RWDBInserter.isValid() always returns OK even the SQL generated is incorrect

I have an RWDBInserter object and executed. I know there is a semantic error. But when I check my inserter object status with the isValid() function, it shows ok. Why?

RWDBInserter is one of big objects which can be re-used. For instance, it can be executed many times. That's why a particular execution should not been bounded with its object.

DBTools uses RWDBResult to reflect each execution. So the RWDBResult object
should be checked to see if this time the  execution has succeeded or not.
Here is an example:

  RWDBInserter ins= myTable.inserter();
  ins << 10;
  RWDBResult res= ins.execute(myConnection);
  if( res.isValid() )
  {
   //...
  }
  else
  {
   //...
  }

Or the user can use error call back function to catch errors. 
Similar classes are RWDBSelector, RWDBUpdater, RWDBStoredProc, etc.