class Account < ActiveRecord::Base
  has_one :contact, :as => :primary_contact
  has_many :contacts
  has_one :payment_method, :as => :default_payment_method
  has_many :telephone_handlers
  has_many :mail_handlers
end

class Contact < ActiveRecord::Base
  belongs_to :account
  has_one :address, :as => :primary_postal_address
  has_many :addresses
  has_one :telephone_number, :as => :primary_telephone_number
  has_many :telephone_numbers
  has_one :email_address, :as => :primary_email_address
  has_many :email_addresses
end

Mysql::Error: Unknown column 'payment_methods.default_payment_method_id' in 'where clause': SELECT * FROM `payment_methods`     WHERE (`payment_methods`.default_payment_method_id = 5 AND `payment_methods`.default_payment_method_type = 'Account')  LIMIT 1