class file

testclasses.rb

class Expense
  include MongoMapper::Document
  key :expense_id, ObjectId
  key :amount, Float #FloatToDecimalPrecision
  key :date, Time
  key :notes, String
  key :tags, Array # => company 
  key :type, String 
end

class ExpenseCubicle
  extend Cubicle::Aggregation
  dimensions :tags, :expression=>'this.tags[0]'
 #dimensions :tags, :expression=>'this.tags.first' #=> also failed 
end