Dando suporte a transações distribuídas

Os consumidores do provedor OLE DB do SQL Server Native Client podem usar o método ITransactionJoin::JoinTransaction para participar de uma transação distribuída coordenada pelo MS DTC (Microsoft Distributed Transaction Coordinator).

O MS DTC expõe objetos COM que permitem que os clientes iniciem e participem de transações coordenadas através de várias conexões com vários repositórios de dados. Para iniciar uma transação, o consumidor do provedor OLE DB do SQL Server Native Client usa a interface ITransactionDispenser do MS DTC. O membro BeginTransaction de ITransactionDispenser retorna uma referência a um objeto de transação distribuída. Essa referência é passada ao provedor OLE DB do SQL Server Native Client usando JoinTransaction.

O MS DTC dá suporte à confirmação e à anulação assíncronas de transações distribuídas. Para notificação do status da transação assíncrona, o consumidor implementa a interface ITransactionOutcomeEvents e a conecta a um objeto de transação do MS DTC.

Para transações distribuídas, o provedor OLE DB do SQL Server Native Client implementa os parâmetros de ITransactionJoin::JoinTransaction conforme indicado a seguir.

Este exemplo coordena a transação usando o MS DTC.

// Interfaces used in the example.
IDBCreateSession*       pIDBCreateSession   = NULL;
ITransactionJoin*       pITransactionJoin   = NULL;
IDBCreateCommand*       pIDBCreateCommand   = NULL;
IRowset*                pIRowset            = NULL;

// Transaction dispenser and transaction from MS DTC.
ITransactionDispenser*  pITransactionDispenser = NULL;
ITransaction*           pITransaction       = NULL;

    HRESULT             hr;

// Get the command creation interface for the session.
if (FAILED(hr = pIDBCreateSession->CreateSession(NULL,
     IID_IDBCreateCommand, (IUnknown**) &pIDBCreateCommand)))
    {
    // Process error from session creation. Release any references and
    // return.
    }

// Get a transaction dispenser object from MS DTC and
// start a transaction.
if (FAILED(hr = DtcGetTransactionManager(NULL, NULL,
    IID_ITransactionDispenser, 0, 0, NULL,
    (void**) &pITransactionDispenser)))
    {
    // Process error message from MS DTC, release any references,
    // and then return.
    }
if (FAILED(hr = pITransactionDispenser->BeginTransaction(
    NULL, ISOLATIONLEVEL_READCOMMITTED, ISOFLAG_RETAIN_DONTCARE,
    NULL, &pITransaction)))
    {
    // Process error message from MS DTC, release any references,
    // and then return.
    }

// Join the transaction.
if (FAILED(pIDBCreateCommand->QueryInterface(IID_ITransactionJoin,
    (void**) &pITransactionJoin)))
    {
    // Process failure to get an interface, release any references, and
    // then return.
    }
if (FAILED(pITransactionJoin->JoinTransaction(
    (IUnknown*) pITransaction, 0, 0, NULL)))
    {
    // Process join failure, release any references, and then return.
    }

// Get data into a rowset, then update the data. Functions are not
// illustrated in this example.
if (FAILED(hr = ExecuteCommand(pIDBCreateCommand, &pIRowset)))
    {
    // Release any references and return.
    }

// If rowset data update fails, then terminate the transaction, else
// commit. The example doesn't retain the rowset.
if (FAILED(hr = UpdateDataInRowset(pIRowset, bDelayedUpdate)))
    {
    // Get error from update, then abort.
    pITransaction->Abort(NULL, FALSE, FALSE);
    }
else
    {
    if (FAILED(hr = pITransaction->Commit(FALSE, 0, 0)))
        {
        // Get error from failed commit.
        //
        // If a distributed commit fails, application logic could
        // analyze failure and retry. In this example, terminate. The 
        // consumer must resolve this somehow.
        pITransaction->Abort(NULL, FALSE, FALSE);
        }
    }

if (FAILED(hr))
    {
    // Update of data or commit failed. Release any references and
    // return.
    }

// Un-enlist from the distributed transaction by setting 
// the transaction object pointer to NULL.
if (FAILED(pITransactionJoin->JoinTransaction(
    (IUnknown*) NULL, 0, 0, NULL)))
    {
    // Process failure, and then return.
    }

// Release any references and continue.