Rails has_and_belongs_to_many关联

class User < ActiveRecord::Base
  has_and_belongs_to_many :followed_courses,  :class_name => \"Course\"
end

class Course < ActiveRecord::Base
  has_and_belongs_to_many :followers, :class_name => \"User\"
end

  def following_course?(course)
    followed_courses.include?(course)
  end

  def follow_course!(course)
    followed_courses<<course
  end

  def unfollow_course!(course)
    followed_courses.delete(course)
  end

= form_for @course, :url => { :action => \"follow\" }, :remote => true do |f|
  %div= f.hidden_field :id
  .actions= f.submit \"Follow\"

  def follow
    @course = Course.find(params[:id])
    current_user.follow_course!(@course)
    respond_to do |format|
      format.html { redirect_to @course }
      format.js
    end
  end