GEM: iron-enum¶ ↑

Written by Rob Morris @ Irongaze Consulting LLC (irongaze.com)

Add support for rich enum values (enumerated constants) to Ruby/Rails.

Managing constants - status flags, system states, etc - is frustrating when working with Ruby and Rails. The canonical solution is to use class constants. But doing so leaves a lot to be desired. This gem provides a much more Ruby-like way of dealing with magic constants that provides symbol/key-based lookup, automatic conversion between keys and values, user-friendly naming, attribute support, model scoping and validation, and more.

To use:

# Require the gem's classes (not needed if using Bundler)
require 'iron/enum'  

# Declare an enum module.  In this case, let's say we're working on a
# shopping cart system that tracks orders.  Orders have a status - perfect
# place for an enumeration!
module OrderStatus
  enum :created,   1
  enum :cancelled, 2, 'No Sale'
  enum :purchased, 3
  enum :shipped,   4
  enum :returned,  5
end

# Once you have your enum set up, there are a host of things you can do.
# To start with, enums set up normal Ruby class constants:
>> puts OrderStatus::PURCHASED
=> 3

# But you can also refer to them with symbolic keys:
>> puts OrderStatus.value(:purchased)
=> 3

# You can convert between values, keys and text:
>> OrderStatus.value(:shipped)
=> 4
>> OrderStatus.name(:shipped)
=> 'Shipped'
>> OrderStatus.key(4)
=> :shipped

# Validate values against the set of good values
>> OrderStatus.valid_value?(10)
=> false

# Get an array of all valid values
>> OrderStatus.values
=> [1, 2, 3, 4, 5]
# Get a selection of values by key
>> OrderStatus.values(:created, :cancelled, :returned)
=> [1, 2, 5]

# This is all handy, but where enums really shine is as declared attributes
class Order < ActiveRecord::Base
  # Pass the attribute and the enum module that it uses
  enum_attr :status => OrderStatus

  # Note that if your attribute's name maps to your enum module name, you can skip the hash:
  # enum_attr :order_status
end

# Now you can set a value using a key
>> @order = Order.new
>> @order.status = :shipped
=> 4
# Test for a given value with a clear syntax
>> @order.status_returned?
=> false
# Set a value
>> @order.status_returned!
=> 5

# Setting an invalid value raises an exception
# This raises RuntimeError('Unknown key or value [27] in enum OrderStatus')
>> @order.status = 27

# You even get free scoping!
>> Order.with_status(:shipped)
=> [...all orders with status == 4...]

# And model validation, should you somehow set the field to an improper value
>> @order = Order.new
>> @order.send(:write_attribute, :status, -2)
>> @order.valid?
=> false

None, though you’ll need rspec, sqlite3 and active_record gems to test and build the gem

To install, simply run:

sudo gem install iron-enum

RVM users can skip the sudo:

gem install iron-enum

Once installed, just require it:

require 'iron-enum'