Question: What is the 'has_many' opposite statement for the User model for contactor and contactee?

class Contact < ActiveRecord::Base

  validates_presence_of :project_id, :contactor_id, :contactee_id, :action

  belongs_to :project

  belongs_to :contactor,
             :class_name => "User",
             :foreign_key => "contactor_id"

  belongs_to :contactee,
             :class_name => "User",
             :foreign_key => "contactee_id"

end

-------User model -------

class User < ActiveRecord::Base

  USER_TITLES = [ 'Mr.', 'Mrs.', 'Miss', 'Ms.', 'Dr.', 'Prof.' ]

  validates_presence_of :username, :password, :first_name, :last_name, :email
  validates_uniqueness_of :username

  has_many :addresses
  has_many :projects


  ##
  # model methods

  def self.authenticate(username, password)
    user = User.find(:first, :conditions => ['username = ?', username])
    if user.blank? || password != user.password
      raise "Username or password invalid"
    end
    user
  end

  def self.get_username(user)
    unless user.nil?
      user = User.find(user)
      username = user.username
    end
    username
  end

end