Denormalise change notes

app/models/change_note.rb

@@ -1,9 +1,24 @@
 class ChangeNote < ApplicationRecord
-  belongs_to :edition, optional: true
+  belongs_to :edition
+  belongs_to :document
+
+  before_validation :set_columns_from_edition
 
   def self.create_from_edition(payload, edition)
     ChangeNoteFactory.new(payload, edition).build
   end
+
+private
+
+  def set_columns_from_edition
+    if edition.nil?
+      errors.add(:edition, "must exist")
+      raise_validation_error
+    end
+
+    self.document_id = edition.document_id
+    self.user_facing_version = edition.user_facing_version
+  end
 end
 
 class ChangeNoteFactory

app/presenters/queries/change_history.rb

@@ -30,8 +30,7 @@ def notes_for_edition_and_linked_content_blocks
 
       def change_notes_for_edition
         ChangeNote
-          .joins(:edition)
-          .where(editions: { document: edition.document })
+          .where(document_id: edition.document_id)
           .where("user_facing_version <= ?", edition.user_facing_version)
           .where.not(public_timestamp: nil)
       end

db/migrate/20251128170548_add_document_id_to_change_notes.rb

@@ -0,0 +1,5 @@
+class AddDocumentIdToChangeNotes < ActiveRecord::Migration[8.0]
+  def change
+    add_column :change_notes, :document_id, :integer
+  end
+end

db/migrate/20251128171122_add_user_facing_version_to_change_notes.rb

@@ -0,0 +1,5 @@
+class AddUserFacingVersionToChangeNotes < ActiveRecord::Migration[8.0]
+  def change
+    add_column :change_notes, :user_facing_version, :integer
+  end
+end

db/migrate/20251128172013_add_index_on_change_notes_document_id.rb

@@ -0,0 +1,11 @@
+class AddIndexOnChangeNotesDocumentId < ActiveRecord::Migration[8.0]
+  disable_ddl_transaction!
+
+  def change
+    add_index :change_notes,
+              :document_id,
+              where: "public_timestamp IS NOT NULL",
+              algorithm: :concurrently,
+              name: "idx_change_notes_document_id_partial"
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_11_21_132638) do
+ActiveRecord::Schema[8.0].define(version: 2025_11_28_172013) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -41,6 +41,9 @@
     t.integer "edition_id", null: false
     t.datetime "created_at", precision: nil
     t.datetime "updated_at", precision: nil
+    t.integer "document_id"
+    t.integer "user_facing_version"
+    t.index ["document_id"], name: "idx_change_notes_document_id_partial", where: "(public_timestamp IS NOT NULL)"
     t.index ["edition_id"], name: "index_change_notes_on_edition_id"
   end
 

spec/models/change_note_spec.rb

@@ -13,6 +13,22 @@
     )
   end
 
+  describe "#save!" do
+    it "won't save without an edition" do
+      change_note = described_class.new
+      expect { change_note.save! }.to raise_error(ActiveRecord::RecordInvalid, /Edition must exist/)
+    end
+
+    it "sets document_id and user_facing_version from edition" do
+      change_note = described_class.new
+      change_note.edition = edition
+      change_note.save!
+      change_note.reload
+      expect(change_note.document_id).to eq(edition.document_id)
+      expect(change_note.user_facing_version).to eq(edition.user_facing_version)
+    end
+  end
+
   describe ".create_from_edition" do
     subject { described_class.create_from_edition(payload, edition) }