dm-group_by.rb

module DataMapper
  class Collection
    # A query friendlier group_by method
    def group_by
      assoc = {}
      self.each do |item|
        key = yield(item)
        if assoc.has_key? key
          assoc[key] << item
        else
          q = {}
          item.class.key.each_with_index {|k,i| q[k.name] = item.key[i] }
          assoc[key] = all(q)
        end
      end
      assoc
    end
  end
end