Kenneth-KT / safe_sti

Prevent ActiveRecord STI + autoloading inconsistent behavior

Safe STI

This Gem makes ActiveRecord's STI (Single Table Inheritance) feature play nice with eager loading by enforcing the developers to write out direct STI child classes and automatically eager load the entire STI hierarchy whenever a STI class is loaded, to prevent inconsistent behavior in queries.

Learn more about the problems of using Autoloading + STI: https://guides.rubyonrails.org/autoloading_and_reloading_constants.html#single-table-inheritance

Usage

Let say you have the following class hierarchy:

Cat < Animal < Thing < ApplicationRecord

Dog < Animal < Thing < ApplicationRecord

First, install this gem and enable Safe STI checking for ApplicationRecord: app/models/appliaction_record.rb:

 class ApplicationRecord
   self.abstract_class = true
+  SafeSti.enable_for self
   ...<your code>...
 end

In STI models, declare the list of direct subclasses with safe_sti_child { <KLASS> } format: app/models/thing.rb:

 class Thing < AppliactionRecord
+  safe_sti_child { Animal }
  ...<your code>...
 end

app/models/animal.rb:

 class Animal < Thing
+  safe_sti_child { Cat }
+  safe_sti_child { Dog }
  ...<your code>...
 end

or

 class Animal < Thing
+  safe_sti_child { [Cat, Dog] }
  ...<your code>...
 end

Then you can try to add a new subclass without definiting it using safe_sti_child. app/models/unicorn.rb:

+class Unicorn < Animal
+end

In your console, run: Unicorn.new or Unicorn.find(1) will result in warning being emitted as follow:

Missing `safe_sti_child { Unicorn }` inside class body of Animal class

The developer will need to follow the instruction provided to eliminate the warning: app/models/animal.rb:

 class Animal < Thing
   safe_sti_child { Cat }
   safe_sti_child { Dog }
+  safe_sti_child { Unicorn }
   ...<your code>...
 end

In this way, your STI model hierarchy will always be full loaded, preventing the inconsistent query result caused by lazy class loading.