A brief model of Friendship in ActiveRecord

friends.rb

# users
# id | name | email

class User < ActiveRecord::Base
  has_many :friendships
  has_many :friends, through: :friendships

  def friends
    User.join(:friendships).where('friendships.user_id = ? OR friendships.friend_id = ?', self.id, self.id)
  end
end

# friendships
# id | user_id | friend_id

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, class_name: 'User'
end