AI: address issue #242

Co-authored-by: Codex Night Worker <codex-night@localhost>
Reviewed-on: #480
Co-authored-by: miteruzo <miteruzo@naver.com>

backend/db/migrate/20261116000000_add_index_to_tags_post_count.rb

@@ -0,0 +1,5 @@
+class AddIndexToTagsPostCount < ActiveRecord::Migration[8.0]
+  def change
+    add_index :tags, :post_count
+  end
+end

backend/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: 2026_11_08_020000) do
+ActiveRecord::Schema[8.0].define(version: 2026_11_16_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -629,6 +629,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_11_08_020000) do
     t.integer "post_count", default: 0, null: false
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
+    t.index ["post_count"], name: "index_tags_on_post_count"
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
   end

backend/spec/models/tag_spec.rb

@@ -2,6 +2,17 @@ require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
   include WikiRecords
+
+  describe 'database indexes' do
+    it 'has a non-unique index on post_count' do
+      indexes = described_class.connection.indexes(described_class.table_name)
+      index = indexes.find { |entry| entry.columns == ['post_count'] }
+
+      expect(index).to be_present
+      expect(index.unique).to be(false)
+    end
+  end
+
   describe '#has_description?' do
     let(:tag) { create(:tag) }