One of the things I like about datamapper over activerecord is that all the attributes of the model are listed in the model itself. I found something today that can help to bridge that gap in a small way.
Have a look at annotate-models you can install it as a gem
gem install annotate-models
Then go into your project directory and run annotate, you will then have something like this at the top of each model.
# == Schema Information
# Schema version: 20090130210328
#
# Table name: profiles
#
# id :integer(4) not null, primary key
# user_id :integer(4)
# first_name :string(255)
# last_name :string(255)
# website :string(255)
# blog :string(255)
# flickr :string(255)
# about_me :text
# location :string(255)
# is_active :boolean(1)
# last_activity_at :datetime
# created_at :datetime
# updated_at :datetime
#