Knowledge Base

FIX: Text Data Truncated When Using optimizeBulkAdd

Article ID: 139511

Article Last Modified on 11/21/2006

APPLIES TO

This article was previously published under Q139511

SYMPTOMS

When you try to use the optimizeBulkAdd flag with a CRecordset object, text fields may be truncated. For example, if the first insertion in the table inserts a text value in field1 that is four characters long and a second insertion inserts a text value in field1 that is five characters, the text in the second insertion will be truncated to four characters, the length of the text from the first insertion.

CAUSE

MFC is incorrectly binding the length of the parameters it uses in the INSERT INTO statement it constructs for adding a record.

RESOLUTION

Use either of these two workarounds:

  • As the first record you add, insert a dummy record that contains strings with the maximum length you want for the text fields in the recordset. Every record after this first insertion will always have text values with lengths that are less than or equal to the length of the text fields in the dummy record. When you have finished inserting records, delete the dummy record. -or-

  • Replace the RFX_Text() function calls in your CRecordset's DoFieldExchange() with the following RFX_Text2() function, which performs the correct binding for the parameters used in the INSERT INTO statement used internally by MFC to add a record. In your recordset's header file add: 
       void RFX_Text2(CFieldExchange* pFX, const char* szName,
                  CString& value, int nMaxLength=255,
                  int nColumnType=SQL_VARCHAR);

   In your recordset's .cpp file add:

   void RFX_Text2(CFieldExchange* pFX, const char* szName,
     CString& value, int nMaxLength /*=255*/ , int nColumnType
                                             /* =SQL_VARCHAR */)
   {
     if (pFX->m_nOperation != CFieldExchange::NameValue &&
         pFX->m_nOperation != CFieldExchange::Value &&
         pFX->m_nOperation != CFieldExchange::BindParam)
     {
        RFX_Text(pFX, szName, value, nMaxLength, nColumnType);
        return;
     }

     ASSERT(AfxIsValidAddress(pFX, sizeof(CFieldExchange)));
     ASSERT(AfxIsValidString(szName));
     ASSERT(AfxIsValidAddress&value, sizeof(CString)));

     RETCODE nRetCode;
     UINT nField;
     if (!pFX->IsFieldType(&nField))
        return;

     LONG* plLength = pFX->m_prs->GetFieldLength(pFX);
     switch (pFX->m_nOperation)
     {
       case CFieldExchange::NameValue:
        if (pFX->m_prs->IsFieldFlagDirty(nField,pFX->m_nFieldType))
         {
           *pFX->m_pstr += pFX->m_prs->m_pDatabase->QuoteName(szName);
           *pFX->m_pstr += "=";
         }
           // Fall through

       case CFieldExchange::Value:
         if (pFX->m_prs->IsFieldFlagDirty(nField, pFX->m_nFieldType))
         {

            // If user marked column NULL, reflect this in length
          if (pFX->m_prs->IsFieldFlagNull(nField, pFX->m_nFieldType))
             *plLength = SQL_NULL_DATA;
          else
             *plLength = SQL_NTS;

            // If optimizing for bulk add, just set length.
        if (!(pFX->m_prs->m_dwOptions & CRecordset::optimizeBulkAdd))
            {
              *pFX->m_pstr += "?";
              *pFX->m_pstr += pFX->m_lpszSeparator;
              pFX->m_nParamFields++;

              AFX_SQL_SYNC(::SQLSetParam(pFX->m_hstmt,
                (unsigned short int)pFX->m_nParamFields,
                SQL_C_CHAR,
                (short int)nColumnType,
                nMaxLength,
                0,
                value.GetBuffer(0),
                plLength));
              value.ReleaseBuffer();

              if (nRetCode != SQL_SUCCESS)
                pFX->m_prs->ThrowDBException(nRetCode, pFX->m_hstmt);
             }
           }
           return;

         case CFieldExchange::BindParam:
           *plLength = SQL_NTS;
           // Preallocate to nMaxLength
           value.GetBufferSetLength(nMaxLength);
           AFX_SQL_SYNC(::SQLSetParam(pFX->m_hstmt,
            (unsigned short int)nField,
            (short int)SQL_C_CHAR,
            (short int)nColumnType,
            nMaxLength,
            0,
            value.GetBuffer(0),
            plLength));
            value.ReleaseBuffer();

            if (nRetCode != SQL_SUCCESS)
              pFX->m_prs->ThrowDBException(nRetCode, pFX->m_hstmt);
            return;
     }
   }

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. The code has been corrected in Visual C++ version 2.2 and later.

MORE INFORMATION

Sample Code to Reproduce Problem

CMyRecordSet rs;
rs.Open(CRecordset::snapshot, NULL, CRecordset::optimizeBulkAdd);
rs.AddNew();
rs.m_field1="1234";
rs.Update();
rs.AddNew();
rs.m_field1="12345";
rs.Update();
rs.Close();
The table will look like this: 
   field1
   ------
   1234
   1234
instead of this: 
   field1
   ------
   1234
   12345

REFERENCES

See the following references for more information about the problem and workaround:

Following is the information from the Msetup.hlp file on the Visual C++ compact disc that talks about the optimizeBulkAdd feature:

The MFC CRecordset class has a new optimization (in both 16- and 32-bit versions) that improves efficiency when you're adding new records in bulk to a table. A new option for the dwOptions parameter to the CRecordset::Open member function, optimizeBulkAdd, improves performance when you're adding multiple records consecutively without calling Requery or Close. Only those fields that are "dirty" prior to the first Update call are marked as "dirty" for subsequent AddNew/Update calls. If you are using the database classes to take advantage of the ::SQLSetPos API function for adding, editing, and deleting records, this optimization is unnecessary. If the ODBC Cursor Library is loaded or the ODBC driver doesn't support adding, editing, and deleting via ::SQLSetPos, this optimization should improve bulk add performance. To turn on this optimization, set the dwOptions parameter in the Open call for your recordset to: 

       appendOnly | optimizeBulkAdd

Additional query words: 1.5 1.50 1.52

Keywords: kbbug kbdatabase kbfix KB139511


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