DOCUMENT:Q148805 03-AUG-2001 [visualc] TITLE :FIX: CDaoTableDef CreateField Cannot Set "Allow Zero Length" PRODUCT :Microsoft C Compiler PROD/VER:winnt: OPER/SYS: KEYWORDS:kbProgramming kbDAOsearch kbDatabase kbMFC kbVCkbbuglist kbfixlist ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - The Microsoft Foundation Classes (MFC), included with: - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.0 ------------------------------------------------------------------------------- SYMPTOMS ======== The CDaoFieldInfo structure has a member variable, m_bAllowZeroLength, that allows you to set the "Allow Zero Length" property for a text or memo field in a Microsoft Access table. However, m_bAllowZeroLength cannot be set to TRUE in an MFC DAO application. The application does not complain when you call CDaoTableDef::CreateField () to set this to TRUE, but the table in Microsoft Access shows that the field property does not allow zero length. Later if you try to put a NULL value in the field, a CDAOException is thrown which says "Field cannot be Null." CAUSE ===== AfxSetFieldInfo in Daocore.cpp (which is called by CreateField) has this code: if (!fieldinfo.m_bAllowZeroLength) DAO_CHECK(pDAOField->put_AllowZeroLength(AFX_DAO_FALSE)); Because the default in Microsoft Access is FALSE (does not allow zero length), the above code doesn't set it to TRUE. RESOLUTION ========== 1. Copy the code for AfxSetFieldInfo() from Daocore.cpp into your project as a separate function. Then modify the line containing the bug. Remove the exclamation mark (!) in the first line, and change AFX_DAO_FALSE to AFX_DAO_TRUE in the second line: void MyCreateField() { CDaoDatabase db; db.Open("c:\\msdev\\projects\\daoenrol\\stdreg32.mdb", FALSE, FALSE); // create a tabledef CDaoTableDef td ( &db ); td.Create(_T("Table1"),0,_T("Table1"), NULL); // create a FieldInfo structure struct CDaoFieldInfo m_FI; m_FI.m_nOrdinalPosition = 0; // always initialize the rest m_FI.m_strName = _T("MyField"); m_FI.m_nType = dbText ; m_FI.m_lSize = 20; m_FI.m_bAllowZeroLength = TRUE; // To set "Allow Zero Length" m_FI.m_strDefaultValue = _T(""); m_FI.m_bRequired = FALSE; m_FI.m_lAttributes = dbUpdatableField; m_FI.m_strValidationRule = _T(""); m_FI.m_strValidationText = _T(""); // Copy code from CDaoTableDef::CreateField() DAOField* pDAOField; // Create the DAO field object (setting basic properties) // DAO_CHECK(m_pDAOTableDef->CreateField( DAO_CHECK(td.m_pDAOTableDef->CreateField( COleVariant(m_FI.m_strName, VT_BSTRT), COleVariant(m_FI.m_nType), COleVariant(m_FI.m_lSize), &pDAOField)); TRY { // Basic properties already set, so set the rest MyAfxSetFieldInfo(pDAOField, m_FI); // Append the field object to the fields collection if (td.m_pDAOFields == NULL) // cannot call private member function //td.InitFieldsCollection(); DAO_CHECK(td.m_pDAOTableDef->get_Fields (&(td.m_pDAOFields))); DAO_CHECK(td.m_pDAOFields->Append(pDAOField)); } CATCH_ALL(e) { pDAOField->Release(); THROW_LAST(); } END_CATCH_ALL pDAOField->Release(); td.Append(); } STATUS ====== Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual C++, 32-bit Edition, version 4.1. Additional query words: ====================================================================== Keywords : kbProgramming kbDAOsearch kbDatabase kbMFC kbVC kbbuglist kbfixlist Technology : kbAudDeveloper kbMFC Version : winnt: Issue type : kbbug Solution Type : kbfix ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.