ClassyEnum

ClassyEnum is a Ruby on Rails gem that adds class-based enumerator functionality to Active Record attributes.

This README is also available in a user-friendly DocumentUp format.

Rails & Ruby Versions Supported

Rails: 3.2.x - 4.2.x

Ruby: 1.9.3, 2.0.0, 2.1.x, 2.2.x, and 2.3.x

Installation

The gem is hosted at rubygems.org

Despite RailsGuides claiming that all directories under app will be autoloaded, I've had reports of this not being the case with newer versions of Ruby and Rails.

You may need to add the enums path to config/application.rb:

# Make sure classy_enum enums get loaded
config.autoload_paths += %W(#{config.root}/app/enums)

Upgrading?

See the wiki for notes about upgrading from previous versions.

Getting Started & Example Usage

The most common use for ClassyEnum is to replace database lookup tables where the content and behavior is mostly static and has multiple "types". Please see the Wiki for a short discussion on use cases comparing ClassyEnum to other gems.

In this example, I have an Active Record model called Alarm with an attribute called priority. Priority is stored as a string (VARCHAR) type in the database and is converted to an enum value when requested.

1. Generate the Enum

The fastest way to get up and running with ClassyEnum is to use the built-in Rails generator like so:

rails generate classy_enum Priority low medium high

NOTE: You may destroy/revoke an enum by using the rails destroy command:

rails destroy classy_enum Priority

A new enum template file will be created at app/enums/priority.rb that will look like:

class Priority < ClassyEnum::Base
end

class Priority::Low < Priority
end

class Priority::Medium < Priority
end

class Priority::High < Priority
end

NOTE: The class order is important because it defines the enum member ordering as well as additional ClassyEnum behavior described below.

2. Customize the Enum

The generator creates a default setup, but each enum member can be changed to fit your needs.

I have defined three priority levels: low, medium, and high. Each priority level can have different properties and methods associated with it.

I would like to add a method called #send_email? that all member subclasses respond to. By default this method will return false, but will be overridden for high priority alarms to return true.

class Priority < ClassyEnum::Base
  def send_email?
    false
  end
end

class Priority::Low < Priority
end

class Priority::Medium < Priority
end

class Priority::High < Priority
  def send_email?
    true
  end
end

3. Setup the Active Record model

My Active Record Alarm model needs a text field that will store a string representing the enum member. An example model schema might look something like:

create_table "alarms", force: true do |t|
  t.string   "priority"
  t.boolean  "enabled"
end

NOTE: Alternatively, you may use an enum type if your database supports it. See this issue for more information.

Then in my model I've included ClassyEnum::ActiveRecord and added a line that calls classy_enum_attr with a single argument representing the enum I want to associate with my model. I am also delegating the #send_email? method to my Priority enum class.

class Alarm < ActiveRecord::Base
  include ClassyEnum::ActiveRecord

  classy_enum_attr :priority

  delegate :send_email?, to: :priority
end

With this setup, I can now do the following:

@alarm = Alarm.create(priority: :medium)

@alarm.priority  # => Priority::Medium
@alarm.priority.medium? # => true
@alarm.priority.high? # => false
@alarm.priority.to_s # => 'medium'

# Should this alarm send an email?
@alarm.send_email? # => false
@alarm.priority = :high
@alarm.send_email? # => true

The enum field works like any other model attribute. It can be mass-assigned using #update_attributes.

What if your enum class name is not the same as your model's attribute name?

Just provide an optional class_name argument to declare the enum's class name. In this case, the model's attribute is called alarm_priority.

class Alarm < ActiveRecord::Base
  include ClassyEnum::ActiveRecord

  classy_enum_attr :alarm_priority, class_name: 'Priority'
end

@alarm = Alarm.create(alarm_priority: :medium)
@alarm.alarm_priority  # => Priority::Medium

Internationalization

ClassyEnum provides built-in support for translations using Ruby's I18n library. The translated values are provided via a #text method on each enum object. Translations are automatically applied when a key is found at locale.classy_enum.enum_parent_class.enum_value, or a default value is used that is equivalent to #to_s.titleize.

Given the following file config/locales/es.yml

es:
  classy_enum:
    priority:
      low: 'Bajo'
      medium: 'Medio'
      high: 'Alto'

You can now do the following:

@alarm.priority = :low
@alarm.priority.text # => 'Low'

I18n.locale = :es

@alarm.priority.text # => 'Bajo'

Using Enum as a Collection

ClassyEnum::Base extends the Enumerable module which provides several traversal and searching methods. This can be useful for situations where you are working with the collection, as opposed to the attributes on an Active Record object.

# Find the priority based on string or symbol:
Priority.find(:low) # => Priority::Low.new
Priority.find('medium') # => Priority::Medium.new

# Test if a priority is valid:
Priority.include?(:low) # => true
Priority.include?(:lower) # => false

# List priorities base strings:
Priority.map { |p| p.to_s } # => ["low", "medium", "high"]

# Find the lowest priority that can send email:
Priority.find(&:send_email?) # => Priority::High.new

# Find the priorities that are lower than Priority::High
Priority.select {|p| p < :high } # => [Priority::Low.new, Priority::Medium.new]

# Iterate over each priority:
Priority.each do |priority|
  puts priority.send_email?
end

Default Enum Value

As with any Active Record attribute, default values can be specified in the database table and will propagate to new instances. However, there may be times when you can't or don't want to set the default value in the database. For these occasions, a default value can be specified like so:

class Alarm < ActiveRecord::Base
  include ClassyEnum::ActiveRecord

  classy_enum_attr :priority, default: 'medium'
end

Alarm.new.priority # => Priority::Medium

You may also use a Proc object to set the default value. The enum class is yielded to the block and can be used to determine the default at runtime.

class Alarm < ActiveRecord::Base
  include ClassyEnum::ActiveRecord

  classy_enum_attr :priority, default: ->(enum){ enum.max }
end

Alarm.new.priority # => Priority::High

Back Reference to Owning Object

In some cases you may want an enum class to reference the owning object (an instance of the Active Record model). Think of it as a belongs_to relationship, where the enum belongs to the model.

By default, the back reference can be called using #owner. If you want to refer to the owner by a different name, you must explicitly declare the owner name in the classy_enum parent class using the .owner class method.

Example using the default #owner method:

class Priority < ClassyEnum::Base
end

# low and medium subclasses omitted

class Priority::High < Priority
  def send_email?
    owner.enabled?
  end
end

Example where the owner reference is explicitly declared:

class Priority < ClassyEnum::Base
  owner :alarm
end

# low and medium subclasses omitted

class Priority::High < Priority
  def send_email?
    alarm.enabled?
  end
end

In the above examples, high priority alarms are only emailed if the owning alarm is enabled.

@alarm = Alarm.create(priority: :high, enabled: true)

# Should this alarm send an email?
@alarm.send_email? # => true
@alarm.enabled = false
@alarm.send_email? # => false

Model Validation

An Active Record validator validates_inclusion_of :field, in: ENUM is automatically added to your model when you use classy_enum_attr.

If your enum only has members low, medium, and high, then the following validation behavior would be expected:

@alarm = Alarm.new(priority: :really_high)
@alarm.valid? # => false
@alarm.priority = :high
@alarm.valid? # => true

To allow nil or blank values, you can pass in :allow_nil and :allow_blank as options to classy_enum_attr:

class Alarm < ActiveRecord::Base
  include ClassyEnum::ActiveRecord

  classy_enum_attr :priority, allow_nil: true
end

@alarm = Alarm.new(priority: nil)
@alarm.valid? # => true

Active Record Querying

Classy Enum classes are plain Ruby objects, and Active Record does not know how to typecast them to strings when querying. Therefore you must explicitly convert the object to a string or symbol for the query to be valid.

Classy Enum versions before 4.0.0 supported querying directly with the enum objects. Suppport for this was removed in 4.0.0 because it depended on ARel internals, and maintaining backwards compatibility with older version of Rails was not possible.

Any of these are valid:

Alarm.where(priority: 'high')

Alarm.where(priority: Priority[:high].to_s)

Alarm.where(priority: Priority::High.new.to_s)

Note If you get an error like Cannot visit <Enum>, it means that ActiveRecord - or more accurately ARel - has received the Classy Enum class or instance directly, rather than a string representing corresponding to the database value. To resolve this issue, you need to convert the object to a string.

Form Usage

ClassyEnum includes a select_options helper method to generate an array of enum options that can be used by Rails' form builders such as SimpleForm and Formtastic.

# SimpleForm

<%= simple_form_for @alarm do |f| %>
  <%= f.input :priority, as: :select, collection: Priority.select_options %>
  <%= f.button :submit %>
<% end %>

Testing Enums

ClassyEnums can be tested by creating new instances of the ClassyEnum and testing expectations. For example:

class TestPriorityHigh < Minitest::Test
  def setup
    @priority_high_enum = Priority::High.new
  end

  def test_send_email_enabled
    assert @priority_high_enum.send_email?
  end
end

If the ClassyEnum method implementations rely upon the owner, the ClassyEnum#build method can be used with the owner option. For example:

class TestPriorityHigh < Minitest::Test
  def setup
    @alarm = Alarm.create
    @priority_high_enum = Priority::High.build(:high, owner: @alarm)
  end

  def test_send_email_enabled
    assert_equal @priority_high_enum.owner, @alarm
  end
end

Copyright

Copyright (c) 2010-2016 Peter Brown. See LICENSE for details.