MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 3: Commands

Command Object Example

The code in this example shows how to create and execute a command object.

/////////////////////////////////////////////////////////////////
// myCreateCommand
//
// This function takes an IUnknown pointer on a session object
// and attempts to create a command object using the session's
// IDBCreateCommand interface. Since this interface is optional,
// this may fail.
//
/////////////////////////////////////////////////////////////////
HRESULT   myCreateCommand
   (
   IUnknown *           pUnkSession,
   IUnknown **          ppUnkCommand
   )
{
   HRESULT              hr;
   IDBCreateCommand *   pIDBCreateCommand = NULL;
   
   // Attempt to create a command object from the session object.
   XCHECK_HR(hr = pUnkSession->QueryInterface(
             IID_IDBCreateCommand, (void**)&pIDBCreateCommand));
   XCHECK_HR(hr = pIDBCreateCommand->CreateCommand(
             NULL,             // pUnkOuter
             IID_ICommand,     // riid
             ppUnkCommand));   // ppCommand

CLEANUP:
   if( pIDBCreateCommand )
      pIDBCreateCommand->Release();
   return hr;
}




/////////////////////////////////////////////////////////////////
// myExecuteCommand
//
// This function takes an IUnknown pointer on a command 
// object and performs the following steps to create a new 
// rowset object:
//  - Sets the given properties on the command object; these
//     properties will be applied by the provider to any rowset
//     created by this command.
//  - Sets the given command text for the command.
//  - Executes the command to create a new rowset object.
//
/////////////////////////////////////////////////////////////////
HRESULT   myExecuteCommand
   (
   IUnknown *             pUnkCommand,
   WCHAR *                pwszCommandText,
   ULONG                  cPropSets,
   DBPROPSET*             rgPropSets,
   IUnknown **            ppUnkRowset
   )
{
   HRESULT                hr;
   ICommandText *         pICommandText          = NULL;
   ICommandProperties *   vpICommandProperties   = NULL;

   // Set the properties on the command object.
   XCHECK_HR(hr = pUnkCommand->QueryInterface(
             IID_ICommandProperties, (void**)&pICommandProperties));
   XCHECK_HR(hr = pICommandProperties->SetProperties(cPropSets, 
             rgPropSets));

   // Set the text for this command, using the default command text
   // dialect. All providers that support commands must support this
   // dialect, and providers that support SQL must be able to recognize
   // an SQL command as SQL when this dialect is specified.
   XCHECK_HR(hr = pUnkCommand->QueryInterface(
             IID_ICommandText, (void**)&pICommandText));
   XCHECK_HR(hr = pICommandText->SetCommandText(
             DBGUID_DEFAULT,      // guidDialect
             pwszCommandText));   // pwszCommandText

   // And execute the command. Note that the user could have
   // entered a non-row returning command, so we will check for
   // that and return failure to prevent the display of the
   // nonexistent rowset by the caller.
   XCHECK_HR(hr = pICommandText->Execute(   
             NULL,            // pUnkOuter
             IID_IRowset,     // riid
             NULL,            // pParams
             NULL,            // pcRowsAffected
             ppUnkRowset));   // ppRowset

   if( !*ppUnkRowset )
   {
      printf("\nThe command executed successfully, but did not " \
             "return a rowset.\nNo rowset will be displayed.\n");
      hr = E_FAIL;
   }


CLEANUP:
   if( pICommandText )
      pICommandText->Release();
   if( pICommandProperties )
      pICommandProperties->Release();
   return hr;
}