Concernify AR AttributeMethods

10 files changed, 451 insertions, 383 deletions

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 63eb5c3eeb..b2c1c9c024 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -52,7 +52,6 @@ module ActiveRecord
   autoload :Batches, 'active_record/batches'
   autoload :Calculations, 'active_record/calculations'
   autoload :Callbacks, 'active_record/callbacks'
-  autoload :Dirty, 'active_record/dirty'
   autoload :DynamicFinderMatch, 'active_record/dynamic_finder_match'
   autoload :DynamicScopeMatch, 'active_record/dynamic_scope_match'
   autoload :Migration, 'active_record/migration'
@@ -71,6 +70,15 @@ module ActiveRecord
   autoload :Transactions, 'active_record/transactions'
   autoload :Validations, 'active_record/validations'
 
+  module AttributeMethods
+    autoload :BeforeTypeCast, 'active_record/attribute_methods/before_type_cast'
+    autoload :Dirty, 'active_record/attribute_methods/dirty'
+    autoload :Query, 'active_record/attribute_methods/query'
+    autoload :Read, 'active_record/attribute_methods/read'
+    autoload :TimeZoneConversion, 'active_record/attribute_methods/time_zone_conversion'
+    autoload :Write, 'active_record/attribute_methods/write'
+  end
+
   module Locking
     autoload :Optimistic, 'active_record/locking/optimistic'
     autoload :Pessimistic, 'active_record/locking/pessimistic'
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index ecd2d57a5a..dc42f05635 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -4,20 +4,11 @@ module ActiveRecord
   module AttributeMethods #:nodoc:
     extend ActiveSupport::Concern
 
-    DEFAULT_SUFFIXES = %w(= ? _before_type_cast)
     ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]
 
     included do
-      attribute_method_suffix(*DEFAULT_SUFFIXES)
-
       cattr_accessor :attribute_types_cached_by_default, :instance_writer => false
       self.attribute_types_cached_by_default = ATTRIBUTE_TYPES_CACHED_BY_DEFAULT
-
-      cattr_accessor :time_zone_aware_attributes, :instance_writer => false
-      self.time_zone_aware_attributes = false
-
-      class_inheritable_accessor :skip_time_zone_conversion_for_attributes, :instance_writer => false
-      self.skip_time_zone_conversion_for_attributes = []
     end
 
     # Declare and check for suffixed attribute methods.
@@ -60,42 +51,32 @@ module ActiveRecord
         @@attribute_method_regexp.match(method_name)
       end
 
-
       # Contains the names of the generated attribute methods.
       def generated_methods #:nodoc:
         @generated_methods ||= Set.new
       end
-      
+
       def generated_methods?
         !generated_methods.empty?
       end
-      
+
       # Generates all the attribute related methods for columns in the database
       # accessors, mutators and query methods.
       def define_attribute_methods
         return if generated_methods?
-        columns_hash.each do |name, column|
-          unless instance_method_already_implemented?(name)
-            if self.serialized_attributes[name]
-              define_read_method_for_serialized_attribute(name)
-            elsif create_time_zone_conversion_attribute?(name, column)
-              define_read_method_for_time_zone_conversion(name)
-            else
-              define_read_method(name.to_sym, name, column)
-            end
-          end
-
-          unless instance_method_already_implemented?("#{name}=")
-            if create_time_zone_conversion_attribute?(name, column)
-              define_write_method_for_time_zone_conversion(name)
-            else  
-              define_write_method(name.to_sym)
+        columns_hash.keys.each do |name|
+          # TODO: Generate for all defined suffixes
+          ["", "=", "?"].each do |suffix|
+            method_name = "#{name}#{suffix}"
+            unless instance_method_already_implemented?(method_name)
+              generate_method = "define_attribute_method#{suffix}"
+              if respond_to?(generate_method)
+                send(generate_method, name)
+              else
+                evaluate_attribute_method(name, "def #{method_name}(*args); attribute#{suffix}('#{name}', *args); end", method_name)
+              end
             end
           end
-
-          unless instance_method_already_implemented?("#{name}?")
-            define_question_method(name)
-          end
         end
       end
 
@@ -104,14 +85,12 @@ module ActiveRecord
       # method is defined by Active Record though.
       def instance_method_already_implemented?(method_name)
         method_name = method_name.to_s
-        return true if method_name =~ /^id(=$|\?$|$)/
+        return true if method_name =~ /^id(=$|\?$|$)/ # TODO: Check against all defined suffixes
         @_defined_class_methods         ||= ancestors.first(ancestors.index(ActiveRecord::Base)).sum([]) { |m| m.public_instance_methods(false) | m.private_instance_methods(false) | m.protected_instance_methods(false) }.map {|m| m.to_s }.to_set
         @@_defined_activerecord_methods ||= (ActiveRecord::Base.public_instance_methods(false) | ActiveRecord::Base.private_instance_methods(false) | ActiveRecord::Base.protected_instance_methods(false)).map{|m| m.to_s }.to_set
         raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
         @_defined_class_methods.include?(method_name)
       end
-      
-      alias :define_read_methods :define_attribute_methods
 
       # +cache_attributes+ allows you to declare which converted attribute values should
       # be cached. Usually caching only pays off for attributes with expensive conversion
@@ -133,83 +112,18 @@ module ActiveRecord
       end
 
       private
-
         # Suffixes a, ?, c become regexp /(a|\?|c)$/
         def rebuild_attribute_method_regexp
           suffixes = attribute_method_suffixes.map { |s| Regexp.escape(s) }
           @@attribute_method_regexp = /(#{suffixes.join('|')})$/.freeze
         end
 
-        # Default to =, ?, _before_type_cast
         def attribute_method_suffixes
           @@attribute_method_suffixes ||= []
         end
-        
-        def create_time_zone_conversion_attribute?(name, column)
-          time_zone_aware_attributes && !skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
-        end
-        
-        # Define an attribute reader method.  Cope with nil column.
-        def define_read_method(symbol, attr_name, column)
-          cast_code = column.type_cast_code('v') if column
-          access_code = cast_code ? "(v=@attributes['#{attr_name}']) && #{cast_code}" : "@attributes['#{attr_name}']"
-
-          unless attr_name.to_s == self.primary_key.to_s
-            access_code = access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless @attributes.has_key?('#{attr_name}'); ")
-          end
-          
-          if cache_attribute?(attr_name)
-            access_code = "@attributes_cache['#{attr_name}'] ||= (#{access_code})"
-          end
-          evaluate_attribute_method attr_name, "def #{symbol}; #{access_code}; end"
-        end
-
-        # Define read method for serialized attribute.
-        def define_read_method_for_serialized_attribute(attr_name)
-          evaluate_attribute_method attr_name, "def #{attr_name}; unserialize_attribute('#{attr_name}'); end"
-        end
-        
-        # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
-        # This enhanced read method automatically converts the UTC time stored in the database to the time zone stored in Time.zone.
-        def define_read_method_for_time_zone_conversion(attr_name)
-          method_body = <<-EOV
-            def #{attr_name}(reload = false)
-              cached = @attributes_cache['#{attr_name}']
-              return cached if cached && !reload
-              time = read_attribute('#{attr_name}')
-              @attributes_cache['#{attr_name}'] = time.acts_like?(:time) ? time.in_time_zone : time
-            end
-          EOV
-          evaluate_attribute_method attr_name, method_body
-        end
-
-        # Defines a predicate method <tt>attr_name?</tt>.
-        def define_question_method(attr_name)
-          evaluate_attribute_method attr_name, "def #{attr_name}?; query_attribute('#{attr_name}'); end", "#{attr_name}?"
-        end
-
-        def define_write_method(attr_name)
-          evaluate_attribute_method attr_name, "def #{attr_name}=(new_value);write_attribute('#{attr_name}', new_value);end", "#{attr_name}="
-        end
-        
-        # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
-        # This enhanced write method will automatically convert the time passed to it to the zone stored in Time.zone.
-        def define_write_method_for_time_zone_conversion(attr_name)
-          method_body = <<-EOV
-            def #{attr_name}=(time)
-              unless time.acts_like?(:time)
-                time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue time
-              end
-              time = time.in_time_zone rescue nil if time
-              write_attribute(:#{attr_name}, time)
-            end
-          EOV
-          evaluate_attribute_method attr_name, method_body, "#{attr_name}="
-        end
 
         # Evaluate the definition for an attribute related method
-        def evaluate_attribute_method(attr_name, method_definition, method_name=attr_name)
-
+        def evaluate_attribute_method(attr_name, method_definition, method_name)
           unless method_name.to_s == primary_key.to_s
             generated_methods << method_name
           end
@@ -225,8 +139,7 @@ module ActiveRecord
             end
           end
         end
-    end #  ClassMethods
-
+    end
 
     # Allows access to the object attributes, which are held in the <tt>@attributes</tt> hash, as though they
     # were first-class methods. So a Person class with a name attribute can use Person#name and
@@ -248,7 +161,7 @@ module ActiveRecord
           return self.send(method_id, *args, &block)
         end
       end
-      
+
       guard_private_attribute_method!(method_name, args)
       if self.class.primary_key.to_s == method_name
         id
@@ -266,80 +179,6 @@ module ActiveRecord
       end
     end
 
-    # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
-    # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
-    def read_attribute(attr_name)
-      attr_name = attr_name.to_s
-      if !(value = @attributes[attr_name]).nil?
-        if column = column_for_attribute(attr_name)
-          if unserializable_attribute?(attr_name, column)
-            unserialize_attribute(attr_name)
-          else
-            column.type_cast(value)
-          end
-        else
-          value
-        end
-      else
-        nil
-      end
-    end
-
-    def read_attribute_before_type_cast(attr_name)
-      @attributes[attr_name]
-    end
-
-    # Returns true if the attribute is of a text column and marked for serialization.
-    def unserializable_attribute?(attr_name, column)
-      column.text? && self.class.serialized_attributes[attr_name]
-    end
-
-    # Returns the unserialized object of the attribute.
-    def unserialize_attribute(attr_name)
-      unserialized_object = object_from_yaml(@attributes[attr_name])
-
-      if unserialized_object.is_a?(self.class.serialized_attributes[attr_name]) || unserialized_object.nil?
-        @attributes.frozen? ? unserialized_object : @attributes[attr_name] = unserialized_object
-      else
-        raise SerializationTypeMismatch,
-          "#{attr_name} was supposed to be a #{self.class.serialized_attributes[attr_name]}, but was a #{unserialized_object.class.to_s}"
-      end
-    end
-  
-
-    # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+. Empty strings for fixnum and float
-    # columns are turned into +nil+.
-    def write_attribute(attr_name, value)
-      attr_name = attr_name.to_s
-      @attributes_cache.delete(attr_name)
-      if (column = column_for_attribute(attr_name)) && column.number?
-        @attributes[attr_name] = convert_number_column_value(value)
-      else
-        @attributes[attr_name] = value
-      end
-    end
-
-
-    def query_attribute(attr_name)
-      unless value = read_attribute(attr_name)
-        false
-      else
-        column = self.class.columns_hash[attr_name]
-        if column.nil?
-          if Numeric === value || value !~ /[^0-9]/
-            !value.to_i.zero?
-          else
-            return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
-            !value.blank?
-          end
-        elsif column.number?
-          !value.zero?
-        else
-          !value.blank?
-        end
-      end
-    end
-    
     # A Person object with a name attribute can ask <tt>person.respond_to?(:name)</tt>,
     # <tt>person.respond_to?(:name=)</tt>, and <tt>person.respond_to?(:name?)</tt>
     # which will all return +true+.
@@ -358,7 +197,7 @@ module ActiveRecord
           return true
         end
       end
-        
+
       if @attributes.nil?
         return super
       elsif @attributes.include?(method_name)
@@ -376,24 +215,9 @@ module ActiveRecord
           raise NoMethodError.new("Attempt to call private method", method_name, args)
         end
       end
-    
+
       def missing_attribute(attr_name, stack)
         raise ActiveRecord::MissingAttributeError, "missing attribute: #{attr_name}", stack
       end
-      
-      # Handle *? for method_missing.
-      def attribute?(attribute_name)
-        query_attribute(attribute_name)
-      end
-
-      # Handle *= for method_missing.
-      def attribute=(attribute_name, value)
-        write_attribute(attribute_name, value)
-      end
-
-      # Handle *_before_type_cast for method_missing.
-      def attribute_before_type_cast(attribute_name)
-        read_attribute_before_type_cast(attribute_name)
-      end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
new file mode 100644
index 0000000000..65845c4d9a
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
@@ -0,0 +1,21 @@
+module ActiveRecord
+  module AttributeMethods
+    module BeforeTypeCast
+      extend ActiveSupport::Concern
+
+      included do
+        attribute_method_suffix "_before_type_cast"
+      end
+
+      def read_attribute_before_type_cast(attr_name)
+        @attributes[attr_name]
+      end
+
+      private
+        # Handle *_before_type_cast for method_missing.
+        def attribute_before_type_cast(attribute_name)
+          read_attribute_before_type_cast(attribute_name)
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
new file mode 100644
index 0000000000..b88c84938d
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -0,0 +1,187 @@
+module ActiveRecord
+  module AttributeMethods
+    # Track unsaved attribute changes.
+    #
+    # A newly instantiated object is unchanged:
+    #   person = Person.find_by_name('uncle bob')
+    #   person.changed?       # => false
+    #
+    # Change the name:
+    #   person.name = 'Bob'
+    #   person.changed?       # => true
+    #   person.name_changed?  # => true
+    #   person.name_was       # => 'uncle bob'
+    #   person.name_change    # => ['uncle bob', 'Bob']
+    #   person.name = 'Bill'
+    #   person.name_change    # => ['uncle bob', 'Bill']
+    #
+    # Save the changes:
+    #   person.save
+    #   person.changed?       # => false
+    #   person.name_changed?  # => false
+    #
+    # Assigning the same value leaves the attribute unchanged:
+    #   person.name = 'Bill'
+    #   person.name_changed?  # => false
+    #   person.name_change    # => nil
+    #
+    # Which attributes have changed?
+    #   person.name = 'bob'
+    #   person.changed        # => ['name']
+    #   person.changes        # => { 'name' => ['Bill', 'bob'] }
+    #
+    # Before modifying an attribute in-place:
+    #   person.name_will_change!
+    #   person.name << 'by'
+    #   person.name_change    # => ['uncle bob', 'uncle bobby']
+    module Dirty
+      extend ActiveSupport::Concern
+
+      DIRTY_SUFFIXES = ['_changed?', '_change', '_will_change!', '_was']
+
+      included do
+        attribute_method_suffix *DIRTY_SUFFIXES
+
+        alias_method_chain :save,            :dirty
+        alias_method_chain :save!,           :dirty
+        alias_method_chain :update,          :dirty
+        alias_method_chain :reload,          :dirty
+
+        superclass_delegating_accessor :partial_updates
+        self.partial_updates = true
+      end
+
+      # Do any attributes have unsaved changes?
+      #   person.changed? # => false
+      #   person.name = 'bob'
+      #   person.changed? # => true
+      def changed?
+        !changed_attributes.empty?
+      end
+
+      # List of attributes with unsaved changes.
+      #   person.changed # => []
+      #   person.name = 'bob'
+      #   person.changed # => ['name']
+      def changed
+        changed_attributes.keys
+      end
+
+      # Map of changed attrs => [original value, new value].
+      #   person.changes # => {}
+      #   person.name = 'bob'
+      #   person.changes # => { 'name' => ['bill', 'bob'] }
+      def changes
+        changed.inject({}) { |h, attr| h[attr] = attribute_change(attr); h }
+      end
+
+      # Attempts to +save+ the record and clears changed attributes if successful.
+      def save_with_dirty(*args) #:nodoc:
+        if status = save_without_dirty(*args)
+          changed_attributes.clear
+        end
+        status
+      end
+
+      # Attempts to <tt>save!</tt> the record and clears changed attributes if successful.
+      def save_with_dirty!(*args) #:nodoc:
+        status = save_without_dirty!(*args)
+        changed_attributes.clear
+        status
+      end
+
+      # <tt>reload</tt> the record and clears changed attributes.
+      def reload_with_dirty(*args) #:nodoc:
+        record = reload_without_dirty(*args)
+        changed_attributes.clear
+        record
+      end
+
+      private
+        # Map of change <tt>attr => original value</tt>.
+        def changed_attributes
+          @changed_attributes ||= {}
+        end
+
+        # Handle <tt>*_changed?</tt> for +method_missing+.
+        def attribute_changed?(attr)
+          changed_attributes.include?(attr)
+        end
+
+        # Handle <tt>*_change</tt> for +method_missing+.
+        def attribute_change(attr)
+          [changed_attributes[attr], __send__(attr)] if attribute_changed?(attr)
+        end
+
+        # Handle <tt>*_was</tt> for +method_missing+.
+        def attribute_was(attr)
+          attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
+        end
+
+        # Handle <tt>*_will_change!</tt> for +method_missing+.
+        def attribute_will_change!(attr)
+          changed_attributes[attr] = clone_attribute_value(:read_attribute, attr)
+        end
+
+        # Wrap write_attribute to remember original attribute value.
+        def write_attribute(attr, value)
+          attr = attr.to_s
+
+          # The attribute already has an unsaved change.
+          if changed_attributes.include?(attr)
+            old = changed_attributes[attr]
+            changed_attributes.delete(attr) unless field_changed?(attr, old, value)
+          else
+            old = clone_attribute_value(:read_attribute, attr)
+            changed_attributes[attr] = old if field_changed?(attr, old, value)
+          end
+
+          # Carry on.
+          super(attr, value)
+        end
+
+        def update_with_dirty
+          if partial_updates?
+            # Serialized attributes should always be written in case they've been
+            # changed in place.
+            update_without_dirty(changed | self.class.serialized_attributes.keys)
+          else
+            update_without_dirty
+          end
+        end
+
+        def field_changed?(attr, old, value)
+          if column = column_for_attribute(attr)
+            if column.number? && column.null && (old.nil? || old == 0) && value.blank?
+              # For nullable numeric columns, NULL gets stored in database for blank (i.e. '') values.
+              # Hence we don't record it as a change if the value changes from nil to ''.
+              # If an old value of 0 is set to '' we want this to get changed to nil as otherwise it'll
+              # be typecast back to 0 (''.to_i => 0)
+              value = nil
+            else
+              value = column.type_cast(value)
+            end
+          end
+
+          old != value
+        end
+
+      module ClassMethods
+        def self.extended(base)
+          class << base
+            alias_method_chain :alias_attribute, :dirty
+          end
+        end
+
+        def alias_attribute_with_dirty(new_name, old_name)
+          alias_attribute_without_dirty(new_name, old_name)
+          DIRTY_SUFFIXES.each do |suffix|
+            module_eval <<-STR, __FILE__, __LINE__+1
+              def #{new_name}#{suffix}; self.#{old_name}#{suffix}; end  # def subject_changed?; self.title_changed?; end
+            STR
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attribute_methods/query.rb b/activerecord/lib/active_record/attribute_methods/query.rb
new file mode 100644
index 0000000000..a949d80120
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/query.rb
@@ -0,0 +1,37 @@
+module ActiveRecord
+  module AttributeMethods
+    module Query
+      extend ActiveSupport::Concern
+
+      included do
+        attribute_method_suffix "?"
+      end
+
+      def query_attribute(attr_name)
+        unless value = read_attribute(attr_name)
+          false
+        else
+          column = self.class.columns_hash[attr_name]
+          if column.nil?
+            if Numeric === value || value !~ /[^0-9]/
+              !value.to_i.zero?
+            else
+              return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
+              !value.blank?
+            end
+          elsif column.number?
+            !value.zero?
+          else
+            !value.blank?
+          end
+        end
+      end
+
+      private
+        # Handle *? for method_missing.
+        def attribute?(attribute_name)
+          query_attribute(attribute_name)
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
new file mode 100644
index 0000000000..9f948536fc
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -0,0 +1,79 @@
+module ActiveRecord
+  module AttributeMethods
+    module Read
+      extend ActiveSupport::Concern
+
+      # included do
+      #   attribute_method_suffix ""
+      # end
+
+      module ClassMethods
+        protected
+          def define_attribute_method(attr_name)
+            if self.serialized_attributes[attr_name]
+              define_read_method_for_serialized_attribute(attr_name)
+            else
+              define_read_method(attr_name.to_sym, attr_name, columns_hash[attr_name])
+            end
+          end
+
+        private
+          # Define read method for serialized attribute.
+          def define_read_method_for_serialized_attribute(attr_name)
+            evaluate_attribute_method attr_name, "def #{attr_name}; unserialize_attribute('#{attr_name}'); end", attr_name
+          end
+
+          # Define an attribute reader method.  Cope with nil column.
+          def define_read_method(symbol, attr_name, column)
+            cast_code = column.type_cast_code('v') if column
+            access_code = cast_code ? "(v=@attributes['#{attr_name}']) && #{cast_code}" : "@attributes['#{attr_name}']"
+
+            unless attr_name.to_s == self.primary_key.to_s
+              access_code = access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless @attributes.has_key?('#{attr_name}'); ")
+            end
+
+            if cache_attribute?(attr_name)
+              access_code = "@attributes_cache['#{attr_name}'] ||= (#{access_code})"
+            end
+            evaluate_attribute_method attr_name, "def #{symbol}; #{access_code}; end", attr_name
+          end
+      end
+
+      # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
+      # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
+      def read_attribute(attr_name)
+        attr_name = attr_name.to_s
+        if !(value = @attributes[attr_name]).nil?
+          if column = column_for_attribute(attr_name)
+            if unserializable_attribute?(attr_name, column)
+              unserialize_attribute(attr_name)
+            else
+              column.type_cast(value)
+            end
+          else
+            value
+          end
+        else
+          nil
+        end
+      end
+
+      # Returns true if the attribute is of a text column and marked for serialization.
+      def unserializable_attribute?(attr_name, column)
+        column.text? && self.class.serialized_attributes[attr_name]
+      end
+
+      # Returns the unserialized object of the attribute.
+      def unserialize_attribute(attr_name)
+        unserialized_object = object_from_yaml(@attributes[attr_name])
+
+        if unserialized_object.is_a?(self.class.serialized_attributes[attr_name]) || unserialized_object.nil?
+          @attributes.frozen? ? unserialized_object : @attributes[attr_name] = unserialized_object
+        else
+          raise SerializationTypeMismatch,
+            "#{attr_name} was supposed to be a #{self.class.serialized_attributes[attr_name]}, but was a #{unserialized_object.class.to_s}"
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
new file mode 100644
index 0000000000..f379b4c0f8
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -0,0 +1,60 @@
+module ActiveRecord
+  module AttributeMethods
+    module TimeZoneConversion
+      extend ActiveSupport::Concern
+
+      included do
+        cattr_accessor :time_zone_aware_attributes, :instance_writer => false
+        self.time_zone_aware_attributes = false
+
+        class_inheritable_accessor :skip_time_zone_conversion_for_attributes, :instance_writer => false
+        self.skip_time_zone_conversion_for_attributes = []
+      end
+
+      module ClassMethods
+        protected
+          # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
+          # This enhanced read method automatically converts the UTC time stored in the database to the time zone stored in Time.zone.
+          def define_attribute_method(attr_name)
+            if create_time_zone_conversion_attribute?(attr_name, columns_hash[attr_name])
+              method_body = <<-EOV
+                def #{attr_name}(reload = false)
+                  cached = @attributes_cache['#{attr_name}']
+                  return cached if cached && !reload
+                  time = read_attribute('#{attr_name}')
+                  @attributes_cache['#{attr_name}'] = time.acts_like?(:time) ? time.in_time_zone : time
+                end
+              EOV
+              evaluate_attribute_method attr_name, method_body, attr_name
+            else
+              super
+            end
+          end
+
+          # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
+          # This enhanced write method will automatically convert the time passed to it to the zone stored in Time.zone.
+          def define_attribute_method=(attr_name)
+            if create_time_zone_conversion_attribute?(attr_name, columns_hash[attr_name])
+              method_body = <<-EOV
+                def #{attr_name}=(time)
+                  unless time.acts_like?(:time)
+                    time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue time
+                  end
+                  time = time.in_time_zone rescue nil if time
+                  write_attribute(:#{attr_name}, time)
+                end
+              EOV
+              evaluate_attribute_method attr_name, method_body, "#{attr_name}="
+            else
+              super
+            end
+          end
+
+        private
+          def create_time_zone_conversion_attribute?(name, column)
+            time_zone_aware_attributes && !skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
new file mode 100644
index 0000000000..aab816899c
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -0,0 +1,36 @@
+module ActiveRecord
+  module AttributeMethods
+    module Write
+      extend ActiveSupport::Concern
+
+      included do
+        attribute_method_suffix "="
+      end
+
+      module ClassMethods
+        protected
+          def define_attribute_method=(attr_name)
+            evaluate_attribute_method attr_name, "def #{attr_name}=(new_value); write_attribute('#{attr_name}', new_value); end", "#{attr_name}="
+          end
+      end
+
+      # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+. Empty strings for fixnum and float
+      # columns are turned into +nil+.
+      def write_attribute(attr_name, value)
+        attr_name = attr_name.to_s
+        @attributes_cache.delete(attr_name)
+        if (column = column_for_attribute(attr_name)) && column.number?
+          @attributes[attr_name] = convert_number_column_value(value)
+        else
+          @attributes[attr_name] = value
+        end
+      end
+
+      private
+        # Handle *= for method_missing.
+        def attribute=(attribute_name, value)
+          write_attribute(attribute_name, value)
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 5a36ff5ba2..f3cb905754 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3212,7 +3212,9 @@ module ActiveRecord #:nodoc:
     include Validations
     include Locking::Optimistic, Locking::Pessimistic
     include AttributeMethods
-    include Dirty
+    include AttributeMethods::Read, AttributeMethods::Write, AttributeMethods::BeforeTypeCast, AttributeMethods::Query
+    include AttributeMethods::TimeZoneConversion
+    include AttributeMethods::Dirty
     include Callbacks, ActiveModel::Observing, Timestamp
     include Associations, AssociationPreload, NamedScope
     include ActiveModel::Conversion
diff --git a/activerecord/lib/active_record/dirty.rb b/activerecord/lib/active_record/dirty.rb
deleted file mode 100644
index 178767e0c3..0000000000
--- a/activerecord/lib/active_record/dirty.rb
+++ /dev/null
@@ -1,186 +0,0 @@
-module ActiveRecord
-  # Track unsaved attribute changes.
-  #
-  # A newly instantiated object is unchanged:
-  #   person = Person.find_by_name('uncle bob')
-  #   person.changed?       # => false
-  #
-  # Change the name:
-  #   person.name = 'Bob'
-  #   person.changed?       # => true
-  #   person.name_changed?  # => true
-  #   person.name_was       # => 'uncle bob'
-  #   person.name_change    # => ['uncle bob', 'Bob']
-  #   person.name = 'Bill'
-  #   person.name_change    # => ['uncle bob', 'Bill']
-  #
-  # Save the changes:
-  #   person.save
-  #   person.changed?       # => false
-  #   person.name_changed?  # => false
-  #
-  # Assigning the same value leaves the attribute unchanged:
-  #   person.name = 'Bill'
-  #   person.name_changed?  # => false
-  #   person.name_change    # => nil
-  #
-  # Which attributes have changed?
-  #   person.name = 'bob'
-  #   person.changed        # => ['name']
-  #   person.changes        # => { 'name' => ['Bill', 'bob'] }
-  #
-  # Before modifying an attribute in-place:
-  #   person.name_will_change!
-  #   person.name << 'by'
-  #   person.name_change    # => ['uncle bob', 'uncle bobby']
-  module Dirty
-    extend ActiveSupport::Concern
-
-    DIRTY_SUFFIXES = ['_changed?', '_change', '_will_change!', '_was']
-
-    included do
-      attribute_method_suffix *DIRTY_SUFFIXES
-
-      alias_method_chain :write_attribute, :dirty
-      alias_method_chain :save,            :dirty
-      alias_method_chain :save!,           :dirty
-      alias_method_chain :update,          :dirty
-      alias_method_chain :reload,          :dirty
-
-      superclass_delegating_accessor :partial_updates
-      self.partial_updates = true
-    end
-
-    # Do any attributes have unsaved changes?
-    #   person.changed? # => false
-    #   person.name = 'bob'
-    #   person.changed? # => true
-    def changed?
-      !changed_attributes.empty?
-    end
-
-    # List of attributes with unsaved changes.
-    #   person.changed # => []
-    #   person.name = 'bob'
-    #   person.changed # => ['name']
-    def changed
-      changed_attributes.keys
-    end
-
-    # Map of changed attrs => [original value, new value].
-    #   person.changes # => {}
-    #   person.name = 'bob'
-    #   person.changes # => { 'name' => ['bill', 'bob'] }
-    def changes
-      changed.inject({}) { |h, attr| h[attr] = attribute_change(attr); h }
-    end
-
-    # Attempts to +save+ the record and clears changed attributes if successful.
-    def save_with_dirty(*args) #:nodoc:
-      if status = save_without_dirty(*args)
-        changed_attributes.clear
-      end
-      status
-    end
-
-    # Attempts to <tt>save!</tt> the record and clears changed attributes if successful.
-    def save_with_dirty!(*args) #:nodoc:
-      status = save_without_dirty!(*args)
-      changed_attributes.clear
-      status
-    end
-
-    # <tt>reload</tt> the record and clears changed attributes.
-    def reload_with_dirty(*args) #:nodoc:
-      record = reload_without_dirty(*args)
-      changed_attributes.clear
-      record
-    end
-
-    private
-      # Map of change <tt>attr => original value</tt>.
-      def changed_attributes
-        @changed_attributes ||= {}
-      end
-
-      # Handle <tt>*_changed?</tt> for +method_missing+.
-      def attribute_changed?(attr)
-        changed_attributes.include?(attr)
-      end
-
-      # Handle <tt>*_change</tt> for +method_missing+.
-      def attribute_change(attr)
-        [changed_attributes[attr], __send__(attr)] if attribute_changed?(attr)
-      end
-
-      # Handle <tt>*_was</tt> for +method_missing+.
-      def attribute_was(attr)
-        attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
-      end
-
-      # Handle <tt>*_will_change!</tt> for +method_missing+.
-      def attribute_will_change!(attr)
-        changed_attributes[attr] = clone_attribute_value(:read_attribute, attr)
-      end
-
-      # Wrap write_attribute to remember original attribute value.
-      def write_attribute_with_dirty(attr, value)
-        attr = attr.to_s
-
-        # The attribute already has an unsaved change.
-        if changed_attributes.include?(attr)
-          old = changed_attributes[attr]
-          changed_attributes.delete(attr) unless field_changed?(attr, old, value)
-        else
-          old = clone_attribute_value(:read_attribute, attr)
-          changed_attributes[attr] = old if field_changed?(attr, old, value)
-        end
-
-        # Carry on.
-        write_attribute_without_dirty(attr, value)
-      end
-
-      def update_with_dirty
-        if partial_updates?
-          # Serialized attributes should always be written in case they've been
-          # changed in place.
-          update_without_dirty(changed | self.class.serialized_attributes.keys)
-        else
-          update_without_dirty
-        end
-      end
-
-      def field_changed?(attr, old, value)
-        if column = column_for_attribute(attr)
-          if column.number? && column.null && (old.nil? || old == 0) && value.blank?
-            # For nullable numeric columns, NULL gets stored in database for blank (i.e. '') values.
-            # Hence we don't record it as a change if the value changes from nil to ''.
-            # If an old value of 0 is set to '' we want this to get changed to nil as otherwise it'll
-            # be typecast back to 0 (''.to_i => 0)
-            value = nil
-          else
-            value = column.type_cast(value)
-          end
-        end
-
-        old != value
-      end
-
-    module ClassMethods
-      def self.extended(base)
-        class << base
-          alias_method_chain :alias_attribute, :dirty
-        end
-      end
-
-      def alias_attribute_with_dirty(new_name, old_name)
-        alias_attribute_without_dirty(new_name, old_name)
-        DIRTY_SUFFIXES.each do |suffix|
-          module_eval <<-STR, __FILE__, __LINE__+1
-            def #{new_name}#{suffix}; self.#{old_name}#{suffix}; end  # def subject_changed?; self.title_changed?; end
-          STR
-        end
-      end
-    end
-  end
-end