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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
class CMyDatabase : public 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
static const TCHAR szODBC[] = _T("ODBC;");
// 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 CMyDatabase::Open(LPCTSTR lpszDSN, BOOL bExclusive,
BOOL bReadonly, LPCTSTR lpszConnect, BOOL bUseCursorLib)
{
UCHAR szConnectOutput[MAX_CONNECT_LEN];
#ifdef _68K_
if(nClassObject == 0)
AfxThrowDBException(AFX_SQL_ERROR_ODBC_LOAD_FAILED, NULL,
SQL_NULL_HSTMT);
#endif
ASSERT_VALID(this); ASSERT(lpszDSN == NULL || AfxIsValidString(lpszDSN)); ASSERT(lpszConnect == NULL || AfxIsValidString(lpszConnect));
// Exclusive access not supported.
ASSERT(!bExclusive); UNUSED(bExclusive); // unused in release builds
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
if (_tcsnicmp(m_strConnect, szODBC, lstrlen(szODBC)) != 0) {
TRACE0("Error: Missing 'ODBC' prefix on connect string.\n");
return FALSE;
}
// Strip "ODBC;"
m_strConnect = m_strConnect.Right(m_strConnect.GetLength()
- lstrlen(szODBC));
if (lpszDSN != NULL && lstrlen(lpszDSN) != 0)
{
// 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;
#ifndef _MAC
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));
#else
AFX_SQL_SYNC(::SQLDriverConnect(m_hdbc, GetWrapperWindow(pWnd->m_hWnd),
(UCHAR*)(const char*)m_strConnect, SQL_NTS,
szConnectOutput, _countof(szConnectOutput),
&nResult, SQL_DRIVER_COMPLETE));
#endif
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))
{
#ifdef _DEBUG
if (pWnd->m_hWnd == NULL)
TRACE0("Error: No default window (AfxGetApp()->m_pMainWnd) for
SQLDriverConnect.\n");
#endif
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;
#ifdef _DEBUG
if (!m_bUpdatable && (afxTraceFlags & traceDatabase))
TRACE0("Warning: data source is readonly.\n");
#endif
}
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 = ' ';
#ifdef _DEBUG
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);
}
}
}
#endif
}
CATCH_ALL(e)
{
Free();
THROW_LAST();
}
END_CATCH_ALL
return TRUE;
}
REFERENCES
Class Library Reference for CDatabase::OpenEx member function.
Copyright (c) 1999 - 2001, robert han, all rigths are reserved.