touch now always inserts null in object_changes

[Fixes #1121]

CHANGELOG.md

@@ -18,6 +18,8 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
   - This change fixes a long-standing issue with reification of STI subclasses,
     [#594](https://github.com/paper-trail-gem/paper_trail/issues/594)
 - Removed `touch_with_version`, was deprecated in 9.0.0
+- [#1121](https://github.com/paper-trail-gem/paper_trail/issues/1121) -
+  `touch` now always inserts `null` in `object_changes`.
 
 ### Added
 

lib/paper_trail/events/update.rb

@@ -11,7 +11,7 @@ module PaperTrail
       # - is_touch - [boolean] - Used in the two situations that are touch-like:
       #   - `after_touch` we call `RecordTrail#record_update`
       # - force_changes - [Hash] - Only used by `RecordTrail#update_columns`,
-      #   because there dirty tracking is off, so it has to track its own changes.
+      #   because there dirty-tracking is off, so it has to track its own changes.
       #
       # @api private
       def initialize(record, in_after_callback, is_touch, force_changes)
@@ -37,6 +37,19 @@ module PaperTrail
         end
         merge_metadata_into(data)
       end
+
+      private
+
+      # `touch` cannot record `object_changes` because rails' `touch` does not
+      # perform dirty-tracking. Specifically, methods from `Dirty`, like
+      # `saved_changes`, return the same values before and after `touch`.
+      #
+      # See https://github.com/rails/rails/issues/33429
+      #
+      # @api private
+      def record_object_changes?
+        !@is_touch && super
+      end
     end
   end
 end

lib/paper_trail/record_trail.rb

@@ -268,9 +268,10 @@ module PaperTrail
     # creates a version to record those changes.
     # @api public
     def update_columns(attributes)
-      # `@record.update_columns` skips dirty tracking, so we can't just use `@record.changes` or
-      # @record.saved_changes` from `ActiveModel::Dirty`. We need to build our own hash with the
-      # changes that will be made directly to the database.
+      # `@record.update_columns` skips dirty-tracking, so we can't just use
+      # `@record.changes` or @record.saved_changes` from `ActiveModel::Dirty`.
+      # We need to build our own hash with the changes that will be made
+      # directly to the database.
       changes = {}
       attributes.each do |k, v|
         changes[k] = [@record[k], v]

spec/paper_trail/events/update_spec.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+module PaperTrail
+  module Events
+    ::RSpec.describe Update do
+      describe "#data", versioning: true do
+        context "is_touch false" do
+          it "object_changes is present" do
+            carter = Family::CelebrityFamily.create(
+              name: "Carter",
+              path_to_stardom: "Mexican radio"
+            )
+            carter.path_to_stardom = "Johnny"
+            data = PaperTrail::Events::Update.new(carter, false, false, nil).data
+            expect(data[:object_changes]).to eq(
+              <<~YAML
+                ---
+                path_to_stardom:
+                - Mexican radio
+                - Johnny
+              YAML
+            )
+          end
+        end
+
+        context "is_touch true" do
+          it "object_changes is nil" do
+            carter = Family::CelebrityFamily.create(
+              name: "Carter",
+              path_to_stardom: "Mexican radio"
+            )
+            carter.path_to_stardom = "Johnny"
+            data = PaperTrail::Events::Update.new(carter, false, true, nil).data
+            expect(data[:object_changes]).to be_nil
+          end
+        end
+      end
+    end
+  end
+end