Question

I’m about to use STI in my Rails 2.3 application.

I’ve modeled it the following way:

Base Class:

class Tariff < ActiveRecord::Base
  def self.inherited(child)
    child.instance_eval do
      def model_name
        Tariff.model_name
      end
    end
    super
  end

  def self.select_options
    descendants.map { |c| c.to_s }.sort
  end
end

Its subclasses:

class FlatRateTariff < Tariff
end

class TimeOfUseTariff  < Tariff
  has_many :tariffing_periods, :dependent => :destroy
  accepts_nested_attributes_for :tariffing_periods, :allow_destroy => true
end

When I am trying to create a form_for :tariff I’m getting an undefined method `tariffing_periods’ for Tariff. How should I go about modeling this scenario? Should I put has_many association on the parent class?

Answer 1

STI is usually done in Rails like this:

class Tariff < ActiveRecord::Base
end

class FlatRateTariff < Tariff
end

class TimeOfUseTariff < Tariff
end

Make sure that the Tariff table has an attribute type:string – that’s where ActiveRecord stored the class name

You don’t need this: (instead you can check .class )

 def self.inherited(child)
    child.instance_eval do
      def model_name
        Tariff.model_name
      end
    end
    super
  end

here’s more info:

page 373 in Agile Web Development with Rails, 3rd edition

or:
http://my.safaribooksonline.com/book/web-development/ruby/9780132480345/advanced-active-record/ch09lev1sec5