Don't allow access if user has already taken part

Signed-off-by: Marcel Klehr <mklehr@gmx.net>

lib/Migration/Version0010Date20190000000007.php

@@ -0,0 +1,77 @@
+<?php
+/**
+ * @copyright Copyright (c) 2017 René Gieling <github@dartcafe.de>
+ *
+ * @author Marcel Klehr <mklehr@gmx.net>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as
+ *  published by the Free Software Foundation, either version 3 of the
+ *  License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Forms\Migration;
+
+use Doctrine\DBAL\Exception\TableNotFoundException;
+use Doctrine\DBAL\Platforms\PostgreSqlPlatform;
+use Doctrine\DBAL\Types\Type;
+use OCP\DB\ISchemaWrapper;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IConfig;
+use OCP\IDBConnection;
+use OCP\Migration\SimpleMigrationStep;
+use OCP\Migration\IOutput;
+
+/**
+ * Installation class for the forms app.
+ * Initial db creation
+ */
+class Version0010Date20190000000007 extends SimpleMigrationStep {
+
+	/** @var IDBConnection */
+	protected $connection;
+
+	/** @var IConfig */
+	protected $config;
+
+	/**
+	 * @param IDBConnection $connection
+	 * @param IConfig $config
+	 */
+	public function __construct(IDBConnection $connection, IConfig $config) {
+		$this->connection = $connection;
+		$this->config = $config;
+	}
+
+	/**
+	 * @param IOutput $output
+	 * @param \Closure $schemaClosure The `\Closure` returns a `ISchemaWrapper`
+	 * @param array $options
+	 * @return null|ISchemaWrapper
+	 * @since 13.0.0
+	 */
+	public function changeSchema(IOutput $output, \Closure $schemaClosure, array $options) {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+
+		if ($schema->hasTable('forms_events')) {
+			$schema->getTable('forms_events')->addColumn('unique', Type::INTEGER, [
+				'notnull' => false,
+				'default' => 0,
+			]);
+		} else {
+		}
+		return $schema;
+	}
+}