composite_primary_keysではvarcharがダメなの？

とりあえずテストケースをざーっと読んでみた。set_primary_keysを使っているのは以下の四つ。クラスとDDLをセットで挙げます。

class ProductTariff < ActiveRecord::Base
	set_primary_keys :product_id, :tariff_id, :tariff_start_date
	belongs_to :product, :foreign_key => :product_id
	belongs_to :tariff,  :foreign_key => [:tariff_id, :tariff_start_date]
end

CREATE TABLE `product_tariffs` (
  `product_id` int(11) NOT NULL,
  `tariff_id` int(11) NOT NULL,
  `tariff_start_date` date NOT NULL,
  PRIMARY KEY  (`product_id`,`tariff_id`,`tariff_start_date`)
) TYPE=InnoDB;

class ReferenceCode < ActiveRecord::Base
  set_primary_keys :reference_type_id, :reference_code
  
  belongs_to :reference_type, :foreign_key => "reference_type_id"
  
  validates_presence_of :reference_code, :code_label, :abbreviation
end

CREATE TABLE `reference_codes` (
  `reference_type_id` int(11) NOT NULL,
  `reference_code` int(11) NOT NULL,
  `code_label` varchar(50) default NULL,
  `abbreviation` varchar(50) default NULL,
  `description` varchar(50) default NULL,
  PRIMARY KEY  (`reference_type_id`,`reference_code`)
) TYPE=InnoDB;

class Suburb < ActiveRecord::Base
  set_primary_keys :city_id, :suburb_id
  has_many :streets,  :foreign_key => [:city_id, :suburb_id]
end

CREATE TABLE `suburbs` (
  `city_id` int(11) NOT NULL,
  `suburb_id` int(11) NOT NULL,
  `name` varchar(50) NOT NULL,
  PRIMARY KEY  (`city_id`,`suburb_id`)
) TYPE=InnoDB;

class Tariff < ActiveRecord::Base
	set_primary_keys [:tariff_id, :start_date]
	has_many :product_tariffs, :foreign_key => [:tariff_id, :tariff_start_date]
	has_one :product_tariff, :foreign_key => [:tariff_id, :tariff_start_date]
	has_many :products, :through => :product_tariffs, :foreign_key => [:tariff_id, :tariff_start_date]
end

CREATE TABLE `tariffs` (
  `tariff_id` int(11) NOT NULL,
  `start_date` date NOT NULL,
  `amount` integer(11) default NULL,
  PRIMARY KEY  (`tariff_id`,`start_date`)
) TYPE=InnoDB;

というわけで、intとdateはオッケーだけど、PKにvarcharダメなんじゃねーの疑惑が発生。この疑惑を現在調査中。