class User < ActiveRecord::Base
  has_and_belongs_to_many :friends, :class_name => 'User', :association_foreign_key => 'friend_id', :join_table => 'friends_users'

  def self.find_common(u1, u2)
    find_by_sql([<<-EOM, u1.id, u2.id])
      SELECT u.*
      FROM users u
      INNER JOIN friends_users fu1 ON fu1.user_id = ? AND fu1.friend_id = u.id
      INNER JOIN friends_users fu2 ON fu2.user_id = ? AND fu2.friend_id = u.id
      ORDER BY u.first_name
    EOM
  end
end