BUG: CDatabase::ExecuteSQL() Function Does Not Throw Exception with Multiple Result Sets

• Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

When the CDatabase::ExecuteSQL function is called on a stored procedure that creates multiple result sets, and an error is encountered, an exception may not be thrown. Note, however, that the exception is thrown only if the error is encountered while processing the first result set. If the error happens after processing the first result set, the exception is not thrown.

The More Information section has an example of a stored procedure that does not cause an exception to be thrown. This stored procedure creates two result sets and calls RAISERROR between them.

CAUSE

The implementation of the ExecuteSQL function of the CDatabase class throws an exception if an error is encountered during the execution of the SQLExecDirect function. The function loops through all the remaining result sets by calling SQLMoreResults, and then exits if it reaches the last result set or if it encounters an error. The function does not, however, throw an exception if an error is encountered in a call to SQLMoreResults.

RESOLUTION

For a workaround, see the "More Information" section.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create the following stored procedure:




CREATE PROCEDURE get_author_titles @au_id id
AS
BEGIN
SELECT * FROM authors where au_id = @au_id
if @@ROWCOUNT = 0
RAISERROR ('No author found',15,10)
else
SELECT title_id FROM titleauthor WHERE au_id = @au_id
END 

2. Create an MFC AppWizard application with database header support. Create a menu handler.



3. Paste the following code into the handler:




	CDatabase db;
	db.OpenEx(_T("DSN=Pubs;UID=sa;PWD=;"));
	try {
		db.ExecuteSQL(_T("EXEC get_author_titles '998-72-3567'"));
		db.ExecuteSQL(_T("EXEC get_author_titles '998-72-3568'"));
	}
	catch (CDBException* pEx)
	{
		TCHAR buff[80];
		pEx->GetErrorMessage(buff,80);
		AfxMessageBox(buff);
		pEx->Delete();
	} 

4. Change the connect string to point to your SQL Server.



5. Compile and run the application. Run the code above.

Workaround

1. Create a CDatabase-derived class called CMyDatabase.



2. Add the following function to the class. This function will override the CDatabase::ExecuteSQL function. The code adds only the two lines indicated to the implementation of the CDatabase::ExecuteSQL function:

   
   void CMyDatabase::ExecuteSQL(LPCTSTR lpszSQL)
   {
   	USES_CONVERSION;
   	RETCODE nRetCode;
   	HSTMT hstmt;
   
   	ASSERT_VALID(this);
   	ASSERT(AfxIsValidString(lpszSQL));
   
   	AFX_SQL_SYNC(::SQLAllocStmt(m_hdbc, &hstmt));
   	if (!CheckHstmt(nRetCode, hstmt))
   		AfxThrowDBException(nRetCode, this, hstmt);
   
   	TRY
   	{
   		OnSetOptions(hstmt);
   
   		// Give derived CDatabase classes option to use parameters.
   		BindParameters(hstmt);
   
   		AFX_ODBC_CALL(::SQLExecDirect(hstmt,
   			(UCHAR*)T2A((LPTSTR)lpszSQL), SQL_NTS));
   
   		if (!CheckHstmt(nRetCode, hstmt))
   			AfxThrowDBException(nRetCode, this, hstmt);
   		else
   		{
   			do
   			{
   				SWORD nResultColumns;
   
   				AFX_ODBC_CALL(::SQLNumResultCols(hstmt, &nResultColumns));
   				if (nResultColumns != 0)
   				{
   					do
   					{
   						AFX_ODBC_CALL(::SQLFetch(hstmt));
   					} while (CheckHstmt(nRetCode, hstmt) &&
   						nRetCode != SQL_NO_DATA_FOUND);
   				}
   				AFX_ODBC_CALL(::SQLMoreResults(hstmt));
   			} while (CheckHstmt(nRetCode, hstmt) &&
   				nRetCode != SQL_NO_DATA_FOUND);
   			// ******** FIX ***********
   			if (!CheckHstmt(nRetCode, hstmt))
   				AfxThrowDBException(nRetCode, this, hstmt);
   			// *******END FIX *********
   		}
   	}
   	CATCH_ALL(e)
   	{
   		::SQLCancel(hstmt);
   		AFX_SQL_SYNC(::SQLFreeStmt(hstmt, SQL_DROP));
   		THROW_LAST();
   	}
   	END_CATCH_ALL
   
   	AFX_SQL_SYNC(::SQLFreeStmt(hstmt, SQL_DROP));
   	
   } 




3. Add the following #include to the MyDatabase.cpp implementation file:

   
   #include "atlconv.h" 

   This code ensures that some of the macros that are used in the implementation will be defined.



4. Change the code in the menu handler that was created previously to use the new class instead of the CDatabase class:




CMyDatabase db;
... 

5. Insert the following #include in the implementation file where your menu handler is defined:




#include "MyDatabase.h" 

6. Recompile and run the code.

Additional query words:

Keywords : kbDatabase kbMDAC kbODBC kbVC600 kbGrpVCDB
Version : winnt:6.0
Platform : winnt
Issue type : kbbug