stack overflow in datamapper

userrelationshipmodel-dm.rb

# SystemStackError: stack level too deep
#	from /Users/name/.rvm/rubies/ruby-1.9.2-#p290/lib/ruby/1.9.1/irb/workspace.rb:80
#Maybe IRB bug!!

class User
	include DataMapper::Resource

	property :id,    Serial
	property :email, String, :length => 255#, :required => true

	has n, :relationships
	has n, :followers, :through => :relationships, :model => 'User',
	       :child_key => [:user_id]
        has n, :follows, :through => :relationships, :model => 'User',
               :via => :user, :child_key => [:follower_id]
end

class Relationship
  include DataMapper::Resource

  property :user_id, Integer, :key => true
  property :follower_id, Integer, :key => true
  
  belongs_to :user, :child_key => [:user_id]
  belongs_to :follower, :model => 'User', :child_key => [:follower_id]
end