stack-level-too-deep.rb

require "rubygems"
require "dm-core"

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

class Category
  include DataMapper::Resource
  
  property :id, Serial
  has n, :items
end

class Item
  include DataMapper::Resource

  property :id, Serial
  property :category_id, Integer
  belongs_to :category
end

DataMapper.auto_migrate!

Item.create(:category_id => 25)
Item.first.category