Odd ActiveRecord behavior - behaves differently based on order of associations

Question

I've found pretty odd behavior of rails's activerecord. This occurs in rails 2.3.9 and does not in rails 3.

Here is how you can reproduce it. (Or just clone github repo example I created: git clone git://github.com/gonchs/rails-2.3.9-odd-association-behavior-example.git )

class User < ActiveRecord::Base
  has_one :parent
  has_one :contact, :through => :parent
end

class Contact < ActiveRecord::Base
  has_one :parent
  has_one :user, :through => :parent
end

class Parent < ActiveRecord::Base
  belongs_to :user
  belongs_to :contact
end

Try it for yourself. In the first example, everything goes as it should. In the second, it behaves unexpectedly.

open up script/console and do:

user = User.new
user.contact = Contact.new
user.parent = Parent.new
user.contact
=> #<Contact id: nil, created_at: nil, updated_at: nil> 

user = User.new
user.parent = Parent.new
user.contact = Contact.new
user.contact
=> nil

Any ideas why is this happening? Is it a bug or am I missing something here?

Answer 1

There seems to be redundancy in the models... the associations seem a little off...

Depending on where the actual foreign keys are in the tables, I would take out either the through or has_one...

class User < ActiveRecord::Base
  has_one :parent
end

class Contact < ActiveRecord::Base
  has_one :user, :through => :parent
end

class Parent < ActiveRecord::Base
  belongs_to :user
  belongs_to :contact
end