Question

I have the following two models, User..

class User < ActiveRecord::Base
  has_and_belongs_to_many :sites
end

.. and Site:

class Site< ActiveRecord::Base
  has_and_belongs_to_many :users
end

Up to this point its fine. It works and it’s pretty simple.
Now I want to introduce “primary user” to the Site. I add “primary_user_id” to the Site, and trying to add a second association:

class Site< ActiveRecord::Base
 has_and_belongs_to_many :user

 # my new association that doesn't work...
 has_one :primary_user, :class_name => "User", :conditions => ['id = ?', '{self.primary_user_id}'] 
end

It doesn’t like it… Now I know that I can fake this by just adding a method “primary_user” to the site and this will work, but my question is whether it is possible to user ActiveRecord associations and how?

Answer 1

has_and_belongs_to_many is tricky and most people have moved away from it and use has_many through => model.
btw – ‘Up to this point its fine. It works and it’s pretty simple.’ is how all things start off. How they perform when you ‘really’ start to use them is what counts and for that reason you’ll probably find has_many through easier to work with.

These links will help:

http://paulbarry.com/articles/2007/10/24/has_many-through-checkboxes

http://thoughtsincomputation.com/posts/checkboxes-with-has_many-through

http://my.opera.com/durrantm/blog/2011/07/24/rails-simple-form-with-has-many-through-hmt-relationship

https://github.com/romanvbabenko/nested_has_many_through (nesting gem).