should_this_work.rb

class Accounting::LedgerItem < ApplicationRecord
  # super class
  has_many :line_items, class_name: 'Accounting::LineItem', as: :ledger_item

  # specific line items
  has_many :ordered_items, class_name: 'Accounting::LineItems::OrderedItem', as: :ledger_item
  has_many :fees, class_name: 'Accounting::LineItems::Fee', as: :ledger_item
  has_many :payments, class_name: 'Accounting::LineItems::Payment', as: :ledger_item
  has_many :discounts, class_name: 'Accounting::LineItems::Discount', as: :ledger_item
end

class Accounting::LineItem < ApplicationRecord

  belongs_to :ledger_item, class_name: 'Accounting::LedgerItem'
  
end

class Accounting::LineItems::OrderedItem < Accounting::LineItem

end

class Accounting::LineItems::Discount < Accounting::LineItem

end

class Accounting::LineItems::Fee < Accounting::LineItem

end

class Accounting::LineItems::Payment < Accounting::LineItem

end

li = Accounting::LedgerItem.new
li.order_items.build()
li.line_items.must_equal 1