lhoeg / rails-sti-enum

Testing Rails STI using Enum for type field

Rails STI using Rails Enums

Having used Rails STI many times, I came to wonder if it was possible (not necessarily feasible or in any way sane) to use Rails Enum instead of a simple String field for STI type.

It seems it is, although with a tiny tweak to set the type on creation :)

Drawbacks: Manually edit Enum values to add new class.

Note: Should explicitly map enum values' integer mapping to avoid disaster when adding/removing types!

Initial Ruby and Rails versions

mkdir rails-sti-enum
cd rails-sti-enum
git init

echo "2.3.0" > .ruby-version

cat > Gemfile <<-EOF
source 'https://rubygems.org'
ruby '2.3.0'

gem 'rails', '>= 5.0.0.rc1', '< 5.2'
EOF
git add .ruby-version Gemfile
git commit -m "initial commit"

bundle install
git add Gemfile.lock
git commit -m "initial gems"

Create the Rails application

bundle exec rails new .
git add .
git commit -m "rails new"

Create a model to play with

bin/rails g model Animal name type:integer
bin/rails db:migrate

Create a few other models;

mkdir app/models/animal
cat > app/models/animal/cat.rb <<-EOF
class Animal::Cat < Animal
end
EOF

cat > app/models/animal/dog.rb <<-EOF
class Animal::Dog < Animal
end
EOF

Enable Enums as STI type in app/models/animal.rb

class Animal < ApplicationRecord
  before_create :set_type
  enum type: { 'Animal::Cat' => 0, 'Animal::Dog' => 1 }

  private

  # Unfortunately type is not set by rails...
  def set_type
    self.type = self.class.name
  end
end

Check it works

bin/rails c

Animal::Cat.create name: 'Meow'
# => #<Animal::Cat id: 1, name: "Meow", type: "Animal::Cat", created_at: "2016-06-09 17:51:51", updated_at: "2016-06-09 17:51:51">

Animal::Dog.create name: 'Woof'
# => #<Animal::Dog id: 2, name: "Woof", type: "Animal::Dog", created_at: "2016-06-09 17:51:54", updated_at: "2016-06-09 17:51:54">

Animal.create
# => ArgumentError: 'Animal' is not a valid type

Animal.first
# => #<Animal::Cat id: 1, name: "Meow", type: "Animal::Cat", created_at: "2016-06-09 17:51:51", updated_at: "2016-06-09 17:51:51">