DOCUMENT:Q138767 30-JUL-2001 [visualc] TITLE :FIX: CreateRelation Method Fails with Non-UNICODE Build PRODUCT :Microsoft C Compiler PROD/VER:winnt: OPER/SYS: KEYWORDS:kbcode kbDAOsearch kbDatabase kbMFC kbVC kbVC410fix ====================================================================== ------------------------------------------------------------------------------- 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 CDaoDatabase::CreateRelation() method may fail if an application is built as a non-UNICODE application. It is possible that a messagebox will appear that states: Invalid field name '' in definition of index or relationship CAUSE ===== A bug exists in the CDaoDatabase::CreateRelation() function. In \Msdev\Mfc\Src\Daocore.cpp, you can see the following code in the CreateRelation() function: COleVariant var; var = relinfo.m_pFieldInfos[nIndex].m_strForeignName; DAO_CHECK(pDAOField->put_ForeignName(V_BSTR(&var))); This code is incorrect. Here is the correct code: COleVariant var(relinfo.m_pFieldInfos[nIndex].m_strForeignName, VT_BSTRT); DAO_CHECK(pDAOField->put_ForeignName(V_BSTR(&var))); The fixed code ensures that the BSTR for the variant will be in ANSI format for non-UNICODE versions of an application and will be in UNICODE format for UNICODE versions of an application. RESOLUTION ========== Perform the following steps: 1. Derive a new class from CDaoDatabase. 2. Add the function prototypes for the two CreateRelation() functions to your new class declaration. 3. Copy the two CreateRelation() functions from Daocore.cpp to the CreateRelation() functions of your new CDaoDatabase-derived class. 4. Change the following code in your new CreateRelation(CDaoRelationInfo& relinfo) method from: COleVariant var; var = relinfo.m_pFieldInfos[nIndex].m_strForeignName; DAO_CHECK(pDAOField->put_ForeignName(V_BSTR(&var))); to: COleVariant var(relinfo.m_pFieldInfos[nIndex].m_strForeignName, VT_BSTRT); DAO_CHECK(pDAOField->put_ForeignName(V_BSTR(&var))); 5. Declare a local VARIANT and initialize it in the overridden function as follows: VARIANT var; var.vt = VT_ERROR; var.scode = DISP_E_PARAMNOTFOUND; This is necessary because the _afxOptionalVariant used in the original CreateRelation() function is defined in DAOCORE.CPP, 6. Replace instances of the _afxOptionalVariant variable with var. Instead of using the CDaoDatabase class, you will use your new CDaoDatabase- derived class. The sample code in this article demonstrates what the new code might look like. STATUS ====== Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ 4.1. MORE INFORMATION ================ Sample Code to Demonstrate Fixed Code ------------------------------------- This demonstrates how you will use your new CDaoDatabase-derived class; in this case called CMyDatabase. CMyDatabase db; db.Open("f:\\test\\relation\\relate.mdb"); db.CreateRelation(_T("mytest"), _T("Table1"), _T("Table2"), dbRelationUnique|dbRelationUpdateCascade,_T("field1"), _T("field1")); db.Close(); Here is the declaration of the new class: class CMyDatabase:public CDaoDatabase { public: void CreateRelation(LPCTSTR lpszName, LPCTSTR lpszTable, LPCTSTR lpszForeignTable, long lAttributes, LPCTSTR lpszField, LPCTSTR lpszForeignField); void CreateRelation(CDaoRelationInfo& relinfo); }; Here is the implementation of the new class: void CMyDatabase::CreateRelation(LPCTSTR lpszName, LPCTSTR lpszTable, LPCTSTR lpszForeignTable, long lAttributes, LPCTSTR lpszField, LPCTSTR lpszForeignField) { ASSERT_VALID(this); CDaoRelationInfo relinfo; CDaoRelationFieldInfo fieldinfo; relinfo.m_strName = lpszName; relinfo.m_strTable = lpszTable; relinfo.m_strForeignTable = lpszForeignTable; relinfo.m_lAttributes = lAttributes; relinfo.m_nFields = 1; relinfo.m_pFieldInfos = &fieldinfo; relinfo.m_pFieldInfos->m_strName = lpszField; relinfo.m_pFieldInfos->m_strForeignName = lpszForeignField; CreateRelation(relinfo); } void CMyDatabase::CreateRelation(CDaoRelationInfo& relinfo) { ASSERT_VALID(this); ASSERT(IsOpen()); ASSERT(relinfo.m_nFields > 0); VARIANT var; var.vt = VT_ERROR; var.scode = DISP_E_PARAMNOTFOUND; // Initialize relations collection so that relation can be // appended later if (m_pDAORelations == NULL) InitRelationsCollection(); DAORelation* pDAORelation = NULL; DAOFields* pDAOFields = NULL; DAOField* pDAOField = NULL; // Create the relation DAO_CHECK(m_pDAODatabase->CreateRelation( COleVariant(relinfo.m_strName, VT_BSTRT), COleVariant(relinfo.m_strTable, VT_BSTRT), COleVariant(relinfo.m_strForeignTable, VT_BSTRT), COleVariant(relinfo.m_lAttributes), &pDAORelation)); TRY { // Get the fields collection for later append of created field DAO_CHECK(pDAORelation->get_Fields(&pDAOFields)); // Create field(s) and set the name and foreign name for (int nIndex = 0; nIndex < relinfo.m_nFields; nIndex++) { // note that we are using 'var' in the following function // instead of _afxOptionalVar declared in DAOCORE.CPP DAO_CHECK(pDAORelation->CreateField( COleVariant(relinfo.m_pFieldInfos[nIndex].m_strName, VT_BSTRT), var, var, &pDAOField)); COleVariant var(relinfo.m_pFieldInfos[nIndex].m_strForeignName, VT_BSTRT); DAO_CHECK(pDAOField->put_ForeignName(V_BSTR(&var))); // Append the field to relation fields collection and // release DAO_CHECK(pDAOFields->Append(pDAOField)); pDAOField->Release(); } DAO_CHECK(m_pDAORelations->Append(pDAORelation)); } CATCH_ALL(e) { // Clean up before throw if (pDAOField != NULL) pDAOField->Release(); if (pDAOFields != NULL) pDAOFields->Release(); pDAORelation->Release(); THROW_LAST(); } END_CATCH_ALL // Clean up if (pDAOField != NULL) pDAOField->Release(); pDAOFields->Release(); pDAORelation->Release(); } Additional query words: kbVC400bug ====================================================================== Keywords : kbcode kbDAOsearch kbDatabase kbMFC kbVC kbVC410fix 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. 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