Condividi tramite

Ottenere un cursore FAST_FORWARD

  • Articolo

Per ottenere un cursore forward-only di sola lettura, impostare le proprietà del set di righe DBPROP_SERVERCURSOR, DBPROP_OTHERINSERT, DBPROP_OTHERUPDATEDELETE, DBPROP_OWNINSERT e DBPROP_OWNUPDATEDELETE su VARIANT_TRUE.

In un esempio completo viene illustrato come impostare le proprietà del set di righe per ottenere un cursore FAST_FORWARD. Dopo che le proprietà sono state impostate, viene eseguita un'istruzione SELECT per recuperare e visualizzare la colonna Name della tabella Purchasing.Vendor del database AdventureWorks.

Importante

Se possibile, usare l'autenticazione di Windows. Se non è disponibile, agli utenti verrà richiesto di immettere le credenziali in fase di esecuzione. Evitare di archiviare le credenziali in un file. Se è necessario rendere persistenti le credenziali, è consigliabile crittografarle usando l'API di crittografia Win32.

Per ottenere un cursore FAST_FORWARD

  1. Stabilire una connessione all'origine dati.

  2. Impostare le proprietà del set di righe DBPROP_SERVERCURSOR, DBPROP_OTHERINSERT, DBPROP_OTHERUPDATEDELETE, DBPROP_OWNINSERT e DBPROP_OWNUPDATEDELETE su VARIANT_TRUE.

  3. Eseguire il comando.

Esempio

Nell'esempio seguente viene illustrato come impostare le proprietà di un set di righe in modo da ottenere un cursore FAST_FORWARD. Una volta impostate le proprietà, viene eseguita un'istruzione SELECT per recuperare e visualizzare la colonna Name della tabella Purchasing.Vendor del database AdventureWorks. Questo esempio non è supportato in IA64.

Per l'esempio è necessario il database di esempio AdventureWorks, che è possibile scaricare dalla home page del sito relativo a progetti della community ed esempi per Microsoft SQL Server.

Compilare il listato di codice C++ seguente con ole32.lib oleaut32.lib ed eseguirlo. In questa applicazione viene eseguita la connessione all'istanza predefinita di SQL Server nel computer in uso. In alcuni sistemi operativi Windows sarà necessario modificare (local) o (localhost) impostando il valore sul nome dell'istanza di SQL Server. Per connettersi a un'istanza denominata, modificare la stringa di connessione da L"(local)" in L"(local)\\nome", dove nome rappresenta l'istanza denominata. Per impostazione predefinita, SQL Server Express viene installato in un'istanza denominata. Verificare che nella variabile di ambiente INCLUDE sia presente la directory che contiene sqlncli.h.

// compile with: ole32.lib oleaut32.lib  
#define INITGUID  
#define DBINITCONSTANTS  
#define OLEDBVER 0x0250   // to include correct interfaces  
  
#include <windows.h>  
#include <stdio.h>  
#include <oledb.h>  
#include <sqlncli.h>  
#include <oledberr.h>  
  
IDBInitialize* pIDBInitialize = NULL;  
ICommandText* pICommandText = NULL;  
  
// Connect to the server and create a command object.  
int InitializeAndConnect();  
  
// Set the properties to get a FAST_FORWARD cursor.  
int SetRowsetProperties();  
  
// This function executes a command and displays the results.  
int ExecuteAndDisplay();  
  
// Release memory.  
void Cleanup();  
  
int main() {  
   if (InitializeAndConnect() == -1) {  
      // Handle error.  
      printf("Failed to initialize and connect to the server.\n");  
      return -1;  
   }  
  
   // Set the row properties to FAST_FORWARD cursor.  
   if (SetRowsetProperties() == -1) {  
      // Handle error.  
      printf("Failed to set the rowset properties.\n");  
      return -1;  
   }  
  
   // Execute a command and display the results.  
   if (ExecuteAndDisplay() == -1) {  
      // Handle error.  
      printf("Failed to execute a command and display the results.\n");  
      return -1;  
   }  
  
   Cleanup();  
}  
  
int InitializeAndConnect() {  
   HRESULT hr = S_OK;  
  
   IDBProperties* pIDBProperties = NULL;  
   IDBCreateSession* pIDBCreateSession = NULL;  
   IDBCreateCommand* pIDBCreateCommand = NULL;  
  
   DBPROPSET dbPropSet;  
   DBPROP dbProp[4];  
   int iRetVal = 0;  
  
   // Initialize OLE  
   if ( FAILED( hr = OleInitialize( NULL ) ) ) {  
      // Handle errors here.  
      return -1;  
   }  
  
   // Create an instance of Microsoft SQL Server Native Client OLE DB Provider.  
   if ( FAILED( hr =   
      CoCreateInstance(CLSID_SQLNCLI11, NULL, CLSCTX_INPROC_SERVER, IID_IDBProperties, (void **) &pIDBProperties ))) {  
      // Handle errors here.  
      return -1;  
   }  
  
   // Set up the connection properties.  
   dbProp[0].dwPropertyID = DBPROP_INIT_DATASOURCE;  
   dbProp[0].dwOptions = DBPROPOPTIONS_REQUIRED;  
   dbProp[0].colid = DB_NULLID;  
   V_VT(&(dbProp[0].vValue)) = VT_BSTR;  
  
   V_BSTR(&(dbProp[0].vValue)) = SysAllocString( L"(local)" );  
  
   dbProp[1].dwPropertyID = DBPROP_AUTH_INTEGRATED;  
   dbProp[1].dwOptions = DBPROPOPTIONS_REQUIRED;  
   dbProp[1].colid = DB_NULLID;  
   V_VT(&(dbProp[1].vValue)) = VT_BSTR;  
   V_BSTR(&(dbProp[1].vValue)) = SysAllocString( L"SSPI" );  
  
   dbProp[2].dwPropertyID = DBPROP_NULLCOLLATION;  
   dbProp[2].dwOptions = DBPROPOPTIONS_REQUIRED;  
   dbProp[2].colid = DB_NULLID;  
   V_VT(&(dbProp[2].vValue)) = VT_BSTR;  
   V_BSTR(&(dbProp[2].vValue)) = SysAllocString( L"" );  
  
   dbProp[3].dwPropertyID = DBPROP_INIT_CATALOG;  
   dbProp[3].dwOptions = DBPROPOPTIONS_REQUIRED;  
   dbProp[3].colid = DB_NULLID;  
   V_VT(&(dbProp[3].vValue)) = VT_BSTR;  
   V_BSTR(&(dbProp[3].vValue)) = SysAllocString( L"AdventureWorks" );  
  
   dbPropSet.rgProperties = dbProp;  
   dbPropSet.cProperties = 4;  
   dbPropSet.guidPropertySet = DBPROPSET_DBINIT;  
  
   if ( FAILED( hr = pIDBProperties->SetProperties( 1, &dbPropSet ))) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   SysFreeString( V_BSTR(&(dbProp[0].vValue)) );  
   SysFreeString( V_BSTR(&(dbProp[1].vValue)) );  
   SysFreeString( V_BSTR(&(dbProp[2].vValue)) );  
   SysFreeString( V_BSTR(&(dbProp[3].vValue)) );  
  
   // Get an IDBInitialize interface.  
   if ( FAILED( hr =   
      pIDBProperties->QueryInterface( IID_IDBInitialize, (void **) &pIDBInitialize ))) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Call Initialize.  
   if ( FAILED( hr = pIDBInitialize->Initialize())) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Get a IDBCreateSession interface.  
   if ( FAILED( hr =   
      pIDBInitialize->QueryInterface( IID_IDBCreateSession, (void **) &pIDBCreateSession ))) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Create a session  
   if ( FAILED( hr =   
      pIDBCreateSession->CreateSession( NULL, IID_IDBCreateCommand, (IUnknown **) &pIDBCreateCommand))) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Create a command.  
   if ( FAILED( hr =   
      pIDBCreateCommand->CreateCommand( NULL, IID_ICommandText, (IUnknown **) &pICommandText))) {  
      // Handle errors here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
CLEANUP:  
   // Release all the objects not needed anymore.  
   pIDBProperties->Release();  
   if ( pIDBCreateSession )  
      pIDBCreateSession->Release();  
   if ( pIDBCreateCommand )  
      pIDBCreateCommand->Release();  
  
   return iRetVal;  
}  
  
int SetRowsetProperties() {  
   HRESULT hr = S_OK;  
   ICommandProperties* pICommandProperties = NULL;  
   DBPROPSET dbPropSet;  
   DBPROP dbProp[5];  
   int iRetVal = 0;  
  
   // Get an ICommandProperties object.  
   if ( FAILED( hr =   
      pICommandText->QueryInterface( IID_ICommandProperties, (void **) &pICommandProperties ))) {  
      // Handle errors here.  
      return -1;  
   }  
  
   // Set up the properties to get a FAST_FORWARD cursor.  
   dbProp[0].dwPropertyID       = DBPROP_SERVERCURSOR;  
   dbProp[0].dwOptions          = DBPROPOPTIONS_REQUIRED;  
   dbProp[0].colid              = DB_NULLID;  
   V_VT(&(dbProp[0].vValue))    = VT_BOOL;  
   V_BOOL(&(dbProp[0].vValue))  = VARIANT_TRUE;  
  
   dbProp[1].dwPropertyID       = DBPROP_OTHERINSERT;  
   dbProp[1].dwOptions          = DBPROPOPTIONS_REQUIRED;  
   dbProp[1].colid              = DB_NULLID;  
   V_VT(&(dbProp[1].vValue))    = VT_BOOL;  
   V_BOOL(&(dbProp[1].vValue))  = VARIANT_TRUE;  
  
   dbProp[2].dwPropertyID       = DBPROP_OTHERUPDATEDELETE;  
   dbProp[2].dwOptions          = DBPROPOPTIONS_REQUIRED;  
   dbProp[2].colid              = DB_NULLID;  
   V_VT(&(dbProp[2].vValue))    = VT_BOOL;  
   V_BOOL(&(dbProp[2].vValue))  = VARIANT_TRUE;  
  
   dbProp[3].dwPropertyID       = DBPROP_OWNINSERT;  
   dbProp[3].dwOptions          = DBPROPOPTIONS_REQUIRED;  
   dbProp[3].colid              = DB_NULLID;  
   V_VT(&(dbProp[3].vValue))    = VT_BOOL;  
   V_BOOL(&(dbProp[3].vValue))  = VARIANT_TRUE;  
  
   dbProp[4].dwPropertyID       = DBPROP_OWNUPDATEDELETE;  
   dbProp[4].dwOptions          = DBPROPOPTIONS_REQUIRED;  
   dbProp[4].colid              = DB_NULLID;  
   V_VT(&(dbProp[4].vValue))    = VT_BOOL;  
   V_BOOL(&(dbProp[4].vValue))  = VARIANT_TRUE;  
  
   dbPropSet.rgProperties       = dbProp;  
   dbPropSet.cProperties        = 5;  
   dbPropSet.guidPropertySet    = DBPROPSET_ROWSET;  
  
   if ( FAILED( hr = pICommandProperties->SetProperties( 1, &dbPropSet))) {  
      // Handle errors here.  
      iRetVal = -1;  
   }  
  
   // Release the ICommandProperties object.  
   pICommandProperties->Release();  
  
   return iRetVal;  
}  
  
int ExecuteAndDisplay() {  
   HRESULT hr = S_OK;  
   IRowset* pIRowset = NULL;  
   IAccessor* pIAccessor = NULL;  
  
   BYTE* pData = NULL;  
   DBCOUNTITEM cRowsObtained = 0;  
   ULONG cCount = 0;  
  
   HROW* pRows = new HROW[10];  
   HACCESSOR hAccessor = 0;  
   DBBINDING Bind[1];  
   int iRetVal = 0;  
  
   if (!pRows)  
      return -1;  
  
   // Set the command text.  
   if ( FAILED( hr = pICommandText->SetCommandText( DBGUID_SQL, L"select Name from Purchasing.Vendor")))  
      // Handle errors and free the memory here.  
      return -1;  
  
   // Execute the command.  
   if ( FAILED( hr = pICommandText->Execute( NULL, IID_IRowset, NULL, NULL, (IUnknown **) &pIRowset )))  
      // Handle errors and free the memory here.  
      return -1;  
  
    // Set up the binding structure for Name (nvarchar(50)).  
    Bind[0].dwPart      = DBPART_VALUE;  
    Bind[0].eParamIO    = DBPARAMIO_NOTPARAM;  
    Bind[0].iOrdinal    = 1;  
    Bind[0].pTypeInfo   = NULL;  
    Bind[0].pObject     = NULL;  
    Bind[0].pBindExt    = NULL;  
    Bind[0].dwFlags     = 0;  
    Bind[0].dwMemOwner  = DBMEMOWNER_CLIENTOWNED;  
    Bind[0].obLength    = 0;  
    Bind[0].obStatus    = 0;  
    Bind[0].obValue     = 0;  
    Bind[0].cbMaxLen    = 102;  
    Bind[0].wType       = DBTYPE_WSTR;  
    Bind[0].bPrecision  = 0;  
    Bind[0].bScale      = 0;  
  
   // Get an IAccessor interface.  
   if ( FAILED( hr = pIRowset->QueryInterface( IID_IAccessor, (void **) &pIAccessor))) {  
      // Handle errors and free the memory here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Create an accessor.  
   if ( FAILED( hr =   
      pIAccessor->CreateAccessor(  DBACCESSOR_ROWDATA, 1, Bind, 0, &hAccessor, NULL))) {  
      // Handle errors and free the memory here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Allocate memory for the data.  
   pData = new BYTE[102];  
   if (!(pData /* = new BYTE[102] */ )) {  
      // Handle errors and free the memory here.  
      iRetVal = -1;  
      goto CLEANUP;  
   }  
  
   // Loop through all of the rows.  
   for ( ; ; ) {  
      if (FAILED( hr = pIRowset->GetNextRows( NULL, 0, 10, &cRowsObtained, &pRows))) {  
         // Handle errors and free the memory here.  
         iRetVal = -1;  
         goto CLEANUP;  
      }  
  
      // Make sure some rows were obtained.  
      if (cRowsObtained == 0)  
         break;  
  
      // Get the data for the each of the rows.  
      for ( cCount = 0 ; cCount < cRowsObtained ; cCount++ ) {  
         // Get the row data needed.  
         if ( FAILED( hr = pIRowset->GetData( pRows[cCount], hAccessor, pData ))) {  
            // Handle errors and free the memory here.  
            iRetVal = -1;  
            goto CLEANUP;  
         }  
  
         // Display row data.  
         printf( "%S\n", pData);  
      }  
  
      // Release the rows.  
      if ( FAILED( hr = pIRowset->ReleaseRows(cRowsObtained, pRows, NULL, NULL, NULL ))) {  
         // Handle errors and free the memory here.  
         iRetVal = -1;  
         goto CLEANUP;  
      }  
   }  
  
CLEANUP:  
   // Release memory allocated for the data.  
   delete [] pRows;  
   delete [] pData;  
  
   // Release the HACCESSOR.  
   if (pIAccessor) {  
      pIAccessor->ReleaseAccessor( hAccessor, NULL );  
  
      // Release the IAccessor object.  
      pIAccessor->Release();  
   }  
  
   // Release the rowset.  
   pIRowset->Release();  
  
   return iRetVal;  
}  
  
void Cleanup() {  
   HRESULT hr = S_OK;  
  
   // Release the ICommandText object.  
   pICommandText->Release();  
  
   // Uninitialize the IDBInitialize object.  
   if ( FAILED( hr = pIDBInitialize->Uninitialize())) {  
      // Handle errors here.  
   }  
  
   // Release the IDBInitialize object.  
   pIDBInitialize->Release();  
  
   // Uninitialize OLE.  
   OleUninitialize();  
}