ar_enum.rb

unless File.exists?('./Gemfile')
  File.write('./Gemfile', <<~GEMFILE)
    source 'http://rubygems.org'
    gem 'activerecord'
    gem 'sqlite3'
  GEMFILE
  system 'bundle install --path=vendor/bundle'
end

require 'bundler/setup'
require 'active_record'

CONFIG = {
  adapter: 'sqlite3',
  database: './ar_enum_development.sqlite3'
}.freeze
ActiveRecord::Base.configurations['ar_enum_development'] = CONFIG
ActiveRecord::Base.establish_connection(:ar_enum_development)

ActiveRecord::Schema.define do
  self.verbose = false

  create_table :users, force: true do |t|
    t.string :gender, default: 'male'
  end
end

module Encryptable
  def self.included(base)
    base.class_eval do
      around_save :encrypt_before_save_and_decrypt_after_save
    end
  end

  def encrypt_before_save_and_decrypt_after_save
    encrypt_gender
    yield
    decrypt_gender
  end

  def encrypt_gender
    v = read_attribute(:gender)
    write_attribute(:gender, v.dup.reverse) if v
  end

  def dectypt_gender
    v = read_attribute(:gender)
    write_attribute(:gender, v.dup.reverse) if v
  end
end

class User < ActiveRecord::Base
  # include Encryptable
  enum gender: { male: 'male', female: 'female', other: 'other' }
end

u1 = User.create
puts u1.male?
puts u1.gender

u2 = User.create(gender: :other)
puts u2.other?
puts u2.gender

system("sqlite3 -header -column ./ar_enum_development.sqlite3 'select * from users;'")

$ ruby ar_enum.rb
Fetching gem metadata from http://rubygems.org/..........
Fetching version metadata from http://rubygems.org/.
Resolving dependencies...
Using concurrent-ruby 1.0.5
Using i18n 0.8.1
Using minitest 5.10.1
Using thread_safe 0.3.6
Using arel 7.1.4
Using sqlite3 1.3.13
Using bundler 1.14.6
Using tzinfo 1.2.3
Using activesupport 5.0.2
Using activemodel 5.0.2
Using activerecord 5.0.2
Bundle complete! 2 Gemfile dependencies, 11 gems now installed.
Bundled gems are installed into ./vendor/bundle.
true
male
true
other
id          gender
----------  ----------
1           male
2           other

Encryptable module is a simple pseudo-encryption.
If User enables include Encryptable, it will raise ArgumentError.

$ ruby ar_enum.rb
/Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/enum.rb:139:in `assert_valid_value': 'elam' is not a valid gender (ArgumentError)
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/attribute.rb:67:in `with_value_from_user'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/attribute_set.rb:53:in `write_from_user'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/attribute_methods/write.rb:50:in `write_attribute_with_type_cast'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/attribute_methods/write.rb:32:in `write_attribute'
        from ar_enum.rb:43:in `encrypt_gender'
        from ar_enum.rb:36:in `encrypt_before_save_and_decrypt_after_save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:382:in `block in make_lambda'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:285:in `block in halting'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:447:in `block in around'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:455:in `call'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:101:in `__run_callbacks__'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activesupport-5.0.2/lib/active_support/callbacks.rb:750:in `_run_save_callbacks'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/callbacks.rb:298:in `create_or_update'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/persistence.rb:125:in `save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/validations.rb:44:in `save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/attribute_methods/dirty.rb:22:in `save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:319:in `block (2 levels) in save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:395:in `block in with_transaction_returning_status'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/connection_adapters/abstract/database_statements.rb:232:in `block in transaction'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/connection_adapters/abstract/transaction.rb:189:in `within_new_transaction'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/connection_adapters/abstract/database_statements.rb:232:in `transaction'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:211:in `transaction'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:392:in `with_transaction_returning_status'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:319:in `block in save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:334:in `rollback_active_record_state!'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/transactions.rb:318:in `save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/suppressor.rb:41:in `save'
        from /Users/kimura/work/ar_enum/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.2/lib/active_record/persistence.rb:34:in `create'
        from ar_enum.rb:57:in `<main>'