gistfile1.txt

irb(main):001:0> class User;include DataMapper::Mongo::Resource;end
=> User
irb(main):006:0> User.property :id, DataMapper::Mongo::Types::ObjectID
=> #<DataMapper::Property @model=User @name=:id>
irb(main):003:0> User.property :stuff, DataMapper::Mongo::Types::Array
=> #<DataMapper::Property @model=User @name=:stuff>
irb(main):004:0> User.class_eval "def foo; puts Array.new;end"
=> nil
irb(main):007:0> User.new.foo
#<DataMapper::Mongo::Types::Array:0xb73383dc>
=> nil