trustieforge/app/models/students_for_course.rb

class StudentsForCourse < ActiveRecord::Base
  attr_accessible :course_id, :student_id
  
  belongs_to :course, :class_name => 'Course', :foreign_key => :course_id

  belongs_to :student, :class_name => 'User', :foreign_key => :student_id
  
  validates_presence_of :course_id, :student_id
  validates_uniqueness_of :student_id, :scope => :course_id
  
end