gistfile1.rb

require 'rubygems'
gem 'dm-core', '0.10.2'
gem 'do_sqlite3', '0.10.0'
require 'dm-core'

class Author
  include DataMapper::Resource
  
  property :id, Serial
  property :name, String
  
  has n, :posts
end

class Post
  include DataMapper::Resource
  
  property :id, Serial
  property :body, Text
  property :author_id, String
  
  belongs_to :author
end

DataMapper.setup(:default, 'sqlite3::memory:')

DataMapper.auto_migrate!

author = Author.create(:name => 'Alice', :id => '1')
author.posts.create(:body => 'Hello World')

# doesn't work becuase :author_id is a String
Post.first.author # => nil

Post.property :author_id, Integer
# works because :author_id is an Integer
Post.first.author # => #<Author @id=1 @name="Alice">