create_table "animal_friends", :force => true do |t|
    t.integer  "animal_id"
    t.integer  "animal_friend_id"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "status_id",        :default => 1
  end

SELECT animals.*
from animals join animal_friends as af
  on animals.id =
    case when af.animal_id = #{id} then af.animal_friend_id else af.animal_id end
WHERE #{id} in (af.animal_id, af.animal_friend_id)

has_many :friends, :class_name => "Animal", :finder_sql => 'SELECT animals.* from animals join animal_friends as af on animals.id = case when af.animal_id = #{id} then af.animal_friend_id else af.animal_id end ' +
 'WHERE #{id} in (af.animal_id, af.animal_friend_id) and status_id = #{Status::CONFIRMED.id}'

@animal.friends.first

CREATE VIEW with_inverse_animal_friends (
  SELECT id,
         animal_id,
         animal_friend_id,
         created_at,
         updated_at,
         status_id
    FROM animal_friends
   UNION
  SELECT id,
         animal_friend_id AS animal_id,
         animal_id AS animal_friend_id,
         created_at,
         updated_at,
         status_id
    FROM animal_friends
)

CREATE VIEW unique_animal_friends (
  SELECT MIN(id), animal_id, animal_friend_id, MIN(created_at), MAX(updated_at), MIN(status_id)
    FROM
   (SELECT id,
           animal_id,
           animal_friend_id,
           created_at,
           updated_at,
           status_id
      FROM animal_friends
     UNION
    SELECT id,
           animal_friend_id AS animal_id,
           animal_id AS animal_friend_id,
           created_at,
           updated_at,
           status_id
      FROM animal_friends) AS all_animal_friends
  GROUP BY animal_id, animal_friend_id
)

class Animal < ActiveRecord::Base
  has_many :unique_animal_friends
  has_many :friends, :through => :unique_animal_friends
end

class UniqueAnimalFriend < ActiveRecord::Base
  belongs_to :animal
  belongs_to :friend, :class_name => "Animal"
end