you'll notice that on the call to the second DataMapper.auto_upgrade! there is no "ALTER TABLE" issued to extend the length of the field to varchar(255)

no column length update with #auto_upgrade!

require 'rubygems'
require 'dm-core'
require 'dm-migrations'

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'sqlite:./test.db')

class Post
	include DataMapper::Resource

	property :id, 				Serial
	property :test,				String
	
end


DataMapper.finalize
DataMapper.auto_upgrade!

puts "------------------------------------------------------------------"

class Post
	property :test, 			String, :length => 1..255
end

DataMapper.auto_upgrade!