require "rubygems"
require "dm-core"

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

class Post
  include DataMapper::Resource
  property :ID, Integer, :serial => true
end

class Comment
  include DataMapper::Resource
  property :comment_ID, Integer, :serial => true
  property :comment_post_ID, Integer
  property :text, String
end

DataMapper.auto_migrate!

# You have to do has n, belongs_to AFTER auto_migrate otherwise it creates a post_id field for you.

### @export "custom-keys"
class Post
  has n,       :comments, 
               :parent_key => [:ID], 
               :child_key => [:comment_ID]
end

class Comment
  belongs_to   :post, 
               :parent_key => [:comment_post_ID], 
               :child_key => [:comment_ID]
end
### @end

post = Post.create
post.comments << Comment.create(:text => 'xx')
post.save

puts Post.first.comments.first.inspect