server/lib/private/DB/Adapter.php

<?php
/**
 * @copyright Copyright (c) 2016, ownCloud, Inc.
 *
 * @author Bart Visscher <bartv@thisnet.nl>
 * @author Joas Schilling <coding@schilljs.com>
 * @author Jonny007-MKD <1-23-4-5@web.de>
 * @author Morris Jobke <hey@morrisjobke.de>
 * @author Robin Appelman <robin@icewind.nl>
 * @author Thomas Müller <thomas.mueller@tmit.eu>
 *
 * @license AGPL-3.0
 *
 * This code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * 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, version 3,
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */

namespace OC\DB;

use Doctrine\DBAL\Exception\UniqueConstraintViolationException;

/**
 * This handles the way we use to write queries, into something that can be
 * handled by the database abstraction layer.
 */
class Adapter {

	/**
	 * @var \OC\DB\Connection $conn
	 */
	protected $conn;

	public function __construct($conn) {
		$this->conn = $conn;
	}

	/**
	 * @param string $table name
	 * @return int id of last insert statement
	 */
	public function lastInsertId($table) {
		return $this->conn->realLastInsertId($table);
	}

	/**
	 * @param string $statement that needs to be changed so the db can handle it
	 * @return string changed statement
	 */
	public function fixupStatement($statement) {
		return $statement;
	}

	/**
	 * Create an exclusive read+write lock on a table
	 *
	 * @param string $tableName
	 * @since 9.1.0
	 */
	public function lockTable($tableName) {
		$this->conn->beginTransaction();
		$this->conn->executeUpdate('LOCK TABLE `' .$tableName . '` IN EXCLUSIVE MODE');
	}

	/**
	 * Release a previous acquired lock again
	 *
	 * @since 9.1.0
	 */
	public function unlockTable() {
		$this->conn->commit();
	}

	/**
	 * Insert a row if the matching row does not exists. To accomplish proper race condition avoidance
	 * it is needed that there is also a unique constraint on the values. Then this method will
	 * catch the exception and return 0.
	 *
	 * @param string $table The table name (will replace *PREFIX* with the actual prefix)
	 * @param array $input data that should be inserted into the table  (column name => value)
	 * @param array|null $compare List of values that should be checked for "if not exists"
	 *				If this is null or an empty array, all keys of $input will be compared
	 *				Please note: text fields (clob) must not be used in the compare array
	 * @return int number of inserted rows
	 * @throws \Doctrine\DBAL\DBALException
	 * @deprecated 15.0.0 - use unique index and "try { $db->insert() } catch (UniqueConstraintViolationException $e) {}" instead, because it is more reliable and does not have the risk for deadlocks - see https://github.com/nextcloud/server/pull/12371
	 */
	public function insertIfNotExist($table, $input, array $compare = null) {
		if (empty($compare)) {
			$compare = array_keys($input);
		}
		$query = 'INSERT INTO `' .$table . '` (`'
			. implode('`,`', array_keys($input)) . '`) SELECT '
			. str_repeat('?,', count($input)-1).'? ' // Is there a prettier alternative?
			. 'FROM `' . $table . '` WHERE ';

		$inserts = array_values($input);
		foreach($compare as $key) {
			$query .= '`' . $key . '`';
			if (is_null($input[$key])) {
				$query .= ' IS NULL AND ';
			} else {
				$inserts[] = $input[$key];
				$query .= ' = ? AND ';
			}
		}
		$query = substr($query, 0, -5);
		$query .= ' HAVING COUNT(*) = 0';

		try {
			return $this->conn->executeUpdate($query, $inserts);
		} catch (UniqueConstraintViolationException $e) {
			// if this is thrown then a concurrent insert happened between the insert and the sub-select in the insert, that should have avoided it
			// it's fine to ignore this then
			//
			// more discussions about this can be found at https://github.com/nextcloud/server/pull/12315
			return 0;
		}
	}
}