# config/init.rb
dependency "dm-validations"

# model
class Author
  include DataMapper::Resource
  property :email, String, :nullable => false, :unique => true, :format => :email_address, :key => true
end

>> a1 = Author.fixtures[0]
=> #
>> a1.save
=> true
>> a2 = a1.dup
=> #
>> a2.save
=> false
>> a2.errors
=> #