Polymorphic relationship vs STI vs Class table inheritance with RoR

Question

There are three types of invoice items with following tables

1) SubscriptionItems,

2) Prorations,

3) UsageItems,

Those have the same attributes below

invoice_id
amount
stripe_invoie_id

However

only SubscriptionItem and Proration

period_start_at
period_end_at

and only Proration and UsageItem has

title

and only UsageItem has

uuid
account_id
description

To achieve this model I've been using polymorphic relation.

class InvoiceItem < ActiveRecord::Base
  belongs_to :invoice
  belongs_to :itemable, polymorphic: true
end

class SubscriptionItem < ActiveRecord::Base
  belongs_to :plan
  has_one :invoice_item, as: :itemable
end

class UsageItem < ActiveRecord::Base
  belongs_to :account
  has_one :invoice_item, as: :itemable
end

class Invoice < ActiveRecord::Base
  belongs_to :account
  has_many :invoice_items
end

class Account < ActiveRecord::Base
  has_many :invoices
  has_many :usage_items
end

For now it works. However As far as I understand polymorphic should have has_many relation. So this resides in the middle of Polymorphic and STI. Because those three types of invoice items are always be subscriptionitem, proration, or usageitem.

It's hard decision that I could keep using this models (polymorphic with has_one) or should I use STI instead? Or class table inheritance should be fit?

EDIT

I'd love to hear the reason why I could use some design. Maybe those types pros and cons.

As far as I know,

If I apply STI

That leads many NULLable columns, but RoR supports STI. So it's easy to use.

If I apply polymorphic with has_one

It stills the rails way but the original polymorphic definition is different. It should have has_many relationship instead of has_one. Also it's impossible to add foreign key.

Ref: Blog post for STI to polymorphic

If I apply Class table inheritance,

It's more efficient for relational database, but it's not rails way.

Ref: Blog post for STI to class table inheritance

Crashtor Crashtor · Accepted Answer · 2017-02-11T15:55:22

I think STI with a hidden_field passing the appropriate value for each attribute that should determine the invoice type, could be the way to go here. It's simple and efficient.

Let's say you added a field called :invoice_type to your invoice model,

Then just loop through the items in an array like (Rough example):

<% @invoices.where(:invoice_type => "proration").find_each do |invoice| %>
   <% @invoices.where(:start_date => "#{@invoice.start_date}").find_each do |invoice| %>
         <!--Will only show the start_date of invoices where the invoice_type is propration. -->
    <% end %>
<% end %>

Polymorphic relationship vs STI vs Class table inheritance with RoR

1 Answers