Other good posts on the topic:

Enums are a Rails feature, not a Ruby feature.

  • good - we get validations for available options, can fire actions and scopes
  • bad - not so cool to use integer to represent strings

Option 1 # 

# app/models/post.rb
  enum status: %i[draft reviewed published]

# migration
  add_column :posts, :status, :integer, default: 0

inclusion validation works automatically with enums! # 

# app/models/post.rb
  # this is automatic!!!
  validates :status, inclusion: { in: Post.statuses.keys }

In this case, the order of enums is very important:

0 = draft 1 = reviewed 2 = published

If we add new values - add at the end of the array!

to get keys/values # 

Post.statuses.keys
=> ["draft", "published"] 
Post.statuses.values
=> [0, 1]

to select an enum in a form # 

# basic
<%= form.select :status, Post.statuses.keys %>
# advanced
<%= form.select :status, options_for_select(Post.statuses.keys, { selected: @post.status || Post.new.status }), include_blank: true %>

Option 2 - fix integer values to specific strings (better) # 

# app/models/post.rb
  enum status: { draft: 2, reviewed: 1, published: 0 }

Option 3 - map enum to strings (the best) # 

# app/models/post.rb
  enum status: {
    draft: "draft",
    reviewed: "reviewed",
    published: "published"
  }

# migration
  add_column :posts, :status, :string

Postgresql enum #

Rails 7 now supports postgresql enum migrations:

# migration
class CreatePosts < ActiveRecord::Migration[7.0]
  def up
    create_enum :post_status, ["draft", "reviewed", "published"]

    create_table :posts do |t|
      t.enum :status, enum_type: "post_status", default: "draft", null: false
      # t.column :status, :post_status, null: false, index: true
    end
  end

  # to drop the enum table:
  def down
    remove_column :posts, :status

    execute <<-SQL
      DROP TYPE post_status;
    SQL
  end
end

Bonus: setting default values #

instead of setting defaults on database level like:

# migration
  add_column :posts, :status, :string, default: 'draft'
  add_column :posts, :category, :string, default: 'Rails'

you could (better) do it in the model:

# app/models/post.rb
  enum status: %i[draft reviewed published], _default: 'draft'
  enum category: { rails: 'Rails', ruby: 'Ruby' }, _default: 'Rails'

to get the default value:

Post.new.status # => "draft"

a few methods that can be called when using enums: # 

Post::STATUSES[:draft] # => "draft"

post.draft! # => true
post.draft? # => true
post.status # => "draft"

post.reviewed! # => true
post.draft?    # => false
post.status    # => "reviewed"
post.reviewed? # => true

Post.draft     # => Collection of all Posts in draft status
Post.not_draft     # => Collection of all Posts NOT in draft status
Post.reviewed  # => Collection of all Posts in reviewed status
Post.published # => Collection of all Posts in published status