Subscriber needs to follow List Owner but gets error - ruby-on-rails

Question

I have 2 types of users, one is called list_owner and one is called subscriber. These are both users made with devise. Subscribers should be able to follow the list_owner. I have another model called Relationship to keep track who the subscriber follows.
I used http://ruby.railstutorial.org/ mostly as an example.
These are the relations
class Relationship < ActiveRecord::Base
attr_accessible :list_owner_id, :subscriber_id
belongs_to :list_owner
belongs_to :subscriber
end
class ListOwner < ActiveRecord::Base
has_many :messages
has_many :relationships, :dependent => :destroy, :foreign_key => "list_owner_id"
end
class Subscriber < ActiveRecord::Base
has_many :relationships, :foreign_key => "subscriber_id",
:dependent => :destroy
def follow!(list_owner)
puts "-----------------------"
relationships.create!(:subscriber_id => subscriber.id, :list_owner_id => list_owner.id)
end
end
I made a list with list owners with a button where the subscriber can subscribe to.
<%= form_for current_subscriber.relationships.build(:list_owner_id => l.id, :subscriber_id => #subscriber.id),
:remote => true do |f| %>
<%= f.hidden_field :list_owner_id %>
<%= f.hidden_field :subscriber_id %>
<%= f.submit "Subscribe", :class => "button btn" %>
<% end %>
class RelationshipsController < ApplicationController
def create
puts "---------------------relationships CREATE---------------------"
#list_owner = ListOwner.find(params[:relationship][:list_owner_id])
current_subscriber.follow!(#list_owner)
redirect_to root_path
end
end
This is the error i get. What am i doing wrong?
Started POST "/relationships" for 127.0.0.1 at Wed Sep 07 15:37:17 +0200 2011
Processing by RelationshipsController#create as JS
Parameters: {"commit"=>"Subscribe", "relationship"=>{"list_owner_id"=>"2", "subscriber_id"=>"1"}, "authenticity_token"=>"m5plsJLdzuwNt1yKfDJFKD28GcR138V+pezbfbECCPk=", "utf8"=>"✓", "_"=>""}
ListOwner Load (0.2ms) SELECT "list_owners".* FROM "list_owners" WHERE "list_owners"."id" = 2 LIMIT 1
Subscriber Load (0.2ms) SELECT "subscribers".* FROM "subscribers" WHERE "subscribers"."id" = 1 LIMIT 1
Completed 500 Internal Server Error in 34ms
NameError (undefined local variable or method `subscriber' for #<Subscriber:0x102f140c0>):
app/models/subscriber.rb:21:in `follow!'
app/controllers/relationships_controller.rb:8:in `create'

Answer 1

There's no such 'subscriber' object defined, but you don't need one, since you're calling the create!() method on the association collection, which will pre-populate the parent object. That is, calling subscriber.relationships.create! will set subscriber_id = subscriber.id.
def follow!(list_owner)
relationships.create!(:list_owner_id => list_owner.id)
end