User class

gistfile1.rb

class User < ActiveRecord::Base
  def following_ids 
    FriendShip.following_ids_for(self) 
  end
  
  def followings
    User.where(:id => following_ids) 
  end
  
  def following?(user)
     FriendShip.following?(self, user) 
  end
  
  def follow!(user)
    FriendShip.follow!(self, user) 
  end
  
  def friend_ids
    FriendShip.friend_ids_for(self) 
  end
  
  def friends
    User.where(:id => friend_ids) 
  end
  
  def follower_ids
    FriendShip.follower_ids_for(self) 
  end
  def followers
    User.where(:id => follower_ids) 
  end
end

gistfile2.rb

class FriendShip

#The datastructure we are working on are SETS, the are unordered lists with unique elements. Perfect for friendships

  #Every "method" in redis is prefixed with the datastructures first letter. SET => s, ergo sMembers. Members in the sets. 
  def self.following_ids_for(user)
    Red.smembers("user:#{user.id}:followings")
  end
  
  def self.follower_ids_for(user)
    Red.smembers("user:#{user.id}:followers")
  end
  
  def self.follow!(user, followed_user)
    return false if user == followed_user
    Red.sadd("user:#{user.id}:followings", followed_user.id)
    Red.sadd("user:#{followed_user.id}:followers", user.id)
    true
  end
  
  def self.following?(user, other_user)
    Red.sismember("user:#{user.id}:followings", other_user.id)
   #Checks if other_user is a user under current_users followings
  end
  
  def self.friend_ids_for(user)
    Red.sinter("user:#{user.id}:followings", "user:#{user.id}:followers")
    #Intersects the two SETS
    # http://www.redis.io/commands/sinter
  end
end

The conventions with Redis are that you use colon as a separator.
user:user_id:followings
The first part can be the model, the table, the second is the pk, the id, an identifier so we can differentiate it, the third part is the attribute, the column, the variable we want out.
So we have stuff like
user:#{user_id}:followings
or
user:#{user_id}:followers

That is a convention, not a strict requirement.