gistfile1.txt

module Habtm
  def self.included(model)
    model.extend ClassMethods
  end
  
  module ClassMethods
    def habtm(name, opts = {})
      klass = opts.delete(:model) || name.to_s.classify
      resource_klass = [klass, self].map{|k| k.to_s }.sort.join('')
      storage_name = Extlib::Inflection.tableize(resource_klass)
      field = name.to_s.singular
      self_klass = self.to_s.snake_case
      has n, storage_name.to_sym
      resource = DataMapper::Model.new(storage_name)
      resource.property :"#{self_klass}_id", Integer, :key => true, :unique => [ :"#{field}_id" ]
      resource.property :"#{field}_id", Integer, :key => true
      resource.belongs_to :"#{self_klass}"
      resource.belongs_to :"#{field}"
      begin 
        Object.const_get(resource_klass) 
      rescue
        Object.const_set(resource_klass, resource)
      end
      class_eval <<-RUBY
        def #{name}
          #{klass}.all(:id => #{field}_ids)
        end
        
        def #{field}_ids
          @#{field}_ids = #{resource_klass}.all(:#{self_klass}_id => self.id, :fields => [ :#{field}_id ] ).map{|r| r.#{field}_id }
        end
        
        def #{name.to_s.singular}_ids=(ids)
          ids = ids.split(',') if ids.is_a?(String)
          old_ids = #{field}_ids
          (old_ids - ids).each do |remove_id|
            #{resource_klass}.first(:#{field}_id => remove_id, :#{self_klass}_id => self.id).destroy
          end
          (ids - old_ids).each do |add_id|
            #{storage_name} << #{resource_klass}.new(:#{field}_id => add_id, :#{self_klass}_id => self.id)
          end
          @#{field}_ids = ids
        end
      RUBY
    end
  end
end