Google\Cloud\Datastore\Operation::rollback PHP Method

    public function rollback($transactionId)
    {
        $this->connection->rollback(['projectId' => $this->projectId, 'transaction' => $transactionId]);
    }

 /**
  * Roll back a Transaction
  *
  * Example:
  * ```
  * $transaction->rollback();
  * ```
  *
  * @return void
  */
 public function rollback()
 {
     return $this->operation->rollback($this->transactionId);
 }