Transactions

Begin, commit and roll back a unit of work. More...

Classes
class	Transaction
	Unit of work on a database connection. More...
class	AsyncBegin
	Awaitable for asynchronous begin-transaction. More...
class	AsyncCommit
	Awaitable for asynchronous commit. More...
class	AsyncRollback
	Awaitable for asynchronous rollback. More...
class	SqliteTransaction
	SQLite transaction with optional immediate locking. More...

Detailed Description

Transaction is a unit of work on one Connection. The constructor begins a deferred transaction unless the start flag is false. begin() starts one; if a transaction is already active it is rolled back first. commit() ends it and keeps the changes. rollback() ends it and discards them. If the object is destroyed while still active, the destructor rolls back and swallows any error from that rollback.

The object is not copyable. It does not own the connection.

Asynchronous begin, commit and rollback follow the connection model and need setActive() on that connection. beginStart() / endStart() / startFinished() begin the transaction. beginCommit() / endCommit() / commitFinished() commit it. beginRollback() / endRollback() / rollbackFinished() roll it back. endStart() is the call that marks the transaction active on the async path.

C++20 awaitables wrap those pairs: beginAsync(), commitAsync() and rollbackAsync() are used with co_await and complete through the same signals. Only one awaitable may be pending on the connection. Destroying the Transaction while one is in flight detaches it; a later resume throws std::logic_error.

Override onGetBeginSql(), onGetCommitSql() and onGetRollbackSql() to supply backend-specific SQL. A null return lets the backend use its default. SqliteTransaction() uses that hook to run BEGIN IMMEDIATE TRANSACTION when immediate locking is requested.

Pt::Db::Transaction txn(conn);
conn.execute("UPDATE accounts SET balance = balance - 10 WHERE id = 1");
conn.execute("UPDATE accounts SET balance = balance + 10 WHERE id = 2");
txn.commit();