How to implement Enum Fields in your Ruby on Rails models

If you reached this page, it might be because you have searched how the hell you could create an enum field in Ruby On Rails.

Short answer: Ruby On Rails prior to version 4 does not know how to deal Enum fields, so you cannot declare enum fields. However, you can hack your model, and implement your own enum 🙂

Code your own Enum Field

Long answer: Many developers need for a reason or another to have enum fields in their database. Maybe because they need to save a status of their object, or they need something more complex. By default Rails allows you to do this by using string fields, which later you could use to fetch your information by using scopes, or custom ActiveRecord or by declaring your own methods.

Personally i needed to have some enum fields in my Ruby on Rails applications, and i have seen that i am usually repeat the same stuff all over again, thing that lead me to write the snippet at the end of this post which later allowed me to use plain vanilla Enum fields into my Database.

First is I am creating my migration or my model where i add something like this:

class CreateProducts < ActiveRecord::Migration  
  def up
    create_table :products do |t|
      t.string :name 
      t.integer :my_status_field, :limit => 1  #as a TinyInt 
      t.timestamps 
    end 
    add_index :products, :my_status_field 
  end

  def down 
    drop_table :products 
  end
end

After i am creating the needed migration and the model, we are going to implement our status column inside a model.

class Product < ActiveRecord::Base
  STATUS_ARRAY = {
    :pending             => 1,
    :open                => 2, 
    :closed              => 3, 
    :rejected            => 4, 
    :waiting_for_payment => 5 
  }

  has_enum_field :my_status_field, STATUS_ARRAY
end

By using a snippet like the one above, you can easily use this kind of syntax:

# Active Record Scopes:
pending_products = Product.pending
open_products    = Product.open
# etc

# inside an object, the following syntax

object = Product.new
object.my_status_field = :open

object.is_pending?  # => false

object.my_status_field = STATUS_ARRAY[:closed]
object.pending?    # => false
object.closed?     # => true
object.is_closed?  # => true

But, wait, there is more:

1. you have presence validators
2. you can disable the number 1 validators
3. you can disable the boolean columns
4. you can diable the scopes

We are gonna take the above product class, and we will add another hash to our customize our enum snippet, by disabling the validators and scopes.

class Product < ActiveRecord::Base
  STATUS_ARRAY = {
    :pending             => 1,
    :open                => 2,
    :closed              => 3,
    :rejected            => 4,
    :vaiting_for_payment => 5
  }

  ENUM_SETTINGS = {
    :validate => false,
    :scopes => false,
    :booleans => true
  }

  has_enum_field :my_status_field, STATUS_ARRAY, ENUM_SETTINGS
end

Before running the below example, you might want to add in your “environment.rb” or “application.rb” a require statement to include the module globbaly into your project

Finally the module:

module EnumField 
class << self
  def included(klass) 
    klass.class_eval do 
      extend ClassMethods 
      include InstanceMethods 
    end 
  end 
end

module InstanceMethods
end

module ClassMethods
  def has_enum_field(column_name, data_set, options = {:validate => true, :scopes => true, :booleans => true})
    data_set.keys.each do |ds| 
      dat = data_set[ds.to_sym]

      class_eval %{
        validates_inclusion_of :#{column_name}, :in => #{data_set}.keys  
      } if options[:validate] 

      class_eval %{
        scope :#{ds}, where('#{column_name} = ?', dat)
      } if options[:scopes] 

      class_eval %{
        def #{ds}?
          self[:#{column_name}] == #{data_set}[:#{ds}]
        end

        alias_method :is_#{ds}?, :#{ds}?
      } if options[:booleans] 

      class_eval %{
        def #{column_name}=(value)
          self[:#{column_name}] = value.is_a?(Integer) ? value : #{data_set}[value.to_sym]
        end

        def #{column_name}
          #{data_set}.key(self[:#{column_name}])
        end
      }
    end
  end
end
end

ActiveRecord::Base.send(:include, EnumField)

This module might have a problem thought, because is not 100% bullet proof. In order to achieve that, you might need to override the write_attribute method from Rails. Update:

Once with release of Rails 4, this post can be deprecated, as it has been introduced by default in Rails. Please read more on the official wiki: http://api.rubyonrails.org/v4.1.0/classes/ActiveRecord/Enum.html