14.1.61. tablet_qt/db/dbtransaction.h

/*
    Copyright (C) 2012-2019 Rudolf Cardinal (rudolf@pobox.com).

    This file is part of CamCOPS.

    CamCOPS is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    CamCOPS 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with CamCOPS. If not, see <http://www.gnu.org/licenses/>.
*/

#pragma once
class DatabaseManager;


// Represents an SQL transaction.
//
// In general, consider AVOIDING this and using DbNestableTransaction
// instead. DbTransaction uses BEGIN TRANSACTION/COMMIT/ROLLBACK, and so
// if you accidentally nest it, things go wrong.
// DbNestableTransaction uses SAVEPOINT x/RELEASE x/ROLLBACK TO SAVEPOINT x
// instead, which is safely nestable as long as x is transaction-specific,
// and RELEASE behaves like COMMIT when it reaches the top level.

class DbTransaction
{
public:
    // Create the transaction. It starts in a "successful" state.
    DbTransaction(DatabaseManager& db);

    // When the transaction is destroyed, it commits or rolls back depending
    // on whether it's been told of failure or not.
    ~DbTransaction();

    // Mark the transaction as a failure.
    void fail();

    // Mark the transaction as successful.
    void succeed();
protected:

    // Our database manager.
    DatabaseManager& m_db;

    // Have we failed?
    bool m_fail;
};