Rails - May 2006 - Self-referential MtoM implementation

ok, guys i have followed the self referential recipe from the book it 
works perfect but now i have some doubts, at the end the model are 
modified to force the user beign added as a friend that add too who are 
adding him so how i can make that the full relationship doesn?t be 
complete until the friend beign added approves it(talking in the 
implementation of the code of course)?

by the way, here is the code:

class AddPeopleAndTheirFriendsRelationship < ActiveRecord::Migration
  def self.up
    create_table :people do |t|
      t.column "name", :string
    end
    create_table :friends_people do |t|
      t.column "person_id", :integer
      t.column "friend_id", :integer
    end
  end
  def self.down
    drop_table :people
    drop_table :friends_people
  end
end

class Person < ActiveRecord::Base
  has_and_belongs_to_many :friends,
    :class_name => "Person",
    :join_table => "friends_people",
    :association_foreign_key => "friend_id",
    :foreign_key => "person_id",
    :after_add => :be_friendly_to_friend,
    :after_remove => :no_more_mr_nice_guy
  def be_friendly_to_friend(friend)
    friend.friends << self unless friend.friends.include?(self)
  end
  def no_more_mr_nice_guy(friend)
    friend.friends.delete(self) rescue nil
  end
end

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