Added ActiveRecord::Base#enum for declaring enum attributes where the values...

Added ActiveRecord::Base#enum for declaring enum attributes where the values map to integers in the database, but can be queried by name

activerecord/CHANGELOG.md

+*  Added ActiveRecord::Base#enum for declaring enum attributes where the values map to integers in the database, but can be queried by name. 
+
+   Example:
+    	class Conversation < ActiveRecord::Base
+    	  enum status: %i( active archived )
+    	end
+    	
+    	Conversation::STATUS # => { active: 0, archived: 1 }
+    	
+    	# conversation.update! status: 0
+    	conversation.active!
+    	conversation.active? # => true
+    	conversation.status  # => :active
+    	
+    	# conversation.update! status: 1
+    	conversation.archived!
+    	conversation.archived? # => true
+    	conversation.status    # => :archived
+    	
+    	# conversation.update! status: 1
+    	conversation.status = :archived
+
+	*DHH*
+
+
 *   ActiveRecord::Base#attribute_for_inspect now truncates long arrays (more than 10 elements)
 
     *Jan Bernacki*

activerecord/lib/active_record.rb

@@ -37,6 +37,7 @@ module ActiveRecord
   autoload :ConnectionHandling
   autoload :CounterCache
   autoload :DynamicMatchers
+  autoload :Enum
   autoload :Explain
   autoload :Inheritance
   autoload :Integration

activerecord/lib/active_record/base.rb

@@ -291,6 +291,7 @@ class Base
     extend Translation
     extend DynamicMatchers
     extend Explain
+    extend Enum
     extend Delegation::DelegateCache
 
     include Persistence

activerecord/lib/active_record/enum.rb

+module ActiveRecord
+  # Declare an enum attribute where the values map to integers in the database, but can be queried by name. Example:
+  #
+  #   class Conversation < ActiveRecord::Base
+  #     enum status: %i( active archived )
+  #   end
+  #
+  #   Conversation::STATUS # => { active: 0, archived: 1 }
+  #
+  #   # conversation.update! status: 0
+  #   conversation.active!
+  #   conversation.active? # => true
+  #   conversation.status  # => :active
+  #   
+  #   # conversation.update! status: 1
+  #   conversation.archived!
+  #   conversation.archived? # => true
+  #   conversation.status    # => :archived
+  #   
+  #   # conversation.update! status: 1
+  #   conversation.status = :archived
+  #
+  # You can set the default value from the database declaration, like:
+  #
+  #   create_table :conversation do
+  #     t.column :status, :integer, default: 0
+  #   end
+  # 
+  # Good practice is to let the first declared status be the default.
+  module Enum
+    def enum(definitions)
+      definitions.each do |name, values|
+        const_name = name.to_s.upcase
+
+        # DIRECTION = { }
+        const_set const_name, {}
+
+        # def direction=(value) self[:direction] = DIRECTION[value] end
+        class_eval "def #{name}=(value) self[:#{name}] = #{const_name}[value] end"
+
+        # def direction() DIRECTION.key self[:direction] end
+        class_eval "def #{name}() #{const_name}.key self[:#{name}] end"
+
+        values.each_with_index do |value, i|
+          # DIRECTION[:incoming] = 0
+          const_get(const_name)[value] = i
+
+          # scope :incoming, -> { where direction: 0 }
+          scope value, -> { where name => i }
+
+          # def incoming?() direction == 0 end
+          class_eval "def #{value}?() self[:#{name}] == #{i} end"
+
+          # def incoming! update! direction: :incoming end
+          class_eval "def #{value}!() update! #{name}: :#{value} end"
+        end
+      end
+    end
+  end
+end

activerecord/test/cases/enum_test.rb

+require 'cases/helper'
+require 'models/book'
+
+class StoreTest < ActiveRecord::TestCase
+  fixtures :books
+
+  setup do
+    @book = Book.create! name: 'REMOTE'
+  end
+
+  test "query state by predicate" do
+    assert @book.proposed?
+    assert_not @book.written?
+    assert_not @book.published?
+  end
+  
+  test "query state with symbol" do
+    assert_equal :proposed, @book.status
+  end
+
+  test "update by declaration" do
+    @book.written!
+    assert @book.written?
+  end
+  
+  test "update by setter" do
+    @book.update! status: :written
+    assert @book.written?
+  end
+  
+  test "constant" do
+    assert_equal 0, Book::STATUS[:proposed]
+    assert_equal 1, Book::STATUS[:written]
+    assert_equal 2, Book::STATUS[:published]
+  end
+end

activerecord/test/models/book.rb

@@ -2,8 +2,10 @@ class Book < ActiveRecord::Base
   has_many :authors
 
   has_many :citations, :foreign_key => 'book1_id'
-  has_many :references, -> { distinct }, :through => :citations, :source => :reference_of
+  has_many :references, -> { distinct }, through: :citations, source: :reference_of
 
   has_many :subscriptions
-  has_many :subscribers, :through => :subscriptions
+  has_many :subscribers, through: :subscriptions
+  
+  enum status: %i( proposed written published )
 end

activerecord/test/schema/schema.rb

@@ -94,6 +94,7 @@ def create_table(*args, &block)
   create_table :books, :force => true do |t|
     t.integer :author_id
     t.column :name, :string
+    t.column :status, :integer, default: 0
   end
 
   create_table :booleans, :force => true do |t|