Ruby on Rails

I have installed the latest version of rails and jruby. I have copied
all my files from rails 2.3.5 version and am trying to bring all to work
in this version

Project.rb
------------------
class Project < ActiveRecord::Base
 has_and_belongs_to_many :people
 has_many :documents, :conditions => ["project_id =?", self.id ]
..
..
end

application_helper.rb
--------------------------

def find_projects
    user = Person.find(session[:userid])
   projects = Project.find(:all)
   ..
..
..
end

I am getting an error
undefined method `id' for #<Class:0x182237ac>  (self.id is the problem
guess)

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