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In my project, I have a relationship model that allow users to follow each other. 

class Relationship < ActiveRecord::Base
  attr_accessible :followed_id

  belongs_to :follower, :class_name => "User"
  belongs_to :followed, :class_name => "User"

end

Now, I want to also allow users to follow courses and groups. Do I start a new followedCourse and followedGroup model or do I make the relationship model polymorphic? How do I do that? Thanks.

randomor
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1 Answers1

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I wouldn't use polymorphic for potentially-large tables. I think the best way to go is to use has_and_belongs_to_many relationships for this kind of relation.

Remember to create indexes on user_id, group_id to speed up things a bit. You can do that by using add_index(:table_name,[:user_id,:group_id]).

I would also make the relation UNIQUE, which you can do appending :unique => true at the end of the add_index command.

Lucas d. Prim
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  • forgot to link you to a `has_and_belongs_to_many` proper explanation. Here it goes: [link](http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_and_belongs_to_many) – Lucas d. Prim Apr 14 '11 at 00:29
  • Thanks Lucas, that solved my problem. And I was reading about it at the rails guides. But your link is even more helpful! :) – randomor Apr 14 '11 at 00:51
  • One question though, i need to follow and unfollow specific courses&groups. But I won't have a model for that. Do I just use user model to do that? Like: `def following?(followed) courses_users.find_by_user_id(followed) end` – randomor Apr 14 '11 at 00:57
  • exactly! In this case you want to ask an `User` if he follows a course. You're following the right path! – Lucas d. Prim Apr 14 '11 at 01:03
  • and since an `User` `has_and_belongs_to_many :courses` you can ask if he follows a course this way: `User.new.courses.include?(course_instance)` – Lucas d. Prim Apr 14 '11 at 01:04
  • i think i got a new problem here. since the courses are created by the users, it already belongs_to user. so when I use user.courses after I add has_and_belongs_to_many, it is in conflict with the user.courses method from before. – randomor Apr 14 '11 at 04:16
  • I've used `has_and_belongs_to_many :followed_courses, :class_name => "Course"` looks like working. :) – randomor Apr 14 '11 at 04:27