gistfile1.rb

require 'rubygems'
require 'dm-core'

class Event
  include DataMapper::Resource
  
  default_scope.update( :order => [ :start_time.desc ] )

  property :id,               Serial
  property :eid,              String
  property :name,             String, :length => 255
  property :tagline,          String, :length => 255
  property :start_time,       Integer
  property :end_time,         Integer
  property :location,         String, :length => 255
  property :description,      Text

end


DataMapper::Logger.new(STDOUT)
DataMapper.setup(:default, "sqlite3::memory:")
DataMapper.auto_migrate!

Event.create( :eid => "abc" )
Event.create( :eid => "def" )
Event.create( :eid => "abc" )

p Event.all( :fields => [:eid] , :unique => true )
# => TypeError: can't modify frozen object

p Event.all( :fields => [:id,:eid] , :unique => true )
# Works!