Why polymorphic association doesn't work for STI if type column of the polymorphic association doesn't point to the base model of STI?

Question

I have a case of polymorphic association and STI here.

# app/models/car.rb
class Car < ActiveRecord::Base
  belongs_to :borrowable, :polymorphic => tru         


        

Answer 1

This is how I solved that problem using aforementioned hints:

# app/models/concerns/belongs_to_single_table_polymorphic.rb

module BelongsToSingleTablePolymorphic
  extend ActiveSupport::Concern

  included do
    def self.belongs_to_sti_polymorphic(model)
      class_eval "belongs_to :#{model}, polymorphic: true"
      class_eval 'before_validation :set_sti_object_type'

      define_method('set_sti_object_type') do
        sti_type = send(model).class.name

        send("#{model}_type=", sti_type)
      end
    end
  end
end

and with that, for any model in which I would find belongs_to :whatever, polymorphic: true I do:

class Reservation < ActiveRecord::Base
  include BelongsToSingleTablePolymorphic
  # .....
  belongs_to_sti_polymorphic :whatever
  # .....
end