add the ability to track changes on destroy

this involved refactoring the internal serialization code so it'd be possible to run it on non-Rails-provided changes

CHANGELOG.md

@@ -26,6 +26,7 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
 - [#1099](/~https://github.com/paper-trail-gem/paper_trail/issues/1099) -
   Ability to save ~50% storage space by making the `object` column optional.
   Note that this disables `reify` and `where_object`.
+- Ability to track `object_changes` on destroy, to complement ⬆️.
 
 ### Fixed
 

README.md

@@ -1291,6 +1291,14 @@ The `object` column ends up storing a lot of duplicate data if you have models t
 and that are updated many times. You can save ~50% of storage space by removing the column from the
 versions table. It's important to note that this will disable `reify` and `where_object`.
 
+Removing the `object` column also makes it so that destroy events don't store any attributes, since
+the default behavior on destroy is only to populate the `object` column.
+That can be fixed with this setting:
+
+```ruby
+PaperTrail.config.record_changes_on_destroy = true
+```
+
 ## 7. Testing
 
 You may want to turn PaperTrail off to speed up your tests.  See [Turning

lib/paper_trail/config.rb

@@ -13,6 +13,7 @@ class Config
       :classes_warned_about_sti_item_types,
       :i_have_updated_my_existing_item_types,
       :object_changes_adapter,
+      :record_changes_on_destroy,
       :serializer,
       :version_limit
     )

lib/paper_trail/events/base.rb

@@ -119,14 +119,18 @@ def changed_in_latest_version
       end
 
       # @api private
-      def changes
-        notable_changes = changes_in_latest_version.delete_if { |k, _v|
-          !notably_changed.include?(k)
-        }
+      def serialize_changes(changes)
         AttributeSerializers::ObjectChangesAttribute.
           new(@record.class).
-          serialize(notable_changes)
-        notable_changes.to_hash
+          serialize(changes)
+        changes.to_hash
+      end
+
+      # @api private
+      def notable_changes
+        changes_in_latest_version.delete_if { |k, _v|
+          !notably_changed.include?(k)
+        }
       end
 
       # Rails 5.1 changed the API of `ActiveRecord::Dirty`. See

lib/paper_trail/events/create.rb

@@ -20,7 +20,9 @@ def data
           data[:created_at] = @record.updated_at
         end
         if record_object_changes? && changed_notably?
-          data[:object_changes] = recordable_object_changes(changes)
+          changes = serialize_changes(notable_changes)
+          changes = recordable_object_changes(changes)
+          data[:object_changes] = changes
         end
         merge_metadata_into(data)
       end

lib/paper_trail/events/destroy.rb

@@ -21,6 +21,13 @@ def data
         if record_object?
           data[:object] = recordable_object(false)
         end
+        if record_object_changes? && PaperTrail.config.record_changes_on_destroy
+          # Rails' implementation returns nothing on destroy :/
+          changes = @record.attributes.map { |attr, value| [attr, [value, nil]] }.to_h
+          changes = serialize_changes(changes)
+          changes = recordable_object_changes(changes)
+          data[:object_changes] = changes
+        end
         merge_metadata_into(data)
       end
     end

lib/paper_trail/events/update.rb

@@ -17,7 +17,7 @@ class Update < Base
       def initialize(record, in_after_callback, is_touch, force_changes)
         super(record, in_after_callback)
         @is_touch = is_touch
-        @changes = force_changes.nil? ? changes : force_changes
+        @force_changes = force_changes
       end
 
       # Return attributes of nascent `Version` record.
@@ -35,7 +35,10 @@ def data
           data[:object] = recordable_object(@is_touch)
         end
         if record_object_changes?
-          data[:object_changes] = recordable_object_changes(@changes)
+          changes = @force_changes.nil? ? notable_changes : @force_changes
+          changes = serialize_changes(changes)
+          changes = recordable_object_changes(changes)
+          data[:object_changes] = changes
         end
         merge_metadata_into(data)
       end

spec/paper_trail/model_spec.rb

@@ -928,4 +928,19 @@
       end.to raise_error "where_object can't be called without an object column"
     end
   end
+
+  context "record_changes_on_destroy" do
+    before { PaperTrail.config.record_changes_on_destroy = true }
+    after  { PaperTrail.config.record_changes_on_destroy = nil  }
+
+    it "works" do
+      song = Song.create(length: 4)
+      changes = YAML.load song.versions.last.attributes["object_changes"]
+      expect(changes).to eq "id" => [nil, song.id], "length" => [nil, 240]
+
+      song.destroy
+      changes = YAML.load song.versions.last.attributes["object_changes"]
+      expect(changes).to eq "id" => [song.id, nil], "length" => [240, nil], "name" => [nil, nil]
+    end
+  end
 end