friendships_schema.sql

friendship.rb

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => "User"
  validates_presence_of :friend_id
  validates_presence_of :user_id
  validates_inclusion_of :accepted, :in => [true, false]
  validates_uniqueness_of :friend_id, :scope => [:user_id]
  validate :unique_friendship_record, :cannot_be_own_friend
  attr_accessible :user_id, :friend_id
  
  def unique_friendship_record
    errors.add(:base, "Friendship record must be unique") if Friendship.for(friend_id, user_id).first
  end
  
  def cannot_be_own_friend
    errors.add(:base, "Cannot be your own friend") if friend_id == user_id
  end
  
  scope :for, lambda {|a,b| 
    where("(friend_id = :one and user_id = :two)
           or (user_id = :one and friend_id = :two)", 
           :one => a, :two => b)}
           
  scope :accepted, where("accepted")
  
end

friendships_controller.rb

  def create
    @friendship = Friendship.where(:friend_id => current_user.id, :user_id => params[:user_id]).first
    if @friendship
      @friendship.accepted = true
    else
      @friendship = current_user.friendships.build(:friend_id => params[:user_id])
    end
    if @friendship.save
      flash[:success] = "Added friend."
      redirect_to params[:return_to] || root_url
    else
      flash[:error] = "Unable to add friend."
      redirect_to params[:return_to] || root_url
    end
  end

gistfile1.txt

                                    Table "public.friendships"
   Column   |            Type             |                        Modifiers                         
------------+-----------------------------+----------------------------------------------------------
 id         | integer                     | not null default nextval('friendships_id_seq'::regclass)
 user_id    | integer                     | not null
 friend_id  | integer                     | not null
 created_at | timestamp without time zone | 
 updated_at | timestamp without time zone | 
 accepted   | boolean                     | not null default false