gistfile1.rb

class CoursePrerequisite < ActiveRecord::Base
  belongs_to :course
  belongs_to :prerequisite, :class_name => 'Course'

  attr_accessible :required
  belongs_to :suggested_by, :class_name => 'User'
end

class Course
  has_many :course_prerequisites
  has_many :prerequisites, :class_name => 'Course', :through => :course_prerequisites, :dependent => :destroy
end