Make enum feature work with dirty methods

To make this possible we have to override the save_changed_attribute
hook.

3 files changed, 76 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 170818cd1c..9de076961b 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,21 @@
+*   Make enum fields work as expected with the `ActiveModel::Dirty` API.
+
+    Before this change, using the dirty API would have surprising results:
+
+        conversation = Conversation.new
+        conversation.status = :active
+        conversation.status = :archived
+        conversation.status_was # => 0
+
+    After this change, the same code would result in:
+
+        conversation = Conversation.new
+        conversation.status = :active
+        conversation.status = :archived
+        conversation.status_was # => "active"
+
+    *Rafael Mendonça França*
+
 *   Ensure `second` through `fifth` methods act like the `first` finder.
 
     The famous ordinal Array instance methods defined in ActiveSupport
diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 3deb2d65f8..06e87cf854 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -63,6 +63,12 @@ module ActiveRecord
   #
   #   Conversation.where("status <> ?", Conversation.statuses[:archived])
   module Enum
+    DEFINED_ENUMS = [] # :nodoc:
+
+    def enum_attribute?(attr_name) # :nodoc:
+      DEFINED_ENUMS.include?(attr_name.to_sym)
+    end
+
     def enum(definitions)
       klass = self
       definitions.each do |name, values|
@@ -70,6 +76,8 @@ module ActiveRecord
         enum_values = ActiveSupport::HashWithIndifferentAccess.new
         name        = name.to_sym
 
+        DEFINED_ENUMS.unshift name
+
         # def self.statuses statuses end
         klass.singleton_class.send(:define_method, name.to_s.pluralize) { enum_values }
 
@@ -114,7 +122,16 @@ module ActiveRecord
     private
       def _enum_methods_module
         @_enum_methods_module ||= begin
-          mod = Module.new
+          mod = Module.new do
+            def save_changed_attribute(attr_name, value)
+              if self.class.enum_attribute?(attr_name)
+                old = clone_attribute_value(:read_attribute, attr_name)
+                changed_attributes[attr_name] = self.class.public_send(attr_name.pluralize).key old
+              else
+                super
+              end
+            end
+          end
           include mod
           mod
         end
diff --git a/activerecord/test/cases/enum_test.rb b/activerecord/test/cases/enum_test.rb
index 1f98801e93..0fe7dfe4ea 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -51,6 +51,46 @@ class EnumTest < ActiveRecord::TestCase
     assert @book.written?
   end
 
+  test "enum changed attributes" do
+    old_status = @book.status
+    @book.status = :published
+    assert_equal old_status, @book.changed_attributes[:status]
+  end
+
+  test "enum changes" do
+    old_status = @book.status
+    @book.status = :published
+    assert_equal [old_status, 'published'], @book.changes[:status]
+  end
+
+  test "enum attribute was" do
+    old_status = @book.status
+    @book.status = :published
+    assert_equal old_status, @book.attribute_was(:status)
+  end
+
+  test "enum attribute changed" do
+    @book.status = :published
+    assert @book.attribute_changed?(:status)
+  end
+
+  test "enum attribute changed to" do
+    @book.status = :published
+    assert @book.attribute_changed?(:status, to: 'published')
+  end
+
+  test "enum attribute changed from" do
+    old_status = @book.status
+    @book.status = :published
+    assert @book.attribute_changed?(:status, from: old_status)
+  end
+
+  test "enum attribute changed from old status to new status" do
+    old_status = @book.status
+    @book.status = :published
+    assert @book.attribute_changed?(:status, from: old_status, to: 'published')
+  end
+
   test "assign non existing value raises an error" do
     e = assert_raises(ArgumentError) do
       @book.status = :unknown