= EnumerateIt - Ruby Enumerations

Author: Cássio Marques - cassiommc at gmail

== Description

Ok, I know there are a lot of different solutions to this problem. But none of them solved my problem,
so here's EnumerateIt. I needed to build a Rails application around a legacy database and this database was
filled with those small, unchangeable tables used to create foreign key constraints everywhere.

=== For example:

   Table "public.relationshipstatus"
  Column     |     Type      | Modifiers
  -------------+---------------+-----------
   code        | character(1)  | not null
   description | character(11) |
  Indexes:
    "relationshipstatus_pkey" PRIMARY KEY, btree (code)

  select * from relationshipstatus;
  code   |  description
  -------+--------------
  1      | Single
  2      | Married
  3      | Widow
  4      | Divorced


And then I had things like a people table with a 'relationship_status' column with a foreign key
pointing to the relationshipstatus table.

While this is a good thing from the database normalization perspective, managing this values in
my tests was very hard. Doing database joins just to get the description of some value was absurd.
And, more than this, referencing them in my code using magic numbers was terrible and meaningless:
What does it mean when we say that someone or something is '2'?

Enter EnumerateIt.

== Creating enumerations

Enumerations are created as models, but you can put then anywhere in your application. In Rails
applications, you can put them inside models/.

   class RelationshipStatus < EnumerateIt::Base
     associate_values(
       :single   => [1, 'Single'],
       :married  => [2, 'Married'],
       :widow    => [3, 'Widow'],
       :divorced => [4, 'Divorced']
     )
   end

This will create some nice stuff:

* Each enumeration's value will turn into a constant:

   RelationshipStatus::SINGLE # returns 1
   RelationshipStatus::MARRIED # returns 2 and so on...

* You can retrieve a list with all the enumeration codes:

   RelationshipStatus.list # [1,2,3,4]

* You can get an array of options, ready to use with the 'select', 'select_tag', etc family of Rails helpers.

   RelationshipStatus.to_a # [["Divorced", 4],["Married", 2],["Single", 1],["Widow", 3]]

* You can retrieve a list with values for a group of enumeration constants.

   RelationshipStatus.values_for %w(MARRIED SINGLE) # [2, 1]

* You can retrieve the value for a specific enumeration constant:

   RelationshipStatus.value_for("MARRIED") # 2

* You can retrieve the symbol used to declare a specific enumeration value:

   RelationshipStatus.key_for(RelationshioStatus::MARRIED) # :married

* You can manipulate the hash used to create the enumeration:

   RelationshipStatus.enumeration # returns the exact hash used to define the enumeration

You can also create enumerations in the following ways:

* Passing an array of symbols, so that the respective value for each symbol will be the stringified version of the symbol itself:

   class RelationshipStatus < EnumerateIt::Base
     associate_values :married, :single
   end

   RelationshipStatus::MARRIED # returns "married" and so on

* Passing hashes where the value for each key/pair does not include a translation. In this case, the I18n feature will be used (more on this below):

   class RelationshipStatus < EnumerateIt::Base
     associate_values :married => 1, :single => 2
   end


== Using enumerations

The cool part is that you can use these enumerations with any class, be it an ActiveRecord instance
or not.

   class Person
     include EnumerateIt
     attr_accessor :relationship_status

     has_enumeration_for :relationship_status, :with => RelationshipStatus
   end

The :with option is not required. If you ommit it, EnumerateIt will try to load an enumeration class based on the camelized attribute name.

This will create:

* A humanized description for the values of the enumerated attribute:

   p = Person.new
   p.relationship_status = RelationshipStatus::DIVORCED
   p.relationsip_status_humanize # => 'Divorced'

* If you don't supply a humanized string to represent an option, EnumerateIt will use a 'humanized' version of the hash's key to humanize the attribute's value:

   class RelationshipStatus < EnumerateIt::Base
     associate_values(
       :married => 1,
       :single => 2
     )
   end

   p = Person.new
   p.relationship_status = RelationshipStatus::MARRIED
   p.relationship_status_humanize # => 'Married'

* The associated enumerations can be retrieved with the 'enumerations' class method.

   Person.enumerations[:relationship_status] # => RelationshipStatus

* If you pass the :create_helpers option as 'true', it will create a helper method for each enumeration option (this option defaults to false):

   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => RelationshipStatus, :create_helpers => true
   end

   p = Person.new
   p.relationship_status = RelationshipStatus::MARRIED
   p.married? #=> true
   p.divorced? #=> false

* The :create_helpers also creates some mutator helper methods, that can be used to change the attribute's value.

   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => RelationshipStatus, :create_helpers => true
   end

   p = Person.new
   p.married!
   p.married? #=> true
   p.divorced? #=> false

* If you pass the :create_scopes option as 'true', it will create a scope method for each enumeration option (this option defaults to false):

   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => RelationshipStatus, :create_scopes => true
   end

   Person.married.to_sql # => SELECT "people".* FROM "people" WHERE "people"."relationship_status" = 1

NOTE: The :create_scopes option can only be used for Rails.version >= 3.0.0. 

* If your class can manage validations and responds to :validates_inclusion_of, it will create this validation:

   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => RelationshipStatus
   end

   p = Person.new :relationship_status => 6 # => there is no '6' value in the enumeration
   p.valid? # => false
   p.errors[:relationship_status] # => "is not included in the list"

* If your class can manage validations and responds to :validates_presence_of, you can pass the :required options as true and this validation will be created for you (this option defaults to false):

   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :required => true
   end

   p = Person.new :relationship_status => nil
   p.valid? # => false
   p.errors[:relationship_status] # => "can't be blank"


Remember that in Rails 3 you can add validations to any kind of class and not only to those derived from
ActiveRecord::Base.

== I18n

I18n lookup is provided on both '_humanized' and 'Enumeration#to_a' methods, given the hash key is a Symbol. The I18n strings are
located on enumerations.'enumeration_name'.'key' :

  class RelationshipStatus < EnumerateIt::Base
   associate_values(
     :married => 1,
     :single => 2,
     :divorced => [3, 'He's divorced']
   )
  end

  # your locale file
  pt:
    enumerations:
      relationship_status:
        married: Casado

  p = Person.new
  p.relationship_status = RelationshipStatus::MARRIED
  p.relationship_status_humanize # => 'Casado'

  p.relationship_status = RelationshipStatus::SINGLE
  p.relationship_status_humanize # => 'Single' => nonexistent key

  p.relationship_status = RelationshipStatus::DIVORCED
  p.relationship_status_humanize # => 'He's divorced' => uses the provided string

You can also translate specific values:

  RelationshipStatis.t(1) # => 'Casado'

== Installation

  gem install enumerate_it

== Using with Rails

* Create an initializer with the following code:

  ActiveRecord::Base.send :include, EnumerateIt

* Add the 'enumerate_it' gem as a dependency in your environment.rb (Rails 2.3.x) or Gemfile (if you're using Bundler)

An interesting approach to use it in Rails apps is to create an app/enumerations folder and add it to your autoload path in config/application.rb:

  module YourApp
    class Application < Rails::Application
      config.autoload_paths << "#{Rails.root}/app/enumerations"
    end
  end

There is also a Rails Generator that you can use to generate enumerations and their locale files. Take a look at how to use it running 

  rails generate enumerate_it --help

== Ruby 1.9

EnumerateIt is fully compatible with Ruby 1.9.1 and 1.9.2 (all tests pass)

* Note: on ruby 1.9.2, if you are using the enumerations in a separate folder like app/models/enumerations, and have to use the :with parameter, you have to clear the enum class namespace to a global scope by using ::EnumClass instead of EnumClass:

   # 1.8.7
   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => EnumClass
   end

   # 1.9.2
   class Person < ActiveRecord::Base
     has_enumeration_for :relationship_status, :with => ::EnumClass
   end


== Why did you reinvent the wheel?

There are other similar solutions to the problem out there, but I could not find one that
worked both with strings and integers as the enumerations' codes. I had both situations in
my legacy database.

== Why defining enumerations outside the class that use it?

* I think it's cleaner.
* You can add behaviour to the enumeration class.
* You can reuse the enumeration inside other classes.

== Note on Patches/Pull Requests

* Fork the project.
* Make your feature addition or bug fix.
* Add tests for it. This is important so I don't break it in a
  future version unintentionally.
* Commit, do not mess with rakefile, version, or history.
  (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
* Send me a pull request. Bonus points for topic branches.

== Copyright

Copyright (c) 2010 Cássio Marques. See LICENSE for details.