How To Avoid the ODBC Login Dialog when Using MFC

WINDOWS        | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, versions 1.5, 1.51, 1.52
      - Microsoft Visual C++ 32-bit Edition, versions 2.0, 2.1, 2.2, 4.0,
        4.1, 4.2
  

SUMMARY

By default, when you use the MFC ODBC database classes to connect to a datasource, ODBC invokes a login dialog box that allows the user to type in any necessary information, such as a password, to log in.

With Visual C++ 4.2, use the CDatabase::OpenEx() method to connect to an ODBC datasource with MFC. Inside CDatabase::Connect(), which is called by CDatabase::OpenEx(), is a call to the ODBC API function, SQLDriverConnect, that does the work to connect.

With versions of Visual C++ earlier than 4.2, use the CDatabase::Open() method to connect to an ODBC datasource with MFC. Inside CDatabase::Open() is a call to the ODBC API function, SQLDriverConnect, that does the work to connect.

The last parameter to SQLDriverConnect is a flag indicating whether the ODBC Driver Manager or driver should prompt for more connection information. MFC uses the SQL_DRIVER_COMPLETE flag that instructs ODBC to invoke a login dialog if you do not supply a connect string with all of the information necessary to make a connection.

Occasionally it is preferable to suppress ODBC from creating a dialog by calling SQLDriverConnect and passing SQL_DRIVER_NOPROMPT as the last parameter. The SQL_DRIVER_NOPROMPT flag instructs ODBC to connect with the information passed in the connect string. If the connection string does not contain enough information to connect to the data source, the call to SQLDriverConnect() returns a value of SQL_ERROR.

With Visual C++ 4.2, specify the CDatabase::noOdbcDialog option as the second argument to CDatabase::OpenEx(). This will cause CDatabase::OpenEx() to call SQLDriverConnect with the SQL_DRIVER_NOPROMPT flag.

To accomplish this behavior using the MFC database classes included with versions of Visual C++ before 4.2, you need to derive a new class from CDatabase and override CDatabase::Open().

Copy the code for CDatabase::Open() from the MFC source file Dbcore.cpp. Then change the call to SQLDriverConnect by replacing SQL_DRIVER_COMPLETE with SQL_DRIVER_NOPROMPT.

The second parameter in SQLDriverConnect is a window handle. You need to pass NULL for this.

Also, add a check for a return value of SQL_ERROR.

MORE INFORMATION

Sample code for Visual C++ 4.2 can be found in the online documentation for CDatabase::OpenEx().

Sample Code

// The code provided here works with MFC 4.1.
// Code to work with other versions of MFC before 4.2 will be very similar.
// You just need to copy the source for CDatabase::Open() from
// Dbcore.cpp, make the changes described in this article, and then
// determine which file specific definitions and header files to add
// to your .cpp file.

// MyDataBase.h
// Derive a class from CDatabase

  public:

  Open(LPCTSTR lpszDSN, BOOL bExclusive = FALSE,
       BOOL bReadonly = FALSE, LPCTSTR lpszConnect = "ODBC;",
       BOOL bUseCursorLib = TRUE);

//MyDataBase.cpp
#include "stdafx.h"
#include <afxpriv.h>
#include <afxdisp.h>

#include "MyDataBase.h"

// This line of code is borrowed from Dbcore.cpp

// These two lines are borrowed from Afximpl.h
// determine number of elements in an array (not bytes)
#define _countof(array) (sizeof(array)/sizeof(array[0]))

  BOOL bReadonly, LPCTSTR lpszConnect, BOOL bUseCursorLib)

  UCHAR szConnectOutput[MAX_CONNECT_LEN];

  if(nClassObject == 0)
  AfxThrowDBException(AFX_SQL_ERROR_ODBC_LOAD_FAILED, NULL,
                      SQL_NULL_HSTMT);

ASSERT_VALID(this); ASSERT(lpszDSN == NULL || AfxIsValidString(lpszDSN)); ASSERT(lpszConnect == NULL || AfxIsValidString(lpszConnect));

// Exclusive access not supported.

m_bUpdatable = !bReadonly;

TRY { if (lpszConnect != NULL)

  m_strConnect = lpszConnect;

// For Visual Basic & Microsoft Access compatibility, use the
// "ODBC;" (or "odbc;") prefix to the connect string

  TRACE0("Error: Missing 'ODBC' prefix on connect string.\n");
  return FALSE;

// Strip "ODBC;"

                 - lstrlen(szODBC));

  {
    // Append "DSN=" lpszDSN
    m_strConnect += ";DSN=";
     m_strConnect += lpszDSN;
   }

     AllocConnect();

     RETCODE nRetCode;
     // Turn on cursor lib support
     if (bUseCursorLib)
     {
       AFX_SQL_SYNC(::SQLSetConnectOption(m_hdbc,
           SQL_ODBC_CURSORS, SQL_CUR_USE_ODBC));
         // With cursor library added records immediately in result set
         m_bIncRecordCountOnAdd = TRUE;
       }

       HWND hWndTop;
       CWnd* pWnd = CWnd::GetSafeOwner(NULL, &hWndTop);
       if (pWnd == NULL)
         pWnd = CWnd::GetDesktopWindow();
       ASSERT_VALID(pWnd);

       SWORD nResult;

       USES_CONVERSION;

   // Code before it was changed:
   //    AFX_SQL_SYNC(::SQLDriverConnect(m_hdbc, pWnd->m_hWnd,
   //      (UCHAR*)T2A((LPCTSTR)m_strConnect), SQL_NTS,
   //      szConnectOutput, _countof(szConnectOutput),
   //      &nResult, SQL_DRIVER_COMPLETE));

       AFX_SQL_SYNC(::SQLDriverConnect(m_hdbc, NULL,
         (UCHAR*)(const char*)m_strConnect, SQL_NTS,
         szConnectOutput, _countof(szConnectOutput),
         &nResult, SQL_DRIVER_NOPROMPT));

    AFX_SQL_SYNC(::SQLDriverConnect(m_hdbc, GetWrapperWindow(pWnd->m_hWnd),
         (UCHAR*)(const char*)m_strConnect, SQL_NTS,
         szConnectOutput, _countof(szConnectOutput),
         &nResult, SQL_DRIVER_COMPLETE));

    if (hWndTop != NULL)
      ::EnableWindow(hWndTop, TRUE);

    // Code before it was changed:
     //    if (nRetCode == SQL_NO_DATA_FOUND)
    // Now need to check for SQL_ERROR too
    if ((nRetCode == SQL_NO_DATA_FOUND) || (nRetCode == SQL_ERROR))
    {
      Free();
      return FALSE;
    }

    if (!Check(nRetCode))
    {

    if (pWnd->m_hWnd == NULL)
       TRACE0("Error: No default window (AfxGetApp()->m_pMainWnd) for
   SQLDriverConnect.\n");

      ThrowDBException(nRetCode);
    }

    // Connect strings must have "ODBC;"
    m_strConnect = szODBC;
    // Save connect string returned from ODBC
 m_strConnect += (char*)szConnectOutput;

    SWORD nAPIConformance;
    AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_ODBC_API_CONFORMANCE,
      &nAPIConformance, sizeof(nAPIConformance), &nResult));
    if (!Check(nRetCode))
      ThrowDBException(nRetCode);

    if (nAPIConformance < SQL_OAC_LEVEL1)
      ThrowDBException(AFX_SQL_ERROR_API_CONFORMANCE);

    SWORD nSQLConformance;
    AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_ODBC_SQL_CONFORMANCE,
      &nSQLConformance, sizeof(nSQLConformance), &nResult));
    if (!Check(nRetCode))
      ThrowDBException(nRetCode);

    if (nSQLConformance < SQL_OSC_MINIMUM)
      ThrowDBException(AFX_SQL_ERROR_SQL_CONFORMANCE);

    AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_CURSOR_COMMIT_BEHAVIOR,
      &m_nCursorCommitBehavior, sizeof(m_nCursorCommitBehavior),
      &nResult));
    if (!Check(nRetCode))
      m_nCursorCommitBehavior = SQL_ERROR;

    AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_CURSOR_ROLLBACK_BEHAVIOR,
      &m_nCursorRollbackBehavior, sizeof(m_nCursorRollbackBehavior),
      &nResult));
   if (!Check(nRetCode))
     m_nCursorRollbackBehavior = SQL_ERROR;

   UDWORD dwGetDataExtensions;
   AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_GETDATA_EXTENSIONS,
     &dwGetDataExtensions, sizeof(dwGetDataExtensions),
     &nResult));
   if (!Check(nRetCode))
     dwGetDataExtensions = 0;
   if (dwGetDataExtensions & SQL_GD_BOUND)
     m_dwUpdateOptions = AFX_SQL_GDBOUND;
   else
     m_dwUpdateOptions = 0;

   // Set required transaction support for CRecordset cursors
   if ((m_nCursorCommitBehavior == SQL_CB_PRESERVE) &&
     (m_nCursorRollbackBehavior == SQL_CB_PRESERVE))
     m_bTransactions = TRUE;

   if (m_bUpdatable)
   {
     // Make sure data source is Updatable
     char szReadOnly[10];
     AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_DATA_SOURCE_READ_ONLY,
       szReadOnly, _countof(szReadOnly), &nResult));
     if (Check(nRetCode) && nResult == 1)
       m_bUpdatable = !(lstrcmpA(szReadOnly, "Y") == 0);
     else
       m_bUpdatable = FALSE;

      if (!m_bUpdatable && (afxTraceFlags & traceDatabase))
        TRACE0("Warning: data source is readonly.\n");

    }
    else
    {
      // Make data source is Updatable
      AFX_SQL_SYNC(::SQLSetConnectOption(m_hdbc,
        SQL_ACCESS_MODE, SQL_MODE_READ_ONLY));
    }

    char szIDQuoteChar[2];
    AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_IDENTIFIER_QUOTE_CHAR,
      szIDQuoteChar, _countof(szIDQuoteChar), &nResult));
    if (Check(nRetCode) && nResult == 1)
      m_chIDQuoteChar = szIDQuoteChar[0];
    else
      m_chIDQuoteChar = ' ';

    if (afxTraceFlags & traceDatabase)
    {
      char szInfo[64];
      AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_DBMS_NAME,
        szInfo, _countof(szInfo), &nResult));
      if (Check(nRetCode))
      {
        CString strInfo = szInfo;
        TRACE1("DBMS: %s\n", strInfo);
        AFX_SQL_SYNC(::SQLGetInfo(m_hdbc, SQL_DBMS_VER,
          szInfo, _countof(szInfo), &nResult));
        if (Check(nRetCode))
        {
          strInfo = szInfo;
          TRACE1(", Version: %s\n", strInfo);
        }
      }
    }

  }
  CATCH_ALL(e)
  {
    Free();
    THROW_LAST();
  }
  END_CATCH_ALL

  return TRUE;

REFERENCES

Class Library Reference for CDatabase::OpenEx member function.