spec and code to use serialized values for changes, to correctly pers…

…ist Date and DateTime fields to mongodb

lib/mongoid/dirty.rb

@@ -20,7 +20,7 @@ module Dirty #:nodoc:
     def changes
       {}.tap do |hash|
         changed.each do |name|
-          change = attribute_change(name)
+          change = [changed_attributes[name], attributes[name]] if attribute_changed?(name)
           hash[name] = change if change[0] != change[1]
         end
       end

spec/functional/mongoid/date_time_spec.rb

@@ -0,0 +1,37 @@
+require 'spec_helper'
+
+describe "Date/Time attributes" do
+
+  context "when a DateTime attribute is updated and persisted" do
+    let(:user) do
+      user = User.create! :last_login => 2.days.ago
+      user.last_login = DateTime.now
+      user
+    end
+
+    it "should be read for persistance as a UTC Time" do
+      user.changes["last_login"].last.class.should == Time
+    end
+
+    it "should persist with no exceptions thrown" do
+      user.save!
+    end
+  end
+
+  context "when a Date attribute is persisted" do
+    let(:user) do
+      user = User.create! :account_expires => 2.years.from_now
+      user.account_expires = "2/2/2002".to_date
+      user
+    end
+
+    it "should be read for persistance as a UTC Time" do
+      user.changes["account_expires"].last.class.should == Time
+    end
+
+    it "should persist with no exceptions thrown" do
+      user.save!
+    end
+  end
+
+end

spec/models/user.rb

@@ -2,6 +2,8 @@ class User
   include Mongoid::Document
 
   field :name
+  field :last_login, :type => DateTime
+  field :account_expires, :type => Date
 
   references_one :account, :foreign_key => :creator_id
   references_many :posts, :foreign_key => :author_id