[Rails]enum定義のあれやこれ

$ rails new enum_app

$ cd enum_app

$ rails g model user name:string email:string role:integer

class CreateUsers < ActiveRecord::Migration[6.1]
  def change
    create_table :users do |t|
      t.string :name, null: false
      t.string :email, null: false
      t.integer :role, null: false, default: 0

      t.timestamps
    end
    add_index :users, :email, unique: true
  end
end

$ rails db:migrate

class User < ApplicationRecord

  #　省略

  enum role: {
    general: 0, author: 1,
    editor: 2, admin: 10
  }

end

$ rails c
irb(main):001:0> user = User.new(name: 'sample1', email: 'sample1@example.com', role: 0)
   (1.2ms)  SELECT sqlite_version(*)
=> #<IntUser id: nil, name: "sample1", email: "sample1@example.com", role: "general", created_at: nil, updated_at: nil>
irb(main):002:0> user.save
  TRANSACTION (0.1ms)  begin transaction
  User Exists? (0.8ms)  SELECT 1 AS one FROM "users" WHERE "users"."email" = ? LIMIT ?  [["email", "sample1@example.com"], ["LIMIT", 1]]
  User Create (1.9ms)  INSERT INTO "users" ("name", "email", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["name", "sample1"], ["email", "sample1@example.com"], ["created_at", "2021-11-18 06:57:18.111615"], ["updated_at", "2021-11-18 06:57:18.111615"]]
  TRANSACTION (1.3ms)  commit transaction
=> true
irb(main):003:0> user
=> #<User id: 4, name: "sample1", email: "sample1@example.com", role: "general", created_at: "2021-11-18 06:57:18.111615000 +0000", updated_at: "2021-11-18 06:57:18.111615000 +0000">
irb(main):004:0> user.role
=> "general"

irb(main):004:0> user = a
=> #<IntUser id: 1, name: "sample1", email: "sample1@example.com", role: "general", created_at: "2021-12-06 00:46:18.782945000 +0000", updated_at: "2021-12-06 00:46:18.782945000 +0000">
irb(main):005:0> user.general?
=> true

irb(main):004:0> user.admin!
  TRANSACTION (0.2ms)  begin transaction
  User Exists? (0.3ms)  SELECT 1 AS one FROM "users" WHERE "users"."email" = ? AND "users"."id" != ? LIMIT ?  [["email", "sample1@example.com"], ["id", 5], ["LIMIT", 1]]
  User Update (2.7ms)  UPDATE "users" SET "role" = ?, "updated_at" = ? WHERE "users"."id" = ?  [["role", 10], ["updated_at", "2021-12-06 00:26:57.367025"], ["id", 5]]
  TRANSACTION (2.7ms)  commit transaction
=> true
irb(main):005:0> user
=> #<User id: 5, name: "sample1", email: "sample1@example.com", role: "admin", created_at: "2021-12-06 00:26:37.446213000 +0000", updated_at: "2021-12-06 00:26:57.367025000 +0000">

irb(main):006:0> User.roles
=> {"general"=>0, "author"=>1, "editor"=>2, "admin"=>10}