Add index to created_at on attachment and pictures tables

We have the recent scope on the attachment and pictures models.
Also the picture archive now defaults to sorting by recent images.

On large projects it should be a good idea to have an index on these
columns.

It will add the index concurrently on Postgres.

Author: tvdeyen

db/migrate/20250905140323_add_created_at_index_to_pictures_and_attachments.rb

@@ -0,0 +1,14 @@
+class AddCreatedAtIndexToPicturesAndAttachments < ActiveRecord::Migration[7.1]
+  disable_ddl_transaction! if connection.adapter_name.match?(/postgres/i)
+
+  def change
+    add_index :alchemy_pictures, :created_at, if_not_exists: true, algorithm: algorithm
+    add_index :alchemy_attachments, :created_at, if_not_exists: true, algorithm: algorithm
+  end
+
+  private
+
+  def algorithm
+    connection.adapter_name.match?(/postgres/i) ? :concurrently : nil
+  end
+end

spec/dummy/db/migrate/20250905140502_add_created_at_index_to_pictures_and_attachments.alchemy.rb

@@ -0,0 +1,15 @@
+# This migration comes from alchemy (originally 20250905140323)
+class AddCreatedAtIndexToPicturesAndAttachments < ActiveRecord::Migration[7.1]
+  disable_ddl_transaction! if connection.adapter_name.match?(/postgres/i)
+
+  def change
+    add_index :alchemy_pictures, :created_at, if_not_exists: true, algorithm: algorithm
+    add_index :alchemy_attachments, :created_at, if_not_exists: true, algorithm: algorithm
+  end
+
+  private
+
+  def algorithm
+    connection.adapter_name.match?(/postgres/i) ? :concurrently : nil
+  end
+end

spec/dummy/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_06_26_160417) do
+ActiveRecord::Schema[8.0].define(version: 2025_09_05_140502) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -49,6 +49,7 @@
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "file_uid"
+    t.index ["created_at"], name: "index_alchemy_attachments_on_created_at"
     t.index ["creator_id"], name: "index_alchemy_attachments_on_creator_id"
     t.index ["file_uid"], name: "index_alchemy_attachments_on_file_uid"
     t.index ["updater_id"], name: "index_alchemy_attachments_on_updater_id"
@@ -246,6 +247,7 @@
     t.string "image_file_uid"
     t.integer "image_file_size"
     t.string "image_file_format"
+    t.index ["created_at"], name: "index_alchemy_pictures_on_created_at"
     t.index ["creator_id"], name: "index_alchemy_pictures_on_creator_id"
     t.index ["image_file_name"], name: "index_alchemy_pictures_on_image_file_name"
     t.index ["name"], name: "index_alchemy_pictures_on_name"