Enterprise Rails

Strategy Pattern with Domain Tables

Another use of domain tables, when the number of records is tractable enough to be represented in code, is to point to collections of methods or data contained in classes, much as a trigger for the Gang of Four strategy pattern.

We will explore this idea with the payment types found in the orders table. We begin with the standard domain table refactoring performed earlier. Then, we’ll enhance our solution by making use of ActiveRecord’s single table inheritance, to achieve the Domain Table Strategy Pattern. We start out with our initial cut at the Order class, before we create the domain table for payment types. It looks very similar to our initial Ratings class, with an array containing the acceptable payment types to match the database constraint:

class Order < ActiveRecord::Base
  belongs_to :movie_showtime_id
  validates_uniqueness_of :confirmation_code
  validates_presence_of :confirmation_code,
    :purchaser_name, :payment_type,
    :credit_card_number, :credit_expiration_month, :credit_expiration_year

  PAYMENT_TYPES = ['Visa', 'MasterCard', 'American Express']

  def validate_payment_type
    unless PAYMENT_TYPES.include?(payment_type)
      errors.add('payment_type',
        "must be #{PAYMENT_TYPES[0..-2].join(', ')} or #{PAYMENT_TYPES[-1]}")
  end

  def validate
    validate_payment_type
  end
end

Following the ratings example, we factor out the payment type into its own table, payment_types, and we insert the appropriate data for our domain of credit card processing:

create sequence ...