enumerate_by adds support for declaring an ActiveRecord class as an enumeration.







  • git://github.com/pluginaweek/enumerate_by.git

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Support for enumerations is dependent on the type of database you use. For example, MySQL has native support for the enum data type. However, there is no native Rails support for defining enumerations and the associations between it and other models in the application.

In addition, enumerations may often have more complex data and/or functionality associated with it that cannot simply be describe in a single column.

enumerate_by adds support for pseudo-enumerations in Rails by allowing the enumeration's records to be defined in code, but continuing to express the relationship between an enumeration and other models using ActiveRecord associations. The important thing to remember, however, is that while the associations exist, the enumerator is always used outside of the application, while either the enumerator or the enumerator's record would be referenced within the application. This means that you would reference a Color record via its enumerator (such as “red”) everywhere in the code (conditions, assigning associations, forms, etc.), but it would always be stored in the database as a true association with the integer value of 1.


class Color < ActiveRecord::Base
  enumerate_by :name

  belongs_to :group, :class_name => 'ColorGroup'
  has_many :cars

    {:id => 1, :name => 'red', :group => 'RGB'},
    {:id => 2, :name => 'blue', :group => 'RGB'},
    {:id => 3, :name => 'green', :group => 'RGB'},
    {:id => 4, :name => 'cyan', :group => 'CMYK'}

class ColorGroup < ActiveRecord::Base
  enumerate_by :name

  has_many :colors, :foreign_key => 'group_id'

    {:id => 1, :name => 'RGB'},
    {:id => 2, :name => 'CMYK'}

class Car < ActiveRecord::Base
  belongs_to :color

Each of the above models is backed by the database with its own table. Both the Color and ColorGroup enumerations automatically synchronize with the records in the database based on what's defined in their bootstrap data.

The enumerations and their associations can then be used like so:

car = Car.create(:color => 'red')   # => #<Car id: 1, color_id: 1>
car.color                           # => #<Color id: 1, name: "red">
car.color == 'red'                  # => true
car.color.name                      # => "red"

car.color = 'blue'
car.save                            # => true
car                                 # => #<Car id: 1, color_id: 2>

# Serialization
car.to_json                         # => "{id: 1, color: \"blue\"}"
car.to_xml                          # => "<car><id type=\"integer\">1</id><color>blue</color></car>"

# Lookup
Car.with_color('blue')              # => [#<Car id: 1, color_id: 2>]
car = Car.find_by_color('blue')     # => #<Car id: 1, color_id: 2>
car.color == Color['blue']          # => true

As mentioned previously, the important thing to note from the above example is that from an external perspective, “color” is simply an attribute on the Car. However, it's backed by a more complex association and model that allows Color to include advanced functionality that would normally not be possible with a simple attribute.


Before you can run any tests, the following gem must be installed:

To run against a specific version of Rails:

rake test RAILS_FRAMEWORK_ROOT=/path/to/rails


  • Rails 2.1 or later