gistfile1.rb

class User < ActiveRecord::Base
  # Columns:
  # id,     integer
  # my_id,  string
  # etc...
  
  has_one :contact, :primary_key => "my_id", :foreign_key => "my_id"
end

class Contact < ActiveRecord::Base
  # Columns:
  # id,     integer
  # my_id,  string
  # etc...
  
  belongs_to :user, :primary_key => "my_id", :foreign_key => "my_id"
end



### Get a reference to a user
>> user = User.first
  User Load (0.3ms)   SELECT * FROM "users" LIMIT 1
=> #<User id: 1, my_id: "54feb156">

### Does the user have a contact associated? No.
>> user.contact
  Contact Load (0.2ms)   SELECT * FROM "contacts" WHERE ("contacts".my_id = '54feb156') LIMIT 1
=> nil

### Give the user a contact
>> user.contact = Contact.new
  Contact Load (0.1ms)   SELECT * FROM "contacts" WHERE ("contacts".my_id = '54feb156') LIMIT 1
  Contact Create (0.6ms)   INSERT INTO "contacts" ( "my_id" ) VALUES('54feb156')
=> #<Contact id: 12, my_id: "54feb156">

### Does the user have a contact associated? Yes!
>> user.contact
=> #<Contact id: 12, my_id: "54feb156">

### Save the user. Contact's my_id is set to user's id!?
>> user.save
  User Update (0.8ms)   UPDATE "users" SET "perishable_token" = '0BIrKc54inzvSQhAc2uq' WHERE "id" = 1
  Contact Update (0.1ms)   UPDATE "contacts" SET "updated_at" = '2009-09-01 17:55:46', "my_id" = 1 WHERE "id" = 12


###
### Why is "my_id" set to 1 in the above update?
###