Track changes on destroy (#1123)

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

CHANGELOG.md

@@ -31,6 +31,9 @@ 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`.
+  - `object_changes` is now populated on destroy in order to make
+    `where_object_changes` usable when you've dropped the `object` column.
+    See the issue for a backport migration.
 
 ### Fixed
 

lib/paper_trail/events/base.rb

@@ -119,14 +119,25 @@ module PaperTrail
       end
 
       # @api private
-      def changes
-        notable_changes = changes_in_latest_version.delete_if { |k, _v|
-          !notably_changed.include?(k)
-        }
+      def prepare_object_changes(changes)
+        changes = serialize_object_changes(changes)
+        changes = recordable_object_changes(changes)
+        changes
+      end
+
+      # @api private
+      def serialize_object_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 +20,8 @@ module PaperTrail
           data[:created_at] = @record.updated_at
         end
         if record_object_changes? && changed_notably?
-          data[:object_changes] = recordable_object_changes(changes)
+          changes = notable_changes
+          data[:object_changes] = prepare_object_changes(changes)
         end
         merge_metadata_into(data)
       end

lib/paper_trail/events/destroy.rb

@@ -21,6 +21,11 @@ module PaperTrail
         if record_object?
           data[:object] = recordable_object(false)
         end
+        if record_object_changes?
+          # Rails' implementation returns nothing on destroy :/
+          changes = @record.attributes.map { |attr, value| [attr, [value, nil]] }.to_h
+          data[:object_changes] = prepare_object_changes(changes)
+        end
         merge_metadata_into(data)
       end
     end

lib/paper_trail/events/update.rb

@@ -17,7 +17,7 @@ module PaperTrail
       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 +35,8 @@ module PaperTrail
           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
+          data[:object_changes] = prepare_object_changes(changes)
         end
         merge_metadata_into(data)
       end

spec/models/no_object_spec.rb

@@ -22,8 +22,18 @@ RSpec.describe NoObject, versioning: true do
     a = n.versions.last.attributes
     expect(a).not_to include "object"
     expect(a["event"]).to eq "destroy"
-    expect(a["object_changes"]).to be_nil
+    expect(a["object_changes"]).to start_with("---")
     expect(a["metadatum"]).to eq(42)
+
+    # New feature: destroy populates object_changes
+    # https://github.com/paper-trail-gem/paper_trail/pull/1123
+    h = YAML.safe_load(a["object_changes"], [::Time])
+    expect(h["id"]).to eq([n.id, nil])
+    expect(h["letter"]).to eq([n.letter, nil])
+    expect(h["created_at"][0]).to be_present
+    expect(h["created_at"][1]).to be_nil
+    expect(h["updated_at"][0]).to be_present
+    expect(h["updated_at"][1]).to be_nil
   end
 
   describe "reify" do

spec/paper_trail/model_spec.rb

@@ -264,11 +264,18 @@ RSpec.describe(::PaperTrail, versioning: true) do
           expect(widget.versions.last.item).to be_nil
         end
 
-        it "not have changes" do
-          widget = Widget.create(name: "Henry")
-          widget.update_attributes(name: "Harry")
-          widget.destroy
-          expect(widget.versions.last.changeset).to eq({})
+        it "has changes" do
+          book = Book.create! title: "A"
+          changes = YAML.load book.versions.last.attributes["object_changes"]
+          expect(changes).to eq("id" => [nil, book.id], "title" => [nil, "A"])
+
+          book.update! title: "B"
+          changes = YAML.load book.versions.last.attributes["object_changes"]
+          expect(changes).to eq("title" => %w[A B])
+
+          book.destroy
+          changes = YAML.load book.versions.last.attributes["object_changes"]
+          expect(changes).to eq("id" => [book.id, nil], "title" => ["B", nil])
         end
       end
     end