Simple enum-like field support for ActiveRecord (including validations and i18n)
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SimpleEnum - unobtrusive enum-like fields for ActiveRecord

A Rails plugin which brings easy-to-use enum-like functionality to ActiveRecord and Mongoid models (now compatible with rails 3.1, ruby 1.9 and jruby).

Since version 1.4, simple_enum is no longer compatible with activerecord 2.x, use version 1.3.2 instead: <>.

For Mongoid support, you need to use the master branch as of Jan 28, 2012 as earlier branches do not give you SimpleEnum::Mongoid. Also, you need to include this gem after you include Mongoid in GemFile. Otherwise, code for supporting Mongoid will not run.

Note: a recent search on github for `enum` turned out, that there are many, many similar solutions.

ActiveRecord Quick start

Add this to a model:

class User < ActiveRecord::Base
  as_enum :gender, :female => 1, :male => 0

Then create the required `gender_cd` column using migrations:

class AddGenderColumnToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :gender_cd, :integer

  def self.down
    remove_column :users, :gender_cd

Mongoid Quick start

Add this to a model:

class User
  include Mongoid::Document
  include SimpleEnum::Mongoid

  as_enum :gender, :female => 1, :male => 0

Working with enums

Done. Now it's possible to pull some neat tricks on the new column, yet the original db column (gender_cd) is still intact and not touched by any fancy metaclass or similar.

jane =
jane.gender = :female
jane.female?   # => true
jane.male?     # => false
jane.gender    # => :female
jane.gender_cd # => 1

Easily switch to another value using the bang methods.

joe =
joe.male!     # => :male
joe.gender    # => :male
joe.gender_cd # => 0

There are even some neat tricks at class level, which might be useful when creating queries, displaying option elements or similar:

User.genders            # => { :male => 0, :female => 1 }
User.genders(:male)     # => 0, same as User.male
User.female             # => 1
User.genders.female     # => 1, same as User.female or User.genders(:female)

Wait, there's more!

  • Too tired of always adding the integer values? Try:

    class User < ActiveRecord::Base
      as_enum :status, [:deleted, :active, :disabled] # translates to :deleted => 0, :active => 1, :disabled => 2

    Disclaimer: if you ever decide to reorder this array, beaware that any previous mapping is lost. So it's recommended to create mappings (that might change) using hashes instead of arrays. For stuff like gender it might be probably perfectly fine to use arrays though.

  • Want to use `SimpleEnum` in an ActiveModel, or other class, just do:

    class MyModel
      include SimpleEnum
      attr_accessor :gender_cd
      as_enum :gender, [:male, :female]
  • Maybe you've columns named differently than the proposed {column}_cd naming scheme, feel free to use any column name by providing an option:

    class User < ActiveRecord::Base
      as_enum :gender, [:male, :female], :column => 'sex'
  • Need to provide custom options for the mongoid field, or skip the automatically generated field?

    # skip field generation
    field :gender_cd # <- create field manually (!)
    as_enum :gender, [:male, :female], :field => false
    # custom field options (directly passed to Mongoid::Document#field)
    as_enum :gender, [:male, :female], :field => { :type => Integer, :default => 1 }
  • To make it easier to create dropdowns with values use:

    <%= select(:user, :gender, User.genders.keys) %>
  • It's possible to validate the internal enum values, just like any other ActiveRecord validation:

    class User < ActiveRecord::Base
      as_enum :gender, [:male, :female]
      validates_as_enum :gender

    All common options like :if, :unless, :allow_nil and :message are supported, because it just works within the standard validates_each-loop. This validation method does not check the value of user.gender, but instead the value of @user.gender_cd.

  • If the shortcut methods (like <symbol>?, <symbol>! or Klass.<symbol>) conflict with something in your class, it's possible to define a prefix:

    class User < ActiveRecord::Base
      as_enum :gender, [:male, :female], :prefix => true
    jane = :gender => :female
    jane.gender_female? # => true
    User.gender_female  # => 1, this also works on the class methods

    The :prefix option not only takes a boolean value as an argument, but instead can also be supplied a custom prefix (i.e. any string or symbol), so with :prefix => 'foo' all shortcut methods would look like: foo_<symbol>... Note: if the :slim => true is defined, this option has no effect whatsoever (because no shortcut methods are generated).

  • Sometimes it might be useful to disable the generation of the shortcut methods (<symbol>?, <symbol>! and Klass.<symbol>), to do so just add the option :slim => true:

    class User < ActiveRecord::Base
      as_enum :gender, [:male, :female], :slim => true
    jane = :gender => :female
    jane.female? # => throws NoMethodError: undefined method `female?'
    User.male    # => throws NoMethodError: undefined method `male'

    Yet the setter and getter for gender, as well as the User.genders methods are still available, only all shortcut methods for each of the enumeration values are not generated.

    It's also possible to set :slim => :class which only disables the generation of any class-level shortcut method, because those are also available via the enhanced enumeration hash:

    class Message < ActiveRecord::Base
      as_enum :status, { :unread => 0, :read => 1, :archived => 99 }, :slim => :class
    msg = :body => 'Hello World!', status_cd => 0                      # => false; shortuct methods on instance are still enabled
    msg.status                     # => :unread
    Message.unread                 # => throws NoMethodError: undefined method `unread`
    Message.statuses.unread        # => 0
    Message.statuses.unread(true)  # => :unread
    # or useful for IN queries
    Messages.statuses(:unread, :read) # => [0, 1]
  • As a default an ArgumentError is raised if the user tries to set the field to an invalid enumeration value, to change this behaviour use the :whiny option:

    class User < ActiveRecord::Base
      as_enum :gender, [:male, :female], :whiny => false
  • Need translated keys et al in your forms? SimpleEnum provides a <enum>_for_select method:

    # on the gender field
    <%= select("user", "gender", User.genders_for_select) %>
    # or on the '_cd' field
    <%= select("user", "gender_cd", User.genders_for_select(:value))

    Translations need to be stored like:

          user:              # the Model, as
            genders:         # pluralized version of :gender
              male: männlich
              female: weiblich
  • To define any option globally, like setting :whiny to false, or globally enable :prefix; all default options are stored in SimpleEnum.default_options, this hash can be easily changed in your initializers or wherever:

    # e.g. setting :prefix => true (globally)
    SimpleEnum.default_options[:prefix] = true

Best practices

Do not use the same name for the enum as for the column, note that this mode of use is deprecated starting with version 1.4.1, e.g.

as_enum :status, [:active, :inactive, :archived], :column => "status"

as_enum :project_status, [:active, :inactive, :archived], :column => "status"

Do not use states named after existing, or well known method names, like `new` or `create`, e.g.

# BAD, conflicts with Rails ActiveRecord Methods (!)
as_enum :handle, [:new, :create, :update]

# BETTER, prefixes all methods
as_enum :handle, [:new, :create, :update], :prefix => true

Searching for certain values by using the finder methods:

User.where(:gender_cd => User.female)

Working with database backed values, now assuming that there exists a genders table:

class Person < ActiveRecord::Base
  as_enum :gender, { |g| [,] } # map to array of symbols

Working with object backed values, the only requirement to enable this is that a) either a field name name exists or b) a custom method to convert an object to a symbolized form named to_enum_sym (for general uses overriding to_enum is perfectly fine) exists:

class Status < ActiveRecord::Base
  # this has a column named :name
  STATUSES = self.order(:name)

class BankTransaction < ActiveRecord::Base
  as_enum :status, Status::STATUSES

# what happens now? the id's of Status now serve as enumeration key and the
# Status object as the value so...
t =
t.status # => #<Status id: 1, name: "pending">

# and it's also possible to access the objects/values using:
BankTransaction.statuses(:pending) # => 1, access by symbol (not) the object!
BankTransaction.statuses.pending   # => 1
BankTransaction.statuses.pending(true) # => #<Status id: 1, name: "pending">

Known issues/Open items

  • Maybe the :whiny option should default to false, so that generally no exceptions are thrown if a user fakes a request?

  • Clean-up code and tests -> bring down LOC ;) (but maintain Code LOC vs. Test LOC ratio which is currently 1:2.9)

  • Make `:slim => true` the default option…?


  • @dmitry - bugfixes and other improvements

  • @tarsolya - implemented all the ruby 1.9 and rails 3 goodness!

  • @dbalatero - rails 2.3.5 bugfix & validator fixes

  • @johnthethird - feature for _for_select to return the values

  • @sinsiliux - ruby 1.9 fixes and removed AR dependency

Licence & Copyright

Copyright © 2011 by Lukas Westermann, Licenced under MIT Licence (see LICENCE file)