Use Rails enum, backed by an integer column with CHECK constraint

Author: enricostano

app/models/event.rb

@@ -1,11 +1,11 @@
 class Event < ActiveRecord::Base
-  ACTIONS = ['create', 'update'].freeze
+  enum action: { created: 0, updated: 1 }
 
   belongs_to :post
   belongs_to :member
   belongs_to :transfer
 
-  validates :action, inclusion: { in: ACTIONS }, presence: true
+  validates :action, presence: true
   validate :resource_presence
 
   private

db/migrate/20180501093846_create_events.rb

@@ -9,16 +9,15 @@
 class CreateEvents < ActiveRecord::Migration
   def up
     execute <<-SQL
-      CREATE TYPE action_enum AS ENUM ('create', 'update');
-
       CREATE TABLE events (
         id          serial PRIMARY KEY,
-        action      action_enum NOT NULL,
+        action      integer NOT NULL,
         post_id     integer REFERENCES posts,
         member_id   integer REFERENCES members,
         transfer_id integer REFERENCES transfers,
         created_at  timestamp without time zone,
         updated_at  timestamp without time zone,
+        CHECK(action IN (0, 1)),
         CHECK(
           (
             (post_id IS NOT NULL)::integer +

db/schema.rb

@@ -76,8 +76,18 @@
   add_index "documents", ["documentable_id", "documentable_type"], name: "index_documents_on_documentable_id_and_documentable_type", using: :btree
   add_index "documents", ["label"], name: "index_documents_on_label", using: :btree
 
-# Could not dump table "events" because of following StandardError
-#   Unknown type 'action_enum' for column 'action'
+  create_table "events", force: :cascade do |t|
+    t.integer  "action",      null: false
+    t.integer  "post_id"
+    t.integer  "member_id"
+    t.integer  "transfer_id"
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
+  add_index "events", ["member_id"], name: "events_member_id_idx", unique: true, where: "(member_id IS NOT NULL)", using: :btree
+  add_index "events", ["post_id"], name: "events_post_id_idx", unique: true, where: "(post_id IS NOT NULL)", using: :btree
+  add_index "events", ["transfer_id"], name: "events_transfer_id_idx", unique: true, where: "(transfer_id IS NOT NULL)", using: :btree
 
   create_table "members", force: :cascade do |t|
     t.integer  "user_id"

spec/models/event_spec.rb

@@ -1,14 +1,17 @@
-require "spec_helper"
+require 'spec_helper'
 
 describe Event do
   describe 'Validations' do
     it { is_expected.to validate_presence_of(:action) }
-    it { is_expected.to validate_inclusion_of(:action).in_array(::Event::ACTIONS) }
+    it do
+      is_expected.to define_enum_for(:action)
+        .with([:created, :updated])
+    end
 
     describe '#resource_presence validation' do
       let(:post) { Fabricate(:post) }
       let(:member) { Fabricate(:member) }
-      let(:event) { Event.new action: 'create' }
+      let(:event) { Event.new action: 'created' }
 
       context 'has no resources' do
         it { expect(event).to_not be_valid }