perf: Add index for group_folders table

appinfo/info.xml

@@ -13,7 +13,7 @@ Folders can be configured from *Group folders* in the admin settings.
 
 After a folder is created, the admin can give access to the folder to one or more groups, control their write/sharing permissions and assign a quota for the folder.
 ]]></description>
-	<version>19.0.0-dev.3</version>
+	<version>19.0.0-dev.4</version>
 	<licence>agpl</licence>
 	<author>Robin Appelman</author>
 	<namespace>GroupFolders</namespace>

lib/Migration/Version19000Date20241029123147.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\GroupFolders\Migration;
+
+use Closure;
+use OCP\DB\ISchemaWrapper;
+use OCP\Migration\IOutput;
+use OCP\Migration\SimpleMigrationStep;
+
+class Version19000Date20241029123147 extends SimpleMigrationStep {
+	/**
+	 * @param Closure(): ISchemaWrapper $schemaClosure
+	 */
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options): ?ISchemaWrapper {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+
+		if ($schema->hasTable('group_folders')) {
+			$table = $schema->getTable('group_folders');
+			if (!$table->hasIndex('gf_folders_folder_id')) {
+				$table->addUniqueIndex(['folder_id'], 'gf_folders_folder_id');
+				return $schema;
+			}
+		}
+
+		return null;
+	}
+}