I'm trying to understand :through and :source with the following example.
I have a User, Job, and Interview models. An interview has an interviewer and interviewee. I would like to use the User model for this and I assume I would have to use :source. Any ideas on where to get started?
Where to start? Keep your user model simple. Think about what your views are going to show, and what the code should look like.
Interview belongs_to :interviewer, :class_name => 'User' belongs_to :interviewee, :class_name => 'User'
User has_many :interviews
This gets tricky, does this join with interviewer_id or interviewee_id in interviews? You probably need two different names for these joins.
User has_many :led_interviews, :class_name => 'Interview', :foreign_key => 'interviewer_id' has_many :attended_interviews, :class_name => 'Interview', :foreign_key => 'interviewee_id'
I find it's best to write some sanity tests to confirm all this. I don't claim that this will work...
Now for the has_many :through join:
Job has_many :interviews has_many :interviewers, :through => :interviews has_many :interviewees, :through => :interviews
This doesn't need a source, because it's going to look at Interview#interviewer or Interview#interviewee by default. Has_many :through associations are unique, they actually look at the other association (the "source" association) and use its reflection data. That's why there's no :class_name or :foreign_key option required. Here's a simple case where :source would be used:
Comment belongs_to :user belongs_to article
Article has_many :comments has_many :users, :through => :comments
In this case, you may not want to use #users. One: it may not be descriptive enough. Another reason is it may be too similar to Article#user, a belongs_to association pointing to the Article's author. So you can do this:
Article has_many :comments has_many :commenters, :through => :comments
Now you'll get some error about ActiveRecord not finding a #commenter or #commenters association on Comment. Of course, it's called #user instead!
Article has_many :comments has_many :commenters, :through => :comments, :source => :user
:class_name was just what I was looking for!
For anyone else interested in this, there is another short write up at