1 files changed, 18 insertions, 10 deletions

diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index cf17b1d8a4..936a18d99a 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -1,4 +1,3 @@
-
 module ActiveRecord
   # = Active Record Timestamp
   #
@@ -10,9 +9,9 @@ module ActiveRecord
   #
   #   config.active_record.record_timestamps = false
   #
-  # Timestamps are in the local timezone by default but you can use UTC by setting:
+  # Timestamps are in UTC by default but you can use the local timezone by setting:
   #
-  #   config.active_record.default_timezone = :utc
+  #   config.active_record.default_timezone = :local
   #
   # == Time Zone aware attributes
   #
@@ -37,19 +36,20 @@ module ActiveRecord
     end
 
     def initialize_dup(other) # :nodoc:
-      clear_timestamp_attributes
       super
+      clear_timestamp_attributes
     end
 
   private
 
-    def create
+    def _create_record
       if self.record_timestamps
         current_time = current_time_from_proper_timezone
 
         all_timestamp_attributes.each do |column|
-          if respond_to?(column) && respond_to?("#{column}=") && self.send(column).nil?
-            write_attribute(column.to_s, current_time)
+          column = column.to_s
+          if has_attribute?(column) && !attribute_present?(column)
+            write_attribute(column, current_time)
           end
         end
       end
@@ -57,7 +57,7 @@ module ActiveRecord
       super
     end
 
-    def update(*args)
+    def _update_record(*args)
       if should_record_timestamps?
         current_time = current_time_from_proper_timezone
 
@@ -71,7 +71,7 @@ module ActiveRecord
     end
 
     def should_record_timestamps?
-      self.record_timestamps && (!partial_writes? || changed? || (attributes.keys & self.class.serialized_attributes.keys).present?)
+      self.record_timestamps && (!partial_writes? || changed?)
     end
 
     def timestamp_attributes_for_create_in_model
@@ -98,6 +98,14 @@ module ActiveRecord
       timestamp_attributes_for_create + timestamp_attributes_for_update
     end
 
+    def max_updated_column_timestamp(timestamp_names = timestamp_attributes_for_update)
+      timestamp_names
+        .map { |attr| self[attr] }
+        .compact
+        .map(&:to_time)
+        .max
+    end
+
     def current_time_from_proper_timezone
       self.class.default_timezone == :utc ? Time.now.utc : Time.now
     end
@@ -106,7 +114,7 @@ module ActiveRecord
     def clear_timestamp_attributes
       all_timestamp_attributes_in_model.each do |attribute_name|
         self[attribute_name] = nil
-        changed_attributes.delete(attribute_name)
+        clear_attribute_changes([attribute_name])
       end
     end
   end