Transactions

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Transactions ensure that a group of changes is applied "all or nothing".

Methods

DB::startTransaction();   // начать
DB::commit();             // подтвердить
DB::rollback();           // откатить

Nested transactions are supported (via nested_transactions - internal levels are emulated by the savepoint logic of the transaction manager).

Action after commit

External HTTP, sending emails, posting to social networks and other irreversible actions do not run until the database is confirmed. Register the callback:

DB::startTransaction();
try {
    DB::Insert($orders, $order);
    DB::afterCommit(function () use ($order) {
        OrderNotifications::created($order);
    });
    DB::commit();
} catch (\Throwable $e) {
    DB::rollback();
    throw $e;
}

Inside the transaction, the callback is executed after the successful external commit(). When rollback() it is being deleted. If there is no active transaction, DB::afterCommit() executes the callback immediately. The callback exception is logged and cannot be canceled already confirmed transaction, so the integration must be idempotent.

Basic pattern

Always wrap the body in try/catch and rollback on the error:

DB::startTransaction();
try {
    DB::Insert($orders, $order);
    $orderId = (int) DB::insertId();

    foreach ($items as $item) {
        $item['order_id'] = $orderId;
        DB::Insert($orderItems, $item);
    }

    DB::Update($stock, array('qty' => DB::sqlEval('qty - 1')), 'id = %i', $productId);

    DB::commit();
} catch (\Throwable $e) {
    DB::rollback();
    throw $e;   // или обработать/залогировать
}

When needed

Several related entries must be applied together (order + items + balances).
Batch operations where partial results are not allowed.
Transfer/recalculation of data.

When not needed

Single INSERT/UPDATE/DELETE - it is already atomic.
Read only (SELECT).

Pitfalls

Don't forget commit() - without it, changes will be rolled back upon completion of the request.
Do not mix with DDL (ALTER, CREATE) - in MySQL they cause an implicit commit.
Keep the transaction short: do not make external HTTP calls inside it and long operations - this keeps the blocking.

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