unable to create a model entity with a custom primary key

Hi All, I ran into the following issue today, hope this is the right channel for it. I searched both Lighthouse & Trac and haven't found anything similar.

I'm trying to use a custom primary key. In this case, I'm creating a domain data table for countries. The primary key is the 2 digit ISO 3166 code. Here's my Migration :

class CreateCountries < ActiveRecord::Migration
  def self.up
    create_table :countries, :id => false do |t|
      t.string :country_code, :limit => 2, :null => false
      t.string :name, :null => false

      t.timestamps
    end
    
    add_index :countries, :country_code, :unique => true
  end

  def self.down
    drop_table :countries
  end
end

The database is MySQL (See the end of the ticket for platform versions). The migration runs fine, and creates the right table definition :

mysql> describe countries;
+--------------+--------------+------+-----+---------+-------+
| Field        | Type         | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| country_code | varchar(2)   | NO   | PRI | NULL    |       | 
| name         | varchar(255) | NO   |     | NULL    |       | 
| created_at   | datetime     | YES  |     | NULL    |       | 
| updated_at   | datetime     | YES  |     | NULL    |       | 
+--------------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

Here is my model definition (I've tried both the literal 'country_code' and :country_code with the same results) :

class Country < ActiveRecord::Base
  set_primary_key :country_code
end

Now, here's the unexpected behavior :

$> script/console
Loading development environment (Rails 2.2.2)
>> Country.create(:country_code => "US", :name => "United States")
=> #<Country country_code: 0, name: "United States", created_at: "2009-01-29 01:22:48", updated_at: "2009-01-29 01:22:48">

Here's what is in the log. At the risk of pointing out the obvious, in addition to the warning, the SQL being sent to the DB is missing the country_code.

WARNING: Can't mass-assign these protected attributes: country_code
  SQL (0.2ms)   BEGIN
  Country Create (0.3ms)   INSERT INTO `countries` (`name`, `updated_at`, `created_at`) VALUES('United States', '2009-01-29 01:27:57', '2009-01-29 01:27:57')
  SQL (0.8ms)   COMMIT

If I instead use new & save, things work as expected. Environment Rails : 2.2.2 Ruby : ruby 1.8.6 (2008-03-03 patchlevel 114) [i686-darwin9.5.0] MySQL : mysql5 Ver 14.12 Distrib 5.0.67, for apple-darwin9.5.0 (i686) using EditLine wrapper OS : OSX 10.5.6