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Environment: VC++, SQL Server
Have you ever tried to issue multiple direct ODBC calls only to have some of the calls after the first fail? I encountered this problem on a project I was working on. The first SQL command would complete successfully but some of the following SQL commands would fail. The error produced indicated that an “Invalid cursor state” existed. The message provided me with no clues to what the nature of the problem was. The following sample shows code that fails producing the “Invalid Cursor State” message. The UpdateUserName() function contained the commands that produced the error. The sample was issued to an MS SQL Server running version 6.5:
// // Change a given users name in the SQL database // void CSqlConnector::UpdateUserName( const char * pSysAdmnPwd, const char *pLogin, const char *pNewUserName, const char *pOldUserName ) { CString SqlCommand; try { // a DSN has been created earlier named MyDSN // that points to the SQL server AllocateODBCHandles( "MyDSN", "sa", pSysAdmnPwd ); // issue a direct SQL call (call a system // procedure in this case) SqlCommand.Format( "sp_dropuser %s", pOldUserName ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // // NOTE: this command works without using the allocation/ // deallocation process // // switch to the user database SqlCommand.Format( "USE %s", "MyDatabaseName" ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // // THIS STATEMENT FAILED FOR ME // // add the user with the new name SqlCommand.Format( "sp_adduser %s, %s", pLogin, pNewUserName ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // Release the ODBC handles because // the SQL commands have completed FreeODBCHandles(); } catch(...) { // handle error condition } } // // directly execute an ODBC command // SQLRETURN CSqlConnector::ExecuteDirectODBC( SQLHSTMT hStmt, CString command ) { // // issue the SQL command that is to execute // return SQLExecDirect(hStmt, (unsigned char *)command.operator LPCSTR(), SQL_NTS); } // // void CSqlConnector::AllocateODBCHandles( const CString & DSN, const CString & UID, const CString & Pwd ) { try { // Allocate the Environment Handle SQLAllocHandle( SQL_HANDLE_ENV, SQL_NULL_HANDLE, &m_hEnv ); // Notify ODBC that this is an ODBC 3.0 application. SQLSetEnvAttr(m_hEnv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER) SQL_OV_ODBC3, SQL_IS_INTEGER); // Allocate the Connection handle SQLAllocHandle( SQL_HANDLE_DBC, m_hEnv, &m_hDbc ); // set the connection timeout value to 15 seconds SQLSetConnectOption(m_hDbc, SQL_LOGIN_TIMEOUT, 15); // Connect to the database SQLConnect(m_hDbc, (SQLCHAR*) DSN.operator LPCSTR(), SQL_NTS, (SQLCHAR*) UID.operator LPCSTR(), SQL_NTS, (SQLCHAR*) Pwd.operator LPCSTR(), SQL_NTS); // retrieve a statement handle SQLAllocHandle( SQL_HANDLE_STMT, m_hDbc, &m_hStmt ); } catch(...) { // free the database handle if it exists if( NULL != m_hDbc ) { // close the connection handle SQLDisconnect( m_hDbc ); } // free the environment handle if it exists if( NULL != m_hEnv ) { // free the environment handle SQLFreeHandle( SQL_HANDLE_ENV, m_hEnv ); } } } // // // void CSqlConnector::FreeODBCHandles() { // free the statement handle SQLFreeHandle( SQL_HANDLE_STMT, m_hStmt ); // free the environment handle SQLFreeHandle( SQL_HANDLE_ENV, m_hEnv ); // close the connection handle SQLDisconnect( m_hDbc ); // free the connection handle SQLFreeHandle( SQL_HANDLE_DBC, m_hDbc ); // mark the handles as not in use m_hEnv = NULL; m_hDbc = NULL; m_hStmt = NULL; }
I checked the newsgroups for anyone having the same problem. I found several posts where others encountered the same problem. No answers were posted to their questions. After trying a number of angles I finally stumbled on one that worked. The code worked for me when I allocated the ODBC handles before each command and then deallocated them after each call. The following is a snippet code that demonstrates this method:
// // Change a given users name in the SQL database // void CSqlConnector::UpdateUserName(const char * pSysAdmnPwd, const char *pLogin, const char *pNewUserName, const char *pOldUserName ) { CString SqlCommand; try { // a DSN has been created earlier named MyDSN that // points to the SQL server AllocateODBCHandles( "MyDSN", "sa", pSysAdmnPwd ); // add the login SqlCommand.Format( "sp_dropuser %s", pOldUserName ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // Release the ODBC handles because // the SQL command has completed FreeODBCHandles(); AllocateODBCHandles( "MyDSN", "sa", pAdminPwd )) // switch to the user database SqlCommand.Format( "USE %s", "MyDatabaseName" ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // // THE COMMAND SUCCEEDS THIS TIME // // add the user with the new name SqlCommand.Format( "sp_adduser %s, %s", pLogin, pNewUserName ); ExecuteDirectODBC( m_hStmt, SqlCommand ); // Release the ODBC handles because // the SQL commands have completed FreeODBCHandles(); } catch(...) { // handle error condition } }
I’ve noticed that some statements would work successfully without the allocation/deallocation process. It appears that certain statements need to be “flushed” before other commands may be issued. Closing and opening the ODBC handles appears to handle this. I hope this article helps clear up the same problem for others.