Miscellany - This time I will cover some miscellaneous stuff about the database programming.

Error Information

When your connections or queries fail, it obviously would be nice to know why. There are several methods for getting some error info from query and transaction object.

• WQuery::GetErrorInfo - this is my personal favorite. I use it like so:

  WString msg;
  if (!query_1->Open()) {
      query_1->GetErrorInfo( &msg );
      msg = "Error "+msg+" occurred on query +"query_1->GetSQL();
  }

• Another more detailed method to get error information is to use the WTransaction::GetErrorList method:

  // Code example lifted from the Power++ Programmer's Guide
  WDataErrorArray errList=transaction_1->GetErrorList();
  for (WInt i = 0; i < errList.GetCount(); i++ ) {
      WLong errCode = errList[i].GetErrorCode();
      WString errMsg = errList[i].GetErrorMessage();
      WLong funcCode = errList[i].GetFunctionCode();
      WLong natCode = errList[i].GetNativeCode();
      WString state = errList[i].GetSQLState();
      // then do something with these values
  }

DBMS Independence

As I touched on in previous chapters in this series, you may come across the need to make your applications portable across various database systems. There are a couple of points to keep in mind:

• Use ODBC. In an earlier article I detailed how to change the datasource at run time in order to change databases (that have the same structure). If you write originally to ODBC you can always go back and write a DBMS specific version if you need.

• Use standard SQL. Obviously if you use SQL that is specific to a DBMS then your application will not port. However, I have never found a situation where I had to use DBMS-specific SQL. This point applies even more if you use stored procedures or triggers. Those seem to be less standardised among various databases so make sure the behaviour is as expected.

If you keep these two points in mind, your applications should port for any DBMS (I have personally tested this from Paradox to MS SQL DBMS's).

If you have any questions or suggestions for topics, feel free to e-mail them directly to me at dosten(at)earthlink.net.

Until next time...