countries primary_key

I'm using:

ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore

per a design spec that I cannot change.

I wanted to create a countries table, here is my migration:

class CreateCountries < ActiveRecord::Migration

  def self.up     create_table :countries, :primary_key => :country_id, :force => true do |t|       t.string :country_name, :null => false, :limit => 48     end     add_index :countries, :country_name, :unique => true, :name => 'countries_country_name'   end

  def self.down     drop_table :countries   end end

When I run my countries migration I get:

rake db:migrate

(in /rails/foo) == CreateCountries: migrating ================================================ -- add_column("countries", :country_id, :primary_key, {:precision=>nil, :scale=>nil, :limit=>nil, :null=>nil, :default=>nil}) rake aborted! An error has occurred, all later migrations canceled:

OCIError: ORA-30649: missing DIRECTORY keyword: ALTER TABLE countries ADD country_id NUMBER(38) NOT NULL PRIMARY KEY DEFAULT NULL

(See full trace by running task with --trace)

Any ideas?