Question

When one table has 2 columns which refer same master table with ActiveRecord on Rails3

There are tables like below.

Depts  
  id 
  dept_name 

Users 
  id 
  dept_id 
  previous_dept_id 

Users table has two columns which refer Depts table.
How can I get dept_name for each columns?

class Dept < ActiveRecord::Base 
  has_many :user 
end 

class User < ActiveRecord::Base 
  belongs_to :dept 
end 

Answer 1

I think what you’re looking for is the following:

class User < ActiveRecord::Base 
  belongs_to :dept 
  belongs_to :previous_dept, :class_name => 'Dept', :foreign_key => 'previous_dept_id'
end

You should then be able to access the two departments like this:

dept_name = user.dept.dept_name
previous_dept_name = user.previous_dept.dept_name

It’s important to note that your Dept model will only find users by the dept_id column. I think you’d have to add a second has_many to Dept if you needed to find users by their previous dept. Something like:

class Dept < ActiveRecord::Base 
  has_many :user 
  has_many :previous_user, :class_name => 'User', :foreign_key => 'previous_dept_id'
end