't quite understand them yet..)
#
#   class Item
#     include MongoMapper::Document
#     key :favorited_count, Integer, :default => 0
#   end
#
#   class Favorite
#     include MongoMapper::EmbeddedDocument
#     
#     key :item_id, ObjectId
#     belongs_to :item
#     
#     after_save :update_favorited_count
#     
#     def update_favorited_count
#       return unless new?
#       item.favorited_count += 1
#       item.save
#     end
#     
#     def after_delete
#       item.favorited_count -= 1
#       item.save    
#     end
#   end
#
#   # Assume a fully built "favorite" is in @favorite
#   # Assume "Frank" is a User object
#   Frank.favorites << @favorite
#   @item.reload
#   assert_equal 1, @item.favorited_count
#   @favorite.delete   # <--- the key part here..
#   @item.reload
#   assert_equal 0, @item.favorited_count
#
# Credits
#  - "Pluginized" and extended from example code by Ryan Townsend at http://gist.github.com/280921

module EmbeddedDocumentDelete
  def delete
    rd = _root_document
    assoc = self.class.to_s.underscore.pluralize
    rd.send("#{assoc}=", rd.send(assoc).delete_if { |n| n.id == id })
    rd.save
    after_delete if respond_to?(:after_delete)
  end
end

MongoMapper::EmbeddedDocument.append_inclusions(EmbeddedDocumentDelete)